From 51c3ff8d75d9c784297ad587a31a37acd89499d8 Mon Sep 17 00:00:00 2001
From: Oran Agra <oran@redislabs.com>
Date: Tue, 29 Oct 2019 17:59:09 +0200
Subject: [PATCH 01/15] Modules hooks: complete missing hooks for the initial
 set of hooks

* replication hooks: role change, master link status, replica online/offline
* persistence hooks: saving, loading, loading progress
* misc hooks: cron loop, shutdown, module loaded/unloaded
* change the way hooks test work, and add tests for all of the above

startLoading() now gets flag indicating what is loaded.
stopLoading() now gets an indication of success or failure.
adding startSaving() and stopSaving() with similar args and role.
---
 src/aof.c                      |  14 +-
 src/debug.c                    |   2 +-
 src/module.c                   | 161 +++++++++++++++++----
 src/networking.c               |   5 +
 src/rdb.c                      |  80 ++++++++---
 src/rdb.h                      |  11 +-
 src/redis-check-rdb.c          |   6 +-
 src/redismodule.h              |  86 +++++++++--
 src/replication.c              |  55 ++++++-
 src/server.c                   |  11 +-
 src/server.h                   |  10 +-
 tests/modules/hooks.c          | 256 +++++++++++++++++++++++++++++++--
 tests/unit/moduleapi/hooks.tcl | 134 +++++++++++++++--
 13 files changed, 737 insertions(+), 94 deletions(-)

diff --git a/src/aof.c b/src/aof.c
index 0e3648ff0..dda9579e3 100644
--- a/src/aof.c
+++ b/src/aof.c
@@ -731,7 +731,7 @@ int loadAppendOnlyFile(char *filename) {
     server.aof_state = AOF_OFF;
 
     fakeClient = createAOFClient();
-    startLoadingFile(fp, filename);
+    startLoadingFile(fp, filename, RDBFLAGS_AOF_PREAMBLE);
 
     /* Check if this AOF file has an RDB preamble. In that case we need to
      * load the RDB file and later continue loading the AOF tail. */
@@ -746,7 +746,7 @@ int loadAppendOnlyFile(char *filename) {
         serverLog(LL_NOTICE,"Reading RDB preamble from AOF file...");
         if (fseek(fp,0,SEEK_SET) == -1) goto readerr;
         rioInitWithFile(&rdb,fp);
-        if (rdbLoadRio(&rdb,NULL,1) != C_OK) {
+        if (rdbLoadRio(&rdb,RDBFLAGS_AOF_PREAMBLE,NULL) != C_OK) {
             serverLog(LL_WARNING,"Error reading the RDB preamble of the AOF file, AOF loading aborted");
             goto readerr;
         } else {
@@ -767,6 +767,7 @@ int loadAppendOnlyFile(char *filename) {
         if (!(loops++ % 1000)) {
             loadingProgress(ftello(fp));
             processEventsWhileBlocked();
+            processModuleLoadingProgressEvent(1);
         }
 
         if (fgets(buf,sizeof(buf),fp) == NULL) {
@@ -859,7 +860,7 @@ loaded_ok: /* DB loaded, cleanup and return C_OK to the caller. */
     fclose(fp);
     freeFakeClient(fakeClient);
     server.aof_state = old_aof_state;
-    stopLoading();
+    stopLoading(1);
     aofUpdateCurrentSize();
     server.aof_rewrite_base_size = server.aof_current_size;
     server.aof_fsync_offset = server.aof_current_size;
@@ -1400,9 +1401,11 @@ int rewriteAppendOnlyFile(char *filename) {
     if (server.aof_rewrite_incremental_fsync)
         rioSetAutoSync(&aof,REDIS_AUTOSYNC_BYTES);
 
+    startSaving(RDBFLAGS_AOF_PREAMBLE);
+
     if (server.aof_use_rdb_preamble) {
         int error;
-        if (rdbSaveRio(&aof,&error,RDB_SAVE_AOF_PREAMBLE,NULL) == C_ERR) {
+        if (rdbSaveRio(&aof,&error,RDBFLAGS_AOF_PREAMBLE,NULL) == C_ERR) {
             errno = error;
             goto werr;
         }
@@ -1465,15 +1468,18 @@ int rewriteAppendOnlyFile(char *filename) {
     if (rename(tmpfile,filename) == -1) {
         serverLog(LL_WARNING,"Error moving temp append only file on the final destination: %s", strerror(errno));
         unlink(tmpfile);
+        stopSaving(0);
         return C_ERR;
     }
     serverLog(LL_NOTICE,"SYNC append only file rewrite performed");
+    stopSaving(1);
     return C_OK;
 
 werr:
     serverLog(LL_WARNING,"Write error writing append only file on disk: %s", strerror(errno));
     fclose(fp);
     unlink(tmpfile);
+    stopSaving(0);
     return C_ERR;
 }
 
diff --git a/src/debug.c b/src/debug.c
index 179f6d2c9..a2d37337d 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -417,7 +417,7 @@ NULL
         }
         emptyDb(-1,EMPTYDB_NO_FLAGS,NULL);
         protectClient(c);
-        int ret = rdbLoad(server.rdb_filename,NULL);
+        int ret = rdbLoad(server.rdb_filename,NULL,RDBFLAGS_NONE);
         unprotectClient(c);
         if (ret != C_OK) {
             addReplyError(c,"Error trying to load the RDB dump");
diff --git a/src/module.c b/src/module.c
index 2a1bda879..57e388881 100644
--- a/src/module.c
+++ b/src/module.c
@@ -1620,6 +1620,27 @@ int modulePopulateClientInfoStructure(void *ci, client *client, int structver) {
     return REDISMODULE_OK;
 }
 
+/* This is an helper for moduleFireServerEvent() and other functions:
+ * It populates the replication info structure with the appropriate
+ * fields depending on the version provided. If the version is not valid
+ * then REDISMODULE_ERR is returned. Otherwise the function returns
+ * REDISMODULE_OK and the structure pointed by 'ri' gets populated. */
+int modulePopulateReplicationInfoStructure(void *ri, int structver) {
+    if (structver != 1) return REDISMODULE_ERR;
+
+    RedisModuleReplicationInfoV1 *ri1 = ri;
+    memset(ri1,0,sizeof(*ri1));
+    ri1->version = structver;
+    ri1->master = server.masterhost==NULL;
+    ri1->masterhost = server.masterhost? server.masterhost: "";
+    ri1->masterport = server.masterport;
+    ri1->replid1 = server.replid;
+    ri1->replid2 = server.replid2;
+    ri1->repl1_offset = server.master_repl_offset;
+    ri1->repl2_offset = server.second_replid_offset;
+    return REDISMODULE_OK;
+}
+
 /* Return information about the client with the specified ID (that was
  * previously obtained via the RedisModule_GetClientId() API). If the
  * client exists, REDISMODULE_OK is returned, otherwise REDISMODULE_ERR
@@ -5780,8 +5801,8 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *
  *          The following sub events are available:
  *
- *              REDISMODULE_EVENT_REPLROLECHANGED_NOW_MASTER
- *              REDISMODULE_EVENT_REPLROLECHANGED_NOW_REPLICA
+ *              REDISMODULE_SUBEVENT_REPLROLECHANGED_NOW_MASTER
+ *              REDISMODULE_SUBEVENT_REPLROLECHANGED_NOW_REPLICA
  *
  *          The 'data' field can be casted by the callback to a
  *          RedisModuleReplicationInfo structure with the following fields:
@@ -5791,24 +5812,30 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *              int masterport; // master instance port for NOW_REPLICA
  *              char *replid1; // Main replication ID
  *              char *replid2; // Secondary replication ID
+ *              uint64_t repl1_offset; // Main replication offset
  *              uint64_t repl2_offset; // Offset of replid2 validity
- *              uint64_t main_repl_offset; // Replication offset
  *
  *      RedisModuleEvent_Persistence
  *
  *          This event is called when RDB saving or AOF rewriting starts
  *          and ends. The following sub events are available:
  *
- *              REDISMODULE_EVENT_LOADING_RDB_START        // BGSAVE start
- *              REDISMODULE_EVENT_LOADING_RDB_END          // BGSAVE end
- *              REDISMODULE_EVENT_LOADING_SYNC_RDB_START   // SAVE start
- *              REDISMODULE_EVENT_LOADING_SYNC_RDB_START   // SAVE end
- *              REDISMODULE_EVENT_LOADING_AOF_START        // AOF rewrite start
- *              REDISMODULE_EVENT_LOADING_AOF_END          // AOF rewrite end
+ *              REDISMODULE_SUBEVENT_PERSISTENCE_RDB_START
+ *              REDISMODULE_SUBEVENT_PERSISTENCE_AOF_START
+ *              REDISMODULE_SUBEVENT_PERSISTENCE_SYNC_RDB_START
+ *              REDISMODULE_SUBEVENT_PERSISTENCE_ENDED
+ *              REDISMODULE_SUBEVENT_PERSISTENCE_FAILED
  *
  *          The above events are triggered not just when the user calls the
  *          relevant commands like BGSAVE, but also when a saving operation
  *          or AOF rewriting occurs because of internal server triggers.
+ *          The SYNC_RDB_START sub events are happening in the forground due to
+ *          SAVE command, FLUSHALL, or server shutdown, and the other RDB and
+ *          AOF sub events are executed in a background fork child, so any
+ *          action the module takes can only affect the generated AOF or RDB,
+ *          but will not be reflected in the parent process and affect connected
+ *          clients and commands. Also note that the AOF_START sub event may end
+ *          up saving RDB content in case of an AOF with rdb-preamble.
  *
  *      RedisModuleEvent_FlushDB
  *
@@ -5816,8 +5843,8 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *          because of replication, after the replica synchronization)
  *          happened. The following sub events are available:
  *
- *              REDISMODULE_EVENT_FLUSHDB_START
- *              REDISMODULE_EVENT_FLUSHDB_END
+ *              REDISMODULE_SUBEVENT_FLUSHDB_START
+ *              REDISMODULE_SUBEVENT_FLUSHDB_END
  *
  *          The data pointer can be casted to a RedisModuleFlushInfo
  *          structure with the following fields:
@@ -5841,12 +5868,15 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *          replica is loading the RDB file from the master.
  *          The following sub events are available:
  *
- *              REDISMODULE_EVENT_LOADING_RDB_START
- *              REDISMODULE_EVENT_LOADING_RDB_END
- *              REDISMODULE_EVENT_LOADING_MASTER_RDB_START
- *              REDISMODULE_EVENT_LOADING_MASTER_RDB_END
- *              REDISMODULE_EVENT_LOADING_AOF_START
- *              REDISMODULE_EVENT_LOADING_AOF_END
+ *              REDISMODULE_SUBEVENT_LOADING_RDB_START
+ *              REDISMODULE_SUBEVENT_LOADING_AOF_START
+ *              REDISMODULE_SUBEVENT_LOADING_REPL_START
+ *              REDISMODULE_SUBEVENT_LOADING_ENDED
+ *              REDISMODULE_SUBEVENT_LOADING_FAILED
+ *
+ *          Note that AOF loading may start with an RDB data in case of
+ *          rdb-preamble, in which case you'll only recieve an AOF_START event.
+ *
  *
  *      RedisModuleEvent_ClientChange
  *
@@ -5855,8 +5885,8 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *          structure, documented in RedisModule_GetClientInfoById().
  *          The following sub events are available:
  *
- *              REDISMODULE_EVENT_CLIENT_CHANGE_CONNECTED
- *              REDISMODULE_EVENT_CLIENT_CHANGE_DISCONNECTED
+ *              REDISMODULE_SUBEVENT_CLIENT_CHANGE_CONNECTED
+ *              REDISMODULE_SUBEVENT_CLIENT_CHANGE_DISCONNECTED
  *
  *      RedisModuleEvent_Shutdown
  *
@@ -5869,8 +5899,8 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *          replica since it gets disconnected.
  *          The following sub events are availble:
  *
- *              REDISMODULE_EVENT_REPLICA_CHANGE_ONLINE
- *              REDISMODULE_EVENT_REPLICA_CHANGE_OFFLINE
+ *              REDISMODULE_SUBEVENT_REPLICA_CHANGE_ONLINE
+ *              REDISMODULE_SUBEVENT_REPLICA_CHANGE_OFFLINE
  *
  *          No additional information is available so far: future versions
  *          of Redis will have an API in order to enumerate the replicas
@@ -5885,6 +5915,11 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *          this changes depending on the "hz" configuration.
  *          No sub events are available.
  *
+ *          The data pointer can be casted to a RedisModuleCronLoop
+ *          structure with the following fields:
+ *
+ *              int32_t hz;  // Approximate number of events per second.
+ *
  *  RedisModuleEvent_MasterLinkChange
  *
  *          This is called for replicas in order to notify when the
@@ -5894,8 +5929,38 @@ void ModuleForkDoneHandler(int exitcode, int bysignal) {
  *          replication is happening correctly.
  *          The following sub events are available:
  *
- *              REDISMODULE_EVENT_MASTER_LINK_UP
- *              REDISMODULE_EVENT_MASTER_LINK_DOWN
+ *              REDISMODULE_SUBEVENT_MASTER_LINK_UP
+ *              REDISMODULE_SUBEVENT_MASTER_LINK_DOWN
+ *
+ *  RedisModuleEvent_ModuleChange
+ *
+ *          This event is called when a new module is loaded or one is unloaded.
+ *          The following sub events are availble:
+ *
+ *              REDISMODULE_SUBEVENT_MODULE_LOADED
+ *              REDISMODULE_SUBEVENT_MODULE_UNLOADED
+ *
+ *          The data pointer can be casted to a RedisModuleModuleChange
+ *          structure with the following fields:
+ *
+ *              const char* module_name;  // Name of module loaded or unloaded.
+ *              int32_t module_version;  // Module version.
+ *
+ *  RedisModuleEvent_LoadingProgress
+ *
+ *          This event is called repeatedly called while an RDB or AOF file
+ *          is being loaded.
+ *          The following sub events are availble:
+ *
+ *              REDISMODULE_SUBEVENT_LOADING_PROGRESS_RDB
+ *              REDISMODULE_SUBEVENT_LOADING_PROGRESS_AOF
+ *
+ *          The data pointer can be casted to a RedisModuleLoadingProgress
+ *          structure with the following fields:
+ *
+ *              int32_t hz;  // Approximate number of events per second.
+ *              int32_t progress;  // Approximate progress between 0 and 1024,
+ *                                    or -1 if unknown.
  *
  * The function returns REDISMODULE_OK if the module was successfully subscrived
  * for the specified event. If the API is called from a wrong context then
@@ -5954,7 +6019,7 @@ void moduleFireServerEvent(uint64_t eid, int subid, void *data) {
     listRewind(RedisModule_EventListeners,&li);
     while((ln = listNext(&li))) {
         RedisModuleEventListener *el = ln->value;
-        if (el->event.id == eid && !el->module->in_hook) {
+        if (el->event.id == eid) {
             RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
             ctx.module = el->module;
 
@@ -5968,6 +6033,8 @@ void moduleFireServerEvent(uint64_t eid, int subid, void *data) {
 
             void *moduledata = NULL;
             RedisModuleClientInfoV1 civ1;
+            RedisModuleReplicationInfoV1 riv1;
+            RedisModuleModuleChangeV1 mcv1;
             /* Start at DB zero by default when calling the handler. It's
              * up to the specific event setup to change it when it makes
              * sense. For instance for FLUSHDB events we select the correct
@@ -5979,11 +6046,26 @@ void moduleFireServerEvent(uint64_t eid, int subid, void *data) {
                 modulePopulateClientInfoStructure(&civ1,data,
                                                   el->event.dataver);
                 moduledata = &civ1;
+            } else if (eid == REDISMODULE_EVENT_REPLICATION_ROLE_CHANGED) {
+                modulePopulateReplicationInfoStructure(&riv1,el->event.dataver);
+                moduledata = &riv1;
             } else if (eid == REDISMODULE_EVENT_FLUSHDB) {
                 moduledata = data;
                 RedisModuleFlushInfoV1 *fi = data;
                 if (fi->dbnum != -1)
                     selectDb(ctx.client, fi->dbnum);
+            } else if (eid == REDISMODULE_EVENT_MODULE_CHANGE) {
+                RedisModule *m = data;
+                if (m == el->module)
+                    continue;
+                mcv1.version = REDISMODULE_MODULE_CHANGE_VERSION;
+                mcv1.module_name = m->name;
+                mcv1.module_version = m->ver;
+                moduledata = &mcv1;
+            } else if (eid == REDISMODULE_EVENT_LOADING_PROGRESS) {
+                moduledata = data;
+            } else if (eid == REDISMODULE_EVENT_CRON_LOOP) {
+                moduledata = data;
             }
 
             ModulesInHooks++;
@@ -6015,6 +6097,27 @@ void moduleUnsubscribeAllServerEvents(RedisModule *module) {
     }
 }
 
+void processModuleLoadingProgressEvent(int is_aof) {
+    long long now = ustime();
+    static long long next_event = 0;
+    if (now >= next_event) {
+        /* Fire the loading progress modules end event. */
+        int progress = -1;
+        if (server.loading_total_bytes)
+            progress = (server.loading_total_bytes<<10) / server.loading_total_bytes;
+        RedisModuleFlushInfoV1 fi = {REDISMODULE_LOADING_PROGRESS_VERSION,
+                                     server.hz,
+                                     progress};
+        moduleFireServerEvent(REDISMODULE_EVENT_LOADING_PROGRESS,
+                              is_aof?
+                                REDISMODULE_SUBEVENT_LOADING_PROGRESS_AOF:
+                                REDISMODULE_SUBEVENT_LOADING_PROGRESS_RDB,
+                              &fi);
+        /* decide when the next event should fire. */
+        next_event = now + 1000000 / server.hz;
+    }
+}
+
 /* --------------------------------------------------------------------------
  * Modules API internals
  * -------------------------------------------------------------------------- */
@@ -6183,6 +6286,11 @@ int moduleLoad(const char *path, void **module_argv, int module_argc) {
     ctx.module->blocked_clients = 0;
     ctx.module->handle = handle;
     serverLog(LL_NOTICE,"Module '%s' loaded from %s",ctx.module->name,path);
+    /* Fire the loaded modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_MODULE_CHANGE,
+                          REDISMODULE_SUBEVENT_MODULE_LOADED,
+                          ctx.module);
+
     moduleFreeContext(&ctx);
     return C_OK;
 }
@@ -6245,6 +6353,11 @@ int moduleUnload(sds name) {
             module->name, error);
     }
 
+    /* Fire the unloaded modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_MODULE_CHANGE,
+                          REDISMODULE_SUBEVENT_MODULE_UNLOADED,
+                          module);
+
     /* Remove from list of modules. */
     serverLog(LL_NOTICE,"Module %s unloaded",module->name);
     dictDelete(modules,module->name);
diff --git a/src/networking.c b/src/networking.c
index e7cc561fa..9336c177c 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -1118,6 +1118,11 @@ void freeClient(client *c) {
         if (c->flags & CLIENT_SLAVE && listLength(server.slaves) == 0)
             server.repl_no_slaves_since = server.unixtime;
         refreshGoodSlavesCount();
+        /* Fire the replica change modules event. */
+        if (c->replstate == SLAVE_STATE_ONLINE)
+            moduleFireServerEvent(REDISMODULE_EVENT_REPLICA_CHANGE,
+                                  REDISMODULE_SUBEVENT_REPLICA_CHANGE_OFFLINE,
+                                  NULL);
     }
 
     /* Master/slave cleanup Case 2:
diff --git a/src/rdb.c b/src/rdb.c
index f530219a4..b569edfea 100644
--- a/src/rdb.c
+++ b/src/rdb.c
@@ -1080,9 +1080,9 @@ ssize_t rdbSaveAuxFieldStrInt(rio *rdb, char *key, long long val) {
 }
 
 /* Save a few default AUX fields with information about the RDB generated. */
-int rdbSaveInfoAuxFields(rio *rdb, int flags, rdbSaveInfo *rsi) {
+int rdbSaveInfoAuxFields(rio *rdb, int rdbflags, rdbSaveInfo *rsi) {
     int redis_bits = (sizeof(void*) == 8) ? 64 : 32;
-    int aof_preamble = (flags & RDB_SAVE_AOF_PREAMBLE) != 0;
+    int aof_preamble = (rdbflags & RDBFLAGS_AOF_PREAMBLE) != 0;
 
     /* Add a few fields about the state when the RDB was created. */
     if (rdbSaveAuxFieldStrStr(rdb,"redis-ver",REDIS_VERSION) == -1) return -1;
@@ -1150,7 +1150,7 @@ ssize_t rdbSaveSingleModuleAux(rio *rdb, int when, moduleType *mt) {
  * When the function returns C_ERR and if 'error' is not NULL, the
  * integer pointed by 'error' is set to the value of errno just after the I/O
  * error. */
-int rdbSaveRio(rio *rdb, int *error, int flags, rdbSaveInfo *rsi) {
+int rdbSaveRio(rio *rdb, int *error, int rdbflags, rdbSaveInfo *rsi) {
     dictIterator *di = NULL;
     dictEntry *de;
     char magic[10];
@@ -1162,7 +1162,7 @@ int rdbSaveRio(rio *rdb, int *error, int flags, rdbSaveInfo *rsi) {
         rdb->update_cksum = rioGenericUpdateChecksum;
     snprintf(magic,sizeof(magic),"REDIS%04d",RDB_VERSION);
     if (rdbWriteRaw(rdb,magic,9) == -1) goto werr;
-    if (rdbSaveInfoAuxFields(rdb,flags,rsi) == -1) goto werr;
+    if (rdbSaveInfoAuxFields(rdb,rdbflags,rsi) == -1) goto werr;
     if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_BEFORE_RDB) == -1) goto werr;
 
     for (j = 0; j < server.dbnum; j++) {
@@ -1199,7 +1199,7 @@ int rdbSaveRio(rio *rdb, int *error, int flags, rdbSaveInfo *rsi) {
             /* When this RDB is produced as part of an AOF rewrite, move
              * accumulated diff from parent to child while rewriting in
              * order to have a smaller final write. */
-            if (flags & RDB_SAVE_AOF_PREAMBLE &&
+            if (rdbflags & RDBFLAGS_AOF_PREAMBLE &&
                 rdb->processed_bytes > processed+AOF_READ_DIFF_INTERVAL_BYTES)
             {
                 processed = rdb->processed_bytes;
@@ -1254,18 +1254,21 @@ werr:
 int rdbSaveRioWithEOFMark(rio *rdb, int *error, rdbSaveInfo *rsi) {
     char eofmark[RDB_EOF_MARK_SIZE];
 
+    startSaving(RDBFLAGS_REPLICATION);
     getRandomHexChars(eofmark,RDB_EOF_MARK_SIZE);
     if (error) *error = 0;
     if (rioWrite(rdb,"$EOF:",5) == 0) goto werr;
     if (rioWrite(rdb,eofmark,RDB_EOF_MARK_SIZE) == 0) goto werr;
     if (rioWrite(rdb,"\r\n",2) == 0) goto werr;
-    if (rdbSaveRio(rdb,error,RDB_SAVE_NONE,rsi) == C_ERR) goto werr;
+    if (rdbSaveRio(rdb,error,RDBFLAGS_NONE,rsi) == C_ERR) goto werr;
     if (rioWrite(rdb,eofmark,RDB_EOF_MARK_SIZE) == 0) goto werr;
+    stopSaving(1);
     return C_OK;
 
 werr: /* Write error. */
     /* Set 'error' only if not already set by rdbSaveRio() call. */
     if (error && *error == 0) *error = errno;
+    stopSaving(0);
     return C_ERR;
 }
 
@@ -1291,11 +1294,12 @@ int rdbSave(char *filename, rdbSaveInfo *rsi) {
     }
 
     rioInitWithFile(&rdb,fp);
+    startSaving(RDBFLAGS_NONE);
 
     if (server.rdb_save_incremental_fsync)
         rioSetAutoSync(&rdb,REDIS_AUTOSYNC_BYTES);
 
-    if (rdbSaveRio(&rdb,&error,RDB_SAVE_NONE,rsi) == C_ERR) {
+    if (rdbSaveRio(&rdb,&error,RDBFLAGS_NONE,rsi) == C_ERR) {
         errno = error;
         goto werr;
     }
@@ -1317,6 +1321,7 @@ int rdbSave(char *filename, rdbSaveInfo *rsi) {
             cwdp ? cwdp : "unknown",
             strerror(errno));
         unlink(tmpfile);
+        stopSaving(0);
         return C_ERR;
     }
 
@@ -1324,12 +1329,14 @@ int rdbSave(char *filename, rdbSaveInfo *rsi) {
     server.dirty = 0;
     server.lastsave = time(NULL);
     server.lastbgsave_status = C_OK;
+    stopSaving(1);
     return C_OK;
 
 werr:
     serverLog(LL_WARNING,"Write error saving DB on disk: %s", strerror(errno));
     fclose(fp);
     unlink(tmpfile);
+    stopSaving(0);
     return C_ERR;
 }
 
@@ -1918,23 +1925,33 @@ robj *rdbLoadObject(int rdbtype, rio *rdb, robj *key) {
 
 /* Mark that we are loading in the global state and setup the fields
  * needed to provide loading stats. */
-void startLoading(size_t size) {
+void startLoading(size_t size, int rdbflags) {
     /* Load the DB */
     server.loading = 1;
     server.loading_start_time = time(NULL);
     server.loading_loaded_bytes = 0;
     server.loading_total_bytes = size;
+
+    /* Fire the loading modules start event. */
+    int subevent;
+    if (rdbflags & RDBFLAGS_AOF_PREAMBLE)
+        subevent = REDISMODULE_SUBEVENT_LOADING_AOF_START;
+    else if(rdbflags & RDBFLAGS_REPLICATION)
+        subevent = REDISMODULE_SUBEVENT_LOADING_REPL_START;
+    else
+        subevent = REDISMODULE_SUBEVENT_LOADING_RDB_START;
+    moduleFireServerEvent(REDISMODULE_EVENT_LOADING,subevent,NULL);
 }
 
 /* Mark that we are loading in the global state and setup the fields
  * needed to provide loading stats.
  * 'filename' is optional and used for rdb-check on error */
-void startLoadingFile(FILE *fp, char* filename) {
+void startLoadingFile(FILE *fp, char* filename, int rdbflags) {
     struct stat sb;
     if (fstat(fileno(fp), &sb) == -1)
         sb.st_size = 0;
     rdbFileBeingLoaded = filename;
-    startLoading(sb.st_size);
+    startLoading(sb.st_size, rdbflags);
 }
 
 /* Refresh the loading progress info */
@@ -1945,9 +1962,37 @@ void loadingProgress(off_t pos) {
 }
 
 /* Loading finished */
-void stopLoading(void) {
+void stopLoading(int success) {
     server.loading = 0;
     rdbFileBeingLoaded = NULL;
+
+    /* Fire the loading modules end event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_LOADING,
+                          success?
+                            REDISMODULE_SUBEVENT_LOADING_ENDED:
+                            REDISMODULE_SUBEVENT_LOADING_FAILED,
+                          NULL);
+}
+
+void startSaving(int rdbflags) {
+    /* Fire the persistence modules end event. */
+    int subevent;
+    if (rdbflags & RDBFLAGS_AOF_PREAMBLE)
+        subevent = REDISMODULE_SUBEVENT_PERSISTENCE_AOF_START;
+    else if (getpid()!=server.pid)
+        subevent = REDISMODULE_SUBEVENT_PERSISTENCE_RDB_START;
+    else
+        subevent = REDISMODULE_SUBEVENT_PERSISTENCE_SYNC_RDB_START;
+    moduleFireServerEvent(REDISMODULE_EVENT_PERSISTENCE,subevent,NULL);
+}
+
+void stopSaving(int success) {
+    /* Fire the persistence modules end event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_PERSISTENCE,
+                          success?
+                            REDISMODULE_SUBEVENT_PERSISTENCE_ENDED:
+                            REDISMODULE_SUBEVENT_PERSISTENCE_FAILED,
+                          NULL);
 }
 
 /* Track loading progress in order to serve client's from time to time
@@ -1966,12 +2011,13 @@ void rdbLoadProgressCallback(rio *r, const void *buf, size_t len) {
             replicationSendNewlineToMaster();
         loadingProgress(r->processed_bytes);
         processEventsWhileBlocked();
+        processModuleLoadingProgressEvent(0);
     }
 }
 
 /* Load an RDB file from the rio stream 'rdb'. On success C_OK is returned,
  * otherwise C_ERR is returned and 'errno' is set accordingly. */
-int rdbLoadRio(rio *rdb, rdbSaveInfo *rsi, int loading_aof) {
+int rdbLoadRio(rio *rdb, int rdbflags, rdbSaveInfo *rsi) {
     uint64_t dbid;
     int type, rdbver;
     redisDb *db = server.db+0;
@@ -2182,7 +2228,7 @@ int rdbLoadRio(rio *rdb, rdbSaveInfo *rsi, int loading_aof) {
          * received from the master. In the latter case, the master is
          * responsible for key expiry. If we would expire keys here, the
          * snapshot taken by the master may not be reflected on the slave. */
-        if (server.masterhost == NULL && !loading_aof && expiretime != -1 && expiretime < now) {
+        if (server.masterhost == NULL && !(rdbflags&RDBFLAGS_AOF_PREAMBLE) && expiretime != -1 && expiretime < now) {
             decrRefCount(key);
             decrRefCount(val);
         } else {
@@ -2243,17 +2289,17 @@ eoferr:
  *
  * If you pass an 'rsi' structure initialied with RDB_SAVE_OPTION_INIT, the
  * loading code will fiil the information fields in the structure. */
-int rdbLoad(char *filename, rdbSaveInfo *rsi) {
+int rdbLoad(char *filename, rdbSaveInfo *rsi, int rdbflags) {
     FILE *fp;
     rio rdb;
     int retval;
 
     if ((fp = fopen(filename,"r")) == NULL) return C_ERR;
-    startLoadingFile(fp, filename);
+    startLoadingFile(fp, filename,rdbflags);
     rioInitWithFile(&rdb,fp);
-    retval = rdbLoadRio(&rdb,rsi,0);
+    retval = rdbLoadRio(&rdb,rdbflags,rsi);
     fclose(fp);
-    stopLoading();
+    stopLoading(retval==C_OK);
     return retval;
 }
 
diff --git a/src/rdb.h b/src/rdb.h
index 40a50f7ba..4229beea8 100644
--- a/src/rdb.h
+++ b/src/rdb.h
@@ -121,8 +121,10 @@
 #define RDB_LOAD_PLAIN  (1<<1)
 #define RDB_LOAD_SDS    (1<<2)
 
-#define RDB_SAVE_NONE 0
-#define RDB_SAVE_AOF_PREAMBLE (1<<0)
+/* flags on the purpose of rdb save or load */
+#define RDBFLAGS_NONE 0
+#define RDBFLAGS_AOF_PREAMBLE (1<<0)
+#define RDBFLAGS_REPLICATION (1<<1)
 
 int rdbSaveType(rio *rdb, unsigned char type);
 int rdbLoadType(rio *rdb);
@@ -135,7 +137,7 @@ uint64_t rdbLoadLen(rio *rdb, int *isencoded);
 int rdbLoadLenByRef(rio *rdb, int *isencoded, uint64_t *lenptr);
 int rdbSaveObjectType(rio *rdb, robj *o);
 int rdbLoadObjectType(rio *rdb);
-int rdbLoad(char *filename, rdbSaveInfo *rsi);
+int rdbLoad(char *filename, rdbSaveInfo *rsi, int rdbflags);
 int rdbSaveBackground(char *filename, rdbSaveInfo *rsi);
 int rdbSaveToSlavesSockets(rdbSaveInfo *rsi);
 void rdbRemoveTempFile(pid_t childpid);
@@ -154,7 +156,8 @@ int rdbSaveBinaryDoubleValue(rio *rdb, double val);
 int rdbLoadBinaryDoubleValue(rio *rdb, double *val);
 int rdbSaveBinaryFloatValue(rio *rdb, float val);
 int rdbLoadBinaryFloatValue(rio *rdb, float *val);
-int rdbLoadRio(rio *rdb, rdbSaveInfo *rsi, int loading_aof);
+int rdbLoadRio(rio *rdb, int rdbflags, rdbSaveInfo *rsi);
+int rdbSaveRio(rio *rdb, int *error, int rdbflags, rdbSaveInfo *rsi);
 rdbSaveInfo *rdbPopulateSaveInfo(rdbSaveInfo *rsi);
 
 #endif
diff --git a/src/redis-check-rdb.c b/src/redis-check-rdb.c
index 5e7415046..1210d49b4 100644
--- a/src/redis-check-rdb.c
+++ b/src/redis-check-rdb.c
@@ -202,7 +202,7 @@ int redis_check_rdb(char *rdbfilename, FILE *fp) {
     }
 
     expiretime = -1;
-    startLoadingFile(fp, rdbfilename);
+    startLoadingFile(fp, rdbfilename, RDBFLAGS_NONE);
     while(1) {
         robj *key, *val;
 
@@ -316,7 +316,7 @@ int redis_check_rdb(char *rdbfilename, FILE *fp) {
     }
 
     if (closefile) fclose(fp);
-    stopLoading();
+    stopLoading(1);
     return 0;
 
 eoferr: /* unexpected end of file is handled here with a fatal exit */
@@ -327,7 +327,7 @@ eoferr: /* unexpected end of file is handled here with a fatal exit */
     }
 err:
     if (closefile) fclose(fp);
-    stopLoading();
+    stopLoading(0);
     return 1;
 }
 
diff --git a/src/redismodule.h b/src/redismodule.h
index 7053840b2..7ae1ad692 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -181,6 +181,8 @@ typedef uint64_t RedisModuleTimerID;
 #define REDISMODULE_EVENT_REPLICA_CHANGE 6
 #define REDISMODULE_EVENT_MASTER_LINK_CHANGE 7
 #define REDISMODULE_EVENT_CRON_LOOP 8
+#define REDISMODULE_EVENT_MODULE_CHANGE 9
+#define REDISMODULE_EVENT_LOADING_PROGRESS 10
 
 typedef struct RedisModuleEvent {
     uint64_t id;        /* REDISMODULE_EVENT_... defines. */
@@ -226,18 +228,28 @@ static const RedisModuleEvent
     RedisModuleEvent_MasterLinkChange = {
         REDISMODULE_EVENT_MASTER_LINK_CHANGE,
         1
+    },
+    RedisModuleEvent_ModuleChange = {
+        REDISMODULE_EVENT_MODULE_CHANGE,
+        1
+    },
+    RedisModuleEvent_LoadingProgress = {
+        REDISMODULE_EVENT_LOADING_PROGRESS,
+        1
     };
 
 /* Those are values that are used for the 'subevent' callback argument. */
 #define REDISMODULE_SUBEVENT_PERSISTENCE_RDB_START 0
-#define REDISMODULE_SUBEVENT_PERSISTENCE_RDB_END 1
-#define REDISMODULE_SUBEVENT_PERSISTENCE_AOF_START 2
-#define REDISMODULE_SUBEVENT_PERSISTENCE_AOF_END 3
+#define REDISMODULE_SUBEVENT_PERSISTENCE_AOF_START 1
+#define REDISMODULE_SUBEVENT_PERSISTENCE_SYNC_RDB_START 2
+#define REDISMODULE_SUBEVENT_PERSISTENCE_ENDED 3
+#define REDISMODULE_SUBEVENT_PERSISTENCE_FAILED 4
 
 #define REDISMODULE_SUBEVENT_LOADING_RDB_START 0
-#define REDISMODULE_SUBEVENT_LOADING_RDB_END 1
-#define REDISMODULE_SUBEVENT_LOADING_AOF_START 2
-#define REDISMODULE_SUBEVENT_LOADING_AOF_END 3
+#define REDISMODULE_SUBEVENT_LOADING_AOF_START 1
+#define REDISMODULE_SUBEVENT_LOADING_REPL_START 2
+#define REDISMODULE_SUBEVENT_LOADING_ENDED 3
+#define REDISMODULE_SUBEVENT_LOADING_FAILED 4
 
 #define REDISMODULE_SUBEVENT_CLIENT_CHANGE_CONNECTED 0
 #define REDISMODULE_SUBEVENT_CLIENT_CHANGE_DISCONNECTED 1
@@ -245,12 +257,21 @@ static const RedisModuleEvent
 #define REDISMODULE_SUBEVENT_MASTER_LINK_UP 0
 #define REDISMODULE_SUBEVENT_MASTER_LINK_DOWN 1
 
-#define REDISMODULE_SUBEVENT_REPLICA_CHANGE_CONNECTED 0
-#define REDISMODULE_SUBEVENT_REPLICA_CHANGE_DISCONNECTED 1
+#define REDISMODULE_SUBEVENT_REPLICA_CHANGE_ONLINE 0
+#define REDISMODULE_SUBEVENT_REPLICA_CHANGE_OFFLINE 1
+
+#define REDISMODULE_EVENT_REPLROLECHANGED_NOW_MASTER 0
+#define REDISMODULE_EVENT_REPLROLECHANGED_NOW_REPLICA 1
 
 #define REDISMODULE_SUBEVENT_FLUSHDB_START 0
 #define REDISMODULE_SUBEVENT_FLUSHDB_END 1
 
+#define REDISMODULE_SUBEVENT_MODULE_LOADED 0
+#define REDISMODULE_SUBEVENT_MODULE_UNLOADED 1
+
+#define REDISMODULE_SUBEVENT_LOADING_PROGRESS_RDB 0
+#define REDISMODULE_SUBEVENT_LOADING_PROGRESS_AOF 1
+
 /* RedisModuleClientInfo flags. */
 #define REDISMODULE_CLIENTINFO_FLAG_SSL (1<<0)
 #define REDISMODULE_CLIENTINFO_FLAG_PUBSUB (1<<1)
@@ -286,6 +307,22 @@ typedef struct RedisModuleClientInfo {
 
 #define RedisModuleClientInfo RedisModuleClientInfoV1
 
+#define REDISMODULE_REPLICATIONINFO_VERSION 1
+typedef struct RedisModuleReplicationInfo {
+    uint64_t version;       /* Not used since this structure is never passed
+                               from the module to the core right now. Here
+                               for future compatibility. */
+    int master;             /* true if master, false if replica */
+    char *masterhost;       /* master instance hostname for NOW_REPLICA */
+    int masterport;         /* master instance port for NOW_REPLICA */
+    char *replid1;          /* Main replication ID */
+    char *replid2;          /* Secondary replication ID */
+    uint64_t repl1_offset;  /* Main replication offset */
+    uint64_t repl2_offset;  /* Offset of replid2 validity */
+} RedisModuleReplicationInfoV1;
+
+#define RedisModuleReplicationInfo RedisModuleReplicationInfoV1
+
 #define REDISMODULE_FLUSHINFO_VERSION 1
 typedef struct RedisModuleFlushInfo {
     uint64_t version;       /* Not used since this structure is never passed
@@ -297,6 +334,39 @@ typedef struct RedisModuleFlushInfo {
 
 #define RedisModuleFlushInfo RedisModuleFlushInfoV1
 
+#define REDISMODULE_MODULE_CHANGE_VERSION 1
+typedef struct RedisModuleModuleChange {
+    uint64_t version;       /* Not used since this structure is never passed
+                               from the module to the core right now. Here
+                               for future compatibility. */
+    const char* module_name;/* Name of module loaded or unloaded. */
+    int32_t module_version; /* Module version. */
+} RedisModuleModuleChangeV1;
+
+#define RedisModuleModuleChange RedisModuleModuleChangeV1
+
+#define REDISMODULE_CRON_LOOP_VERSION 1
+typedef struct RedisModuleCronLoopInfo {
+    uint64_t version;       /* Not used since this structure is never passed
+                               from the module to the core right now. Here
+                               for future compatibility. */
+    int32_t hz;             /* Approximate number of events per second. */
+} RedisModuleCronLoopV1;
+
+#define RedisModuleCronLoop RedisModuleCronLoopV1
+
+#define REDISMODULE_LOADING_PROGRESS_VERSION 1
+typedef struct RedisModuleLoadingProgressInfo {
+    uint64_t version;       /* Not used since this structure is never passed
+                               from the module to the core right now. Here
+                               for future compatibility. */
+    int32_t hz;             /* Approximate number of events per second. */
+    int32_t progress;       /* Approximate progress between 0 and 1024, or -1
+                             * if unknown. */
+} RedisModuleLoadingProgressV1;
+
+#define RedisModuleLoadingProgress RedisModuleLoadingProgressV1
+
 /* ------------------------- End of common defines ------------------------ */
 
 #ifndef REDISMODULE_CORE
diff --git a/src/replication.c b/src/replication.c
index 4550e6a83..c9a2e0fe1 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -533,6 +533,12 @@ int masterTryPartialResynchronization(client *c) {
      * has this state from the previous connection with the master. */
 
     refreshGoodSlavesCount();
+
+    /* Fire the replica change modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_REPLICA_CHANGE,
+                          REDISMODULE_SUBEVENT_REPLICA_CHANGE_ONLINE,
+                          NULL);
+
     return C_OK; /* The caller can return, no full resync needed. */
 
 need_full_resync:
@@ -868,6 +874,10 @@ void putSlaveOnline(client *slave) {
         return;
     }
     refreshGoodSlavesCount();
+    /* Fire the replica change modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_REPLICA_CHANGE,
+                          REDISMODULE_SUBEVENT_REPLICA_CHANGE_ONLINE,
+                          NULL);
     serverLog(LL_NOTICE,"Synchronization with replica %s succeeded",
         replicationGetSlaveName(slave));
 }
@@ -1542,11 +1552,11 @@ void readSyncBulkPayload(connection *conn) {
          * We'll restore it when the RDB is received. */
         connBlock(conn);
         connRecvTimeout(conn, server.repl_timeout*1000);
-        startLoading(server.repl_transfer_size);
+        startLoading(server.repl_transfer_size, RDBFLAGS_REPLICATION);
 
-        if (rdbLoadRio(&rdb,&rsi,0) != C_OK) {
+        if (rdbLoadRio(&rdb,RDBFLAGS_REPLICATION,&rsi) != C_OK) {
             /* RDB loading failed. */
-            stopLoading();
+            stopLoading(0);
             serverLog(LL_WARNING,
                 "Failed trying to load the MASTER synchronization DB "
                 "from socket");
@@ -1567,7 +1577,7 @@ void readSyncBulkPayload(connection *conn) {
              * gets promoted. */
             return;
         }
-        stopLoading();
+        stopLoading(1);
 
         /* RDB loading succeeded if we reach this point. */
         if (server.repl_diskless_load == REPL_DISKLESS_LOAD_SWAPDB) {
@@ -1614,7 +1624,7 @@ void readSyncBulkPayload(connection *conn) {
             cancelReplicationHandshake();
             return;
         }
-        if (rdbLoad(server.rdb_filename,&rsi) != C_OK) {
+        if (rdbLoad(server.rdb_filename,&rsi,RDBFLAGS_REPLICATION) != C_OK) {
             serverLog(LL_WARNING,
                 "Failed trying to load the MASTER synchronization "
                 "DB from disk");
@@ -1636,6 +1646,11 @@ void readSyncBulkPayload(connection *conn) {
     server.repl_state = REPL_STATE_CONNECTED;
     server.repl_down_since = 0;
 
+    /* Fire the master link modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_MASTER_LINK_CHANGE,
+                          REDISMODULE_SUBEVENT_MASTER_LINK_UP,
+                          NULL);
+
     /* After a full resynchroniziation we use the replication ID and
      * offset of the master. The secondary ID / offset are cleared since
      * we are starting a new history. */
@@ -2314,12 +2329,31 @@ void replicationSetMaster(char *ip, int port) {
         replicationDiscardCachedMaster();
         replicationCacheMasterUsingMyself();
     }
+
+    /* Fire the role change modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_REPLICATION_ROLE_CHANGED,
+                          REDISMODULE_EVENT_REPLROLECHANGED_NOW_REPLICA,
+                          NULL);
+
+    /* Fire the master link modules event. */
+    if (server.repl_state == REPL_STATE_CONNECTED)
+        moduleFireServerEvent(REDISMODULE_EVENT_MASTER_LINK_CHANGE,
+                              REDISMODULE_SUBEVENT_MASTER_LINK_DOWN,
+                              NULL);
+
     server.repl_state = REPL_STATE_CONNECT;
 }
 
 /* Cancel replication, setting the instance as a master itself. */
 void replicationUnsetMaster(void) {
     if (server.masterhost == NULL) return; /* Nothing to do. */
+
+    /* Fire the master link modules event. */
+    if (server.repl_state == REPL_STATE_CONNECTED)
+        moduleFireServerEvent(REDISMODULE_EVENT_MASTER_LINK_CHANGE,
+                              REDISMODULE_SUBEVENT_MASTER_LINK_DOWN,
+                              NULL);
+
     sdsfree(server.masterhost);
     server.masterhost = NULL;
     /* When a slave is turned into a master, the current replication ID
@@ -2348,11 +2382,22 @@ void replicationUnsetMaster(void) {
      * starting from now. Otherwise the backlog will be freed after a
      * failover if slaves do not connect immediately. */
     server.repl_no_slaves_since = server.unixtime;
+
+    /* Fire the role change modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_REPLICATION_ROLE_CHANGED,
+                          REDISMODULE_EVENT_REPLROLECHANGED_NOW_MASTER,
+                          NULL);
 }
 
 /* This function is called when the slave lose the connection with the
  * master into an unexpected way. */
 void replicationHandleMasterDisconnection(void) {
+    /* Fire the master link modules event. */
+    if (server.repl_state == REPL_STATE_CONNECTED)
+        moduleFireServerEvent(REDISMODULE_EVENT_MASTER_LINK_CHANGE,
+                              REDISMODULE_SUBEVENT_MASTER_LINK_DOWN,
+                              NULL);
+
     server.master = NULL;
     server.repl_state = REPL_STATE_CONNECT;
     server.repl_down_since = server.unixtime;
diff --git a/src/server.c b/src/server.c
index 8f165113d..f42924764 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2056,6 +2056,12 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
             server.rdb_bgsave_scheduled = 0;
     }
 
+    /* Fire the cron loop modules event. */
+    RedisModuleCronLoopV1 ei = {REDISMODULE_CRON_LOOP_VERSION,server.hz};
+    moduleFireServerEvent(REDISMODULE_EVENT_CRON_LOOP,
+                          0,
+                          &ei);
+
     server.cronloops++;
     return 1000/server.hz;
 }
@@ -3682,6 +3688,9 @@ int prepareForShutdown(int flags) {
         }
     }
 
+    /* Fire the shutdown modules event. */
+    moduleFireServerEvent(REDISMODULE_EVENT_SHUTDOWN,0,NULL);
+
     /* Remove the pid file if possible and needed. */
     if (server.daemonize || server.pidfile) {
         serverLog(LL_NOTICE,"Removing the pid file.");
@@ -4767,7 +4776,7 @@ void loadDataFromDisk(void) {
             serverLog(LL_NOTICE,"DB loaded from append only file: %.3f seconds",(float)(ustime()-start)/1000000);
     } else {
         rdbSaveInfo rsi = RDB_SAVE_INFO_INIT;
-        if (rdbLoad(server.rdb_filename,&rsi) == C_OK) {
+        if (rdbLoad(server.rdb_filename,&rsi,RDBFLAGS_NONE) == C_OK) {
             serverLog(LL_NOTICE,"DB loaded from disk: %.3f seconds",
                 (float)(ustime()-start)/1000000);
 
diff --git a/src/server.h b/src/server.h
index 97672d727..b52d57a05 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1602,6 +1602,7 @@ ssize_t rdbSaveModulesAux(rio *rdb, int when);
 int moduleAllDatatypesHandleErrors();
 sds modulesCollectInfo(sds info, sds section, int for_crash_report, int sections);
 void moduleFireServerEvent(uint64_t eid, int subid, void *data);
+void processModuleLoadingProgressEvent(int is_aof);
 
 /* Utils */
 long long ustime(void);
@@ -1831,10 +1832,12 @@ void rdbPipeReadHandler(struct aeEventLoop *eventLoop, int fd, void *clientData,
 void rdbPipeWriteHandlerConnRemoved(struct connection *conn);
 
 /* Generic persistence functions */
-void startLoadingFile(FILE* fp, char* filename);
-void startLoading(size_t size);
+void startLoadingFile(FILE* fp, char* filename, int rdbflags);
+void startLoading(size_t size, int rdbflags);
 void loadingProgress(off_t pos);
-void stopLoading(void);
+void stopLoading(int success);
+void startSaving(int rdbflags);
+void stopSaving(int success);
 
 #define DISK_ERROR_TYPE_AOF 1       /* Don't accept writes: AOF errors. */
 #define DISK_ERROR_TYPE_RDB 2       /* Don't accept writes: RDB errors. */
@@ -1843,7 +1846,6 @@ int writeCommandsDeniedByDiskError(void);
 
 /* RDB persistence */
 #include "rdb.h"
-int rdbSaveRio(rio *rdb, int *error, int flags, rdbSaveInfo *rsi);
 void killRDBChild(void);
 
 /* AOF persistence */
diff --git a/tests/modules/hooks.c b/tests/modules/hooks.c
index 33b690b2f..665a20481 100644
--- a/tests/modules/hooks.c
+++ b/tests/modules/hooks.c
@@ -30,36 +30,227 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#define REDISMODULE_EXPERIMENTAL_API
 #include "redismodule.h"
+#include <stdio.h>
+#include <string.h>
+
+/* We need to store events to be able to test and see what we got, and we can't
+ * store them in the key-space since that would mess up rdb loading (duplicates)
+ * and be lost of flushdb. */
+RedisModuleDict *event_log = NULL;
+
+typedef struct EventElement {
+    long count;
+    RedisModuleString *last_val_string;
+    long last_val_int;
+} EventElement;
+
+void LogStringEvent(RedisModuleCtx *ctx, const char* keyname, const char* data) {
+    EventElement *event = RedisModule_DictGetC(event_log, (void*)keyname, strlen(keyname), NULL);
+    if (!event) {
+        event = RedisModule_Alloc(sizeof(EventElement));
+        memset(event, 0, sizeof(EventElement));
+        RedisModule_DictSetC(event_log, (void*)keyname, strlen(keyname), event);
+    }
+    if (event->last_val_string) RedisModule_FreeString(ctx, event->last_val_string);
+    event->last_val_string = RedisModule_CreateString(ctx, data, strlen(data));
+    event->count++;
+}
+
+void LogNumericEvent(RedisModuleCtx *ctx, const char* keyname, long data) {
+    REDISMODULE_NOT_USED(ctx);
+    EventElement *event = RedisModule_DictGetC(event_log, (void*)keyname, strlen(keyname), NULL);
+    if (!event) {
+        event = RedisModule_Alloc(sizeof(EventElement));
+        memset(event, 0, sizeof(EventElement));
+        RedisModule_DictSetC(event_log, (void*)keyname, strlen(keyname), event);
+    }
+    event->last_val_int = data;
+    event->count++;
+}
+
+void FreeEvent(RedisModuleCtx *ctx, EventElement *event) {
+    if (event->last_val_string)
+        RedisModule_FreeString(ctx, event->last_val_string);
+    RedisModule_Free(event);
+}
+
+int cmdEventCount(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    if (argc != 2){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+
+    EventElement *event = RedisModule_DictGet(event_log, argv[1], NULL);
+    RedisModule_ReplyWithLongLong(ctx, event? event->count: 0);
+    return REDISMODULE_OK;
+}
+
+int cmdEventLast(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    if (argc != 2){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+
+    EventElement *event = RedisModule_DictGet(event_log, argv[1], NULL);
+    if (event && event->last_val_string)
+        RedisModule_ReplyWithString(ctx, event->last_val_string);
+    else if (event)
+        RedisModule_ReplyWithLongLong(ctx, event->last_val_int);
+    else
+        RedisModule_ReplyWithNull(ctx);
+    return REDISMODULE_OK;
+}
+
+void clearEvents(RedisModuleCtx *ctx)
+{
+    RedisModuleString *key;
+    EventElement *event;
+    RedisModuleDictIter *iter = RedisModule_DictIteratorStart(event_log, "^", NULL);
+    while((key = RedisModule_DictNext(ctx, iter, (void**)&event)) != NULL) {
+        event->count = 0;
+        event->last_val_int = 0;
+        if (event->last_val_string) RedisModule_FreeString(ctx, event->last_val_string);
+        event->last_val_string = NULL;
+        RedisModule_DictDel(event_log, key, NULL);
+        RedisModule_Free(event);
+    }
+    RedisModule_DictIteratorStop(iter);
+}
+
+int cmdEventsClear(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    REDISMODULE_NOT_USED(argc);
+    REDISMODULE_NOT_USED(argv);
+    clearEvents(ctx);
+    return REDISMODULE_OK;
+}
 
 /* Client state change callback. */
 void clientChangeCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
 {
-    REDISMODULE_NOT_USED(ctx);
     REDISMODULE_NOT_USED(e);
 
     RedisModuleClientInfo *ci = data;
     char *keyname = (sub == REDISMODULE_SUBEVENT_CLIENT_CHANGE_CONNECTED) ?
-        "connected" : "disconnected";
-    RedisModuleCallReply *reply;
-    RedisModule_SelectDb(ctx,9);
-    reply = RedisModule_Call(ctx,"RPUSH","cl",keyname,(long)ci->id);
-    RedisModule_FreeCallReply(reply);
+        "client-connected" : "client-disconnected";
+    LogNumericEvent(ctx, keyname, ci->id);
 }
 
 void flushdbCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
 {
-    REDISMODULE_NOT_USED(ctx);
     REDISMODULE_NOT_USED(e);
 
     RedisModuleFlushInfo *fi = data;
     char *keyname = (sub == REDISMODULE_SUBEVENT_FLUSHDB_START) ?
         "flush-start" : "flush-end";
-    RedisModuleCallReply *reply;
-    RedisModule_SelectDb(ctx,9);
-    reply = RedisModule_Call(ctx,"RPUSH","cl",keyname,(long)fi->dbnum);
-    RedisModule_FreeCallReply(reply);
+    LogNumericEvent(ctx, keyname, fi->dbnum);
+}
+
+void roleChangeCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(data);
+
+    RedisModuleReplicationInfo *ri = data;
+    char *keyname = (sub == REDISMODULE_EVENT_REPLROLECHANGED_NOW_MASTER) ?
+        "role-master" : "role-replica";
+    LogStringEvent(ctx, keyname, ri->masterhost);
+}
+
+void replicationChangeCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(data);
+
+    char *keyname = (sub == REDISMODULE_SUBEVENT_REPLICA_CHANGE_ONLINE) ?
+        "replica-online" : "replica-offline";
+    LogNumericEvent(ctx, keyname, 0);
+}
+
+void rasterLinkChangeCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(data);
+
+    char *keyname = (sub == REDISMODULE_SUBEVENT_MASTER_LINK_UP) ?
+        "masterlink-up" : "masterlink-down";
+    LogNumericEvent(ctx, keyname, 0);
+}
+
+void persistenceCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(data);
+
+    char *keyname = NULL;
+    switch (sub) {
+        case REDISMODULE_SUBEVENT_PERSISTENCE_RDB_START: keyname = "persistence-rdb-start"; break;
+        case REDISMODULE_SUBEVENT_PERSISTENCE_AOF_START: keyname = "persistence-aof-start"; break;
+        case REDISMODULE_SUBEVENT_PERSISTENCE_SYNC_RDB_START: keyname = "persistence-syncrdb-start"; break;
+        case REDISMODULE_SUBEVENT_PERSISTENCE_ENDED: keyname = "persistence-end"; break;
+        case REDISMODULE_SUBEVENT_PERSISTENCE_FAILED: keyname = "persistence-failed"; break;
+    }
+    /* modifying the keyspace from the fork child is not an option, using log instead */
+    RedisModule_Log(ctx, "warning", "module-event-%s", keyname);
+    if (sub == REDISMODULE_SUBEVENT_PERSISTENCE_SYNC_RDB_START)
+        LogNumericEvent(ctx, keyname, 0);
+}
+
+void loadingCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(data);
+
+    char *keyname = NULL;
+    switch (sub) {
+        case REDISMODULE_SUBEVENT_LOADING_RDB_START: keyname = "loading-rdb-start"; break;
+        case REDISMODULE_SUBEVENT_LOADING_AOF_START: keyname = "loading-aof-start"; break;
+        case REDISMODULE_SUBEVENT_LOADING_REPL_START: keyname = "loading-repl-start"; break;
+        case REDISMODULE_SUBEVENT_LOADING_ENDED: keyname = "loading-end"; break;
+        case REDISMODULE_SUBEVENT_LOADING_FAILED: keyname = "loading-failed"; break;
+    }
+    LogNumericEvent(ctx, keyname, 0);
+}
+
+void loadingProgressCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+
+    RedisModuleLoadingProgress *ei = data;
+    char *keyname = (sub == REDISMODULE_SUBEVENT_LOADING_PROGRESS_RDB) ?
+        "loading-progress-rdb" : "loading-progress-aof";
+    LogNumericEvent(ctx, keyname, ei->progress);
+}
+
+void shutdownCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(data);
+    REDISMODULE_NOT_USED(sub);
+
+    RedisModule_Log(ctx, "warning", "module-event-%s", "shutdown");
+}
+
+void cronLoopCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+    REDISMODULE_NOT_USED(sub);
+
+    RedisModuleCronLoop *ei = data;
+    LogNumericEvent(ctx, "cron-loop", ei->hz);
+}
+
+void moduleChangeCallback(RedisModuleCtx *ctx, RedisModuleEvent e, uint64_t sub, void *data)
+{
+    REDISMODULE_NOT_USED(e);
+
+    RedisModuleModuleChange *ei = data;
+    char *keyname = (sub == REDISMODULE_SUBEVENT_MODULE_LOADED) ?
+        "module-loaded" : "module-unloaded";
+    LogStringEvent(ctx, keyname, ei->module_name);
 }
 
 /* This function must be present on each Redis module. It is used in order to
@@ -71,9 +262,50 @@ int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
     if (RedisModule_Init(ctx,"testhook",1,REDISMODULE_APIVER_1)
         == REDISMODULE_ERR) return REDISMODULE_ERR;
 
+    /* replication related hooks */
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_ReplicationRoleChanged, roleChangeCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_ReplicaChange, replicationChangeCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_MasterLinkChange, rasterLinkChangeCallback);
+
+    /* persistence related hooks */
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_Persistence, persistenceCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_Loading, loadingCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_LoadingProgress, loadingProgressCallback);
+
+    /* other hooks */
     RedisModule_SubscribeToServerEvent(ctx,
         RedisModuleEvent_ClientChange, clientChangeCallback);
     RedisModule_SubscribeToServerEvent(ctx,
         RedisModuleEvent_FlushDB, flushdbCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_Shutdown, shutdownCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_CronLoop, cronLoopCallback);
+    RedisModule_SubscribeToServerEvent(ctx,
+        RedisModuleEvent_ModuleChange, moduleChangeCallback);
+
+    event_log = RedisModule_CreateDict(ctx);
+
+    if (RedisModule_CreateCommand(ctx,"hooks.event_count", cmdEventCount,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+    if (RedisModule_CreateCommand(ctx,"hooks.event_last", cmdEventLast,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+    if (RedisModule_CreateCommand(ctx,"hooks.clear", cmdEventsClear,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
     return REDISMODULE_OK;
 }
+
+int RedisModule_OnUnload(RedisModuleCtx *ctx) {
+    clearEvents(ctx);
+    RedisModule_FreeDict(ctx, event_log);
+    event_log = NULL;
+    return REDISMODULE_OK;
+}
+
diff --git a/tests/unit/moduleapi/hooks.tcl b/tests/unit/moduleapi/hooks.tcl
index 7a727902d..cbca9c3eb 100644
--- a/tests/unit/moduleapi/hooks.tcl
+++ b/tests/unit/moduleapi/hooks.tcl
@@ -3,26 +3,138 @@ set testmodule [file normalize tests/modules/hooks.so]
 tags "modules" {
     start_server {} {
         r module load $testmodule
+        r config set appendonly yes
+
         test {Test clients connection / disconnection hooks} {
             for {set j 0} {$j < 2} {incr j} {
                 set rd1 [redis_deferring_client]
                 $rd1 close
             }
-            assert {[r llen connected] > 1}
-            assert {[r llen disconnected] > 1}
+            assert {[r hooks.event_count client-connected] > 1}
+            assert {[r hooks.event_count client-disconnected] > 1}
+        }
+
+        test {Test module cron hook} {
+            after 100
+            assert {[r hooks.event_count cron-loop] > 0}
+            set hz [r hooks.event_last cron-loop]
+            assert_equal $hz 10
+        }
+
+        test {Test module loaded / unloaded hooks} {
+            set othermodule [file normalize tests/modules/infotest.so]
+            r module load $othermodule
+            r module unload infotest
+            assert_equal [r hooks.event_last module-loaded] "infotest"
+            assert_equal [r hooks.event_last module-unloaded] "infotest"
+        }
+
+        test {Test module aofrw hook} {
+            r debug populate 1000 foo 10000 ;# 10mb worth of data
+            r config set rdbcompression no ;# rdb progress is only checked once in 2mb
+            r BGREWRITEAOF
+            waitForBgrewriteaof r
+            assert_equal [string match {*module-event-persistence-aof-start*} [exec tail -20 < [srv 0 stdout]]] 1
+            assert_equal [string match {*module-event-persistence-end*} [exec tail -20 < [srv 0 stdout]]] 1
+        }
+
+        test {Test module aof load and rdb/aof progress hooks} {
+            # create some aof tail (progress is checked only once in 1000 commands)
+            for {set j 0} {$j < 4000} {incr j} {
+                r set "bar$j" x
+            }
+            # set some configs that will cause many loading progress events during aof loading
+            r config set key-load-delay 1
+            r config set dynamic-hz no
+            r config set hz 500
+            r DEBUG LOADAOF
+            assert_equal [r hooks.event_last loading-aof-start] 0
+            assert_equal [r hooks.event_last loading-end] 0
+            assert {[r hooks.event_count loading-rdb-start] == 0}
+            assert {[r hooks.event_count loading-progress-rdb] >= 2} ;# comes from the preamble section
+            assert {[r hooks.event_count loading-progress-aof] >= 2}
+        }
+        # undo configs before next test
+        r config set dynamic-hz yes
+        r config set key-load-delay 0
+
+        test {Test module rdb save hook} {
+            # debug reload does: save, flush, load:
+            assert {[r hooks.event_count persistence-syncrdb-start] == 0}
+            assert {[r hooks.event_count loading-rdb-start] == 0}
+            r debug reload
+            assert {[r hooks.event_count persistence-syncrdb-start] == 1}
+            assert {[r hooks.event_count loading-rdb-start] == 1}
         }
 
         test {Test flushdb hooks} {
-            r flushall ;# Note: only the "end" RPUSH will survive
-            r select 1
             r flushdb
-            r select 2
-            r flushdb
-            r select 9
-            assert {[r llen flush-start] == 2}
-            assert {[r llen flush-end] == 3}
-            assert {[r lrange flush-start 0 -1] eq {1 2}}
-            assert {[r lrange flush-end 0 -1] eq {-1 1 2}}
+            assert_equal [r hooks.event_last flush-start] 9
+            assert_equal [r hooks.event_last flush-end] 9
+            r flushall
+            assert_equal [r hooks.event_last flush-start] -1
+            assert_equal [r hooks.event_last flush-end] -1
         }
+
+        # replication related tests
+        set master [srv 0 client]
+        set master_host [srv 0 host]
+        set master_port [srv 0 port]
+        start_server {} {
+            r module load $testmodule
+            set replica [srv 0 client]
+            set replica_host [srv 0 host]
+            set replica_port [srv 0 port]
+            $replica replicaof $master_host $master_port
+
+            wait_for_condition 50 100 {
+                [string match {*master_link_status:up*} [r info replication]]
+            } else {
+                fail "Can't turn the instance into a replica"
+            }
+
+            test {Test master link up hook} {
+                assert_equal [r hooks.event_count masterlink-up] 1
+                assert_equal [r hooks.event_count masterlink-down] 0
+            }
+
+            test {Test role-replica hook} {
+                assert_equal [r hooks.event_count role-replica] 1
+                assert_equal [r hooks.event_count role-master] 0
+                assert_equal [r hooks.event_last role-replica] [s 0 master_host]
+            }
+
+            test {Test replica-online hook} {
+                assert_equal [r -1 hooks.event_count replica-online] 1
+                assert_equal [r -1 hooks.event_count replica-offline] 0
+            }
+
+            test {Test master link down hook} {
+                r client kill type master
+                assert_equal [r hooks.event_count masterlink-down] 1
+            }
+
+            $replica replicaof no one
+
+            test {Test role-master hook} {
+                assert_equal [r hooks.event_count role-replica] 1
+                assert_equal [r hooks.event_count role-master] 1
+                assert_equal [r hooks.event_last role-master] {}
+            }
+
+            test {Test replica-offline hook} {
+                assert_equal [r -1 hooks.event_count replica-online] 1
+                assert_equal [r -1 hooks.event_count replica-offline] 1
+            }
+            # get the replica stdout, to be used by the next test
+            set replica_stdout [srv 0 stdout]
+        }
+
+
+        # look into the log file of the server that just exited
+        test {Test shutdown hook} {
+            assert_equal [string match {*module-event-shutdown*} [exec tail -5 < $replica_stdout]] 1
+        }
+
     }
 }

From 3649568ff22dbb6ea3e26c722d115ba5635547ae Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Wed, 30 Oct 2019 10:11:58 +0100
Subject: [PATCH 02/15] Modules: block on keys functions layout and mechanism.

---
 src/module.c | 153 ++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 120 insertions(+), 33 deletions(-)

diff --git a/src/module.c b/src/module.c
index 971bf5c08..bdafc1590 100644
--- a/src/module.c
+++ b/src/module.c
@@ -245,6 +245,15 @@ typedef struct RedisModuleBlockedClient {
     client *reply_client;           /* Fake client used to accumulate replies
                                        in thread safe contexts. */
     int dbid;           /* Database number selected by the original client. */
+    int blocked_on_keys;    /* If blocked via RM_BlockClientOnKeys(). */
+    int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *keyname,
+                        void *privdata);  /* When blocking on keys, even if the
+                                             key is signaled as ready, maybe it
+                                             was modified afterward before the
+                                             client unblocks. So we always
+                                             need a callback that tells us if
+                                             the key is ready in order to serve
+                                             the next blocked client. */
 } RedisModuleBlockedClient;
 
 static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
@@ -3989,6 +3998,68 @@ void unblockClientFromModule(client *c) {
     resetClient(c);
 }
 
+/* Block a client in the context of a module: this function implements both
+ * RM_BlockClient() and RM_BlockClientOnKeys() depending on the fact the
+ * keys are passed or not.
+ *
+ * When not blocking for keys, the keys, numkeys, is_key_ready callback
+ * and privdata parameters are not needed. The privdata in that case must
+ * be NULL, since later is RM_UnblockClient() that will provide some private
+ * data that the reply callback will receive.
+ *
+ * Instead when blocking for keys, normally RM_UnblockClient() will not be
+ * called (because the client will unblock when the key is modified), so
+ * 'privdata' should be provided in that case, so that once the client is
+ * unlocked and the reply callback is called, it will receive its associated
+ * private data.
+ *
+ * Even when blocking on keys, RM_UnblockClient() can be called however, but
+ * in that case the privdata argument is disregarded, because we pass the
+ * reply callback the privdata that is set here while blocking.
+ */
+RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *key, void *privdata), void *privdata) {
+    client *c = ctx->client;
+    int islua = c->flags & CLIENT_LUA;
+    int ismulti = c->flags & CLIENT_MULTI;
+
+    c->bpop.module_blocked_handle = zmalloc(sizeof(RedisModuleBlockedClient));
+    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
+    ctx->module->blocked_clients++;
+
+    /* We need to handle the invalid operation of calling modules blocking
+     * commands from Lua or MULTI. We actually create an already aborted
+     * (client set to NULL) blocked client handle, and actually reply with
+     * an error. */
+    mstime_t timeout = timeout_ms ? (mstime()+timeout_ms) : 0;
+    bc->client = (islua || ismulti) ? NULL : c;
+    bc->module = ctx->module;
+    bc->reply_callback = reply_callback;
+    bc->timeout_callback = timeout_callback;
+    bc->disconnect_callback = NULL; /* Set by RM_SetDisconnectCallback() */
+    bc->free_privdata = free_privdata;
+    bc->privdata = privdata;
+    bc->reply_client = createClient(NULL);
+    bc->reply_client->flags |= CLIENT_MODULE;
+    bc->dbid = c->db->id;
+    bc->is_key_ready = is_key_ready;
+    bc->blocked_on_keys = keys != NULL;
+    c->bpop.timeout = timeout;
+
+    if (islua || ismulti) {
+        c->bpop.module_blocked_handle = NULL;
+        addReplyError(c, islua ?
+            "Blocking module command called from Lua script" :
+            "Blocking module command called from transaction");
+    } else {
+        if (keys) {
+            blockForKeys(c,BLOCKED_MODULE,keys,numkeys,timeout,NULL,NULL);
+        } else {
+            blockClient(c,BLOCKED_MODULE);
+        }
+    }
+    return bc;
+}
+
 /* Block a client in the context of a blocking command, returning an handle
  * which will be used, later, in order to unblock the client with a call to
  * RedisModule_UnblockClient(). The arguments specify callback functions
@@ -4006,39 +4077,55 @@ void unblockClientFromModule(client *c) {
  *                      by RedisModule_UnblockClient() call.
  */
 RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms) {
-    client *c = ctx->client;
-    int islua = c->flags & CLIENT_LUA;
-    int ismulti = c->flags & CLIENT_MULTI;
+    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, NULL,0,NULL,NULL);
+}
 
-    c->bpop.module_blocked_handle = zmalloc(sizeof(RedisModuleBlockedClient));
-    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
-    ctx->module->blocked_clients++;
-
-    /* We need to handle the invalid operation of calling modules blocking
-     * commands from Lua or MULTI. We actually create an already aborted
-     * (client set to NULL) blocked client handle, and actually reply with
-     * an error. */
-    bc->client = (islua || ismulti) ? NULL : c;
-    bc->module = ctx->module;
-    bc->reply_callback = reply_callback;
-    bc->timeout_callback = timeout_callback;
-    bc->disconnect_callback = NULL; /* Set by RM_SetDisconnectCallback() */
-    bc->free_privdata = free_privdata;
-    bc->privdata = NULL;
-    bc->reply_client = createClient(NULL);
-    bc->reply_client->flags |= CLIENT_MODULE;
-    bc->dbid = c->db->id;
-    c->bpop.timeout = timeout_ms ? (mstime()+timeout_ms) : 0;
-
-    if (islua || ismulti) {
-        c->bpop.module_blocked_handle = NULL;
-        addReplyError(c, islua ?
-            "Blocking module command called from Lua script" :
-            "Blocking module command called from transaction");
-    } else {
-        blockClient(c,BLOCKED_MODULE);
-    }
-    return bc;
+/* This call is similar to RedisModule_BlockClient(), however in this case we
+ * don't just block the client, but also ask Redis to unblock it automatically
+ * once certain keys become "ready", that is, contain more data.
+ *
+ * Basically this is similar to what a typical Redis command usually does,
+ * like BLPOP or ZPOPMAX: the client blocks if it cannot be served ASAP,
+ * and later when the key receives new data (a list push for instance), the
+ * client is unblocked and served.
+ *
+ * However in the case of this module API, when the client is unblocked?
+ *
+ * 1. If you block ok a key of a type that has blocking operations associated,
+ *    like a list, a sorted set, a stream, and so forth, the client may be
+ *    unblocked once the relevant key is targeted by an operation that normally
+ *    unblocks the native blocking operations for that type. So if we block
+ *    on a list key, an RPUSH command may unblock our client and so forth.
+ * 2. If you are implementing your native data type, or if you want to add new
+ *    unblocking conditions in addition to "1", you can call the modules API
+ *    RedisModule_SignalKeyAsReady().
+ *
+ * Anyway we can't be sure if the client should be unblocked just because the
+ * key is signaled as ready: for instance a successive operation may change the
+ * key, or a client in queue before this one can be served, modifying the key
+ * as well and making it empty again. So when blocking for keys, we need to
+ * register a callback called is_key_ready. This callback gets called with
+ * a context, selected with the right database, and the key name: if it
+ * returns 1, then we proceed calling the reply callback, otherwise if the
+ * is_key_ready callback returns 0 the client is not unblocked, since the
+ * key is yet not ready.
+ *
+ * Thanks to this system we can setup complex blocking scenarios, like
+ * unblocking a client only if a list contains at least 5 items or other
+ * more fancy logics.
+ *
+ * Note that another difference with RedisModule_BlockClient(), is that here
+ * we pass the private data directly when blocking the client: such private
+ * data will be later provided both to the is_key_ready callback, and to the
+ * reply callback. Normally in RedisModule_BlockClient() the private data
+ * to reply to the client is passed when calling RedisModule_UnblockClient()
+ * but here the unblocking is performed by Redis itself, so we need to have
+ * some private data before hand. The private data is used to store any
+ * information about the specific unblocking operation that you are
+ * implementing. Such information will be freed using the free_privdata
+ * callback provided by the user. */
+RedisModuleBlockedClient *RM_BlockClientOnKeys(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *keyname, void *privdata), void *privdata) {
+    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,is_key_ready,privdata);
 }
 
 /* Unblock a client blocked by `RedisModule_BlockedClient`. This will trigger
@@ -4054,7 +4141,7 @@ RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc
  * Note: this function can be called from threads spawned by the module. */
 int RM_UnblockClient(RedisModuleBlockedClient *bc, void *privdata) {
     pthread_mutex_lock(&moduleUnblockedClientsMutex);
-    bc->privdata = privdata;
+    if (!bc->blocked_on_keys) bc->privdata = privdata;
     listAddNodeTail(moduleUnblockedClients,bc);
     if (write(server.module_blocked_pipe[1],"A",1) != 1) {
         /* Ignore the error, this is best-effort. */

From fb6110ac2062a548aa79c9bb5f11e3fa10e71ba2 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Wed, 30 Oct 2019 10:20:28 +0100
Subject: [PATCH 03/15] Modules: block on keys: export APIs.

---
 src/module.c      | 11 +++++++++++
 src/redismodule.h |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/src/module.c b/src/module.c
index bdafc1590..113375e75 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4128,6 +4128,15 @@ RedisModuleBlockedClient *RM_BlockClientOnKeys(RedisModuleCtx *ctx, RedisModuleC
     return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,is_key_ready,privdata);
 }
 
+/* This function is used in order to potentially unblock a client blocked
+ * on keys with RedisModule_BlockClientOnKeys(). When this function is called,
+ * all the clients blocked for this key will get their is_key_ready callback,
+ * and if the callback returns non-zero the client will be unblocked and the
+ * reply callback will be called in order to reply to the client. */
+void RM_SignalKeyAsReady(RedisModuleCtx *ctx, RedisModuleString *key) {
+    signalKeyAsReady(ctx->client->db, key);
+}
+
 /* Unblock a client blocked by `RedisModule_BlockedClient`. This will trigger
  * the reply callbacks to be called in order to reply to the client.
  * The 'privdata' argument will be accessible by the reply callback, so
@@ -6634,4 +6643,6 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(InfoAddFieldULongLong);
     REGISTER_API(GetClientInfoById);
     REGISTER_API(SubscribeToServerEvent);
+    REGISTER_API(BlockClientOnKeys);
+    REGISTER_API(SignalKeyAsReady);
 }
diff --git a/src/redismodule.h b/src/redismodule.h
index 4b63a227c..5b4c31b19 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -492,6 +492,8 @@ int REDISMODULE_API_FUNC(RedisModule_InfoAddFieldDouble)(RedisModuleInfoCtx *ctx
 int REDISMODULE_API_FUNC(RedisModule_InfoAddFieldLongLong)(RedisModuleInfoCtx *ctx, char *field, long long value);
 int REDISMODULE_API_FUNC(RedisModule_InfoAddFieldULongLong)(RedisModuleInfoCtx *ctx, char *field, unsigned long long value);
 int REDISMODULE_API_FUNC(RedisModule_SubscribeToServerEvent)(RedisModuleCtx *ctx, RedisModuleEvent event, RedisModuleEventCallback callback);
+RedisModuleBlockedClient *REDISMODULE_API_FUNC(RedisModule_BlockClientOnKeys)(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *keyname, void *privdata), void *privdata);
+void REDISMODULE_API_FUNC(RedisModule_SignalKeyAsReady)(RedisModuleCtx *ctx, RedisModuleString *key);
 
 /* Experimental APIs */
 #ifdef REDISMODULE_EXPERIMENTAL_API
@@ -688,6 +690,8 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(InfoAddFieldULongLong);
     REDISMODULE_GET_API(GetClientInfoById);
     REDISMODULE_GET_API(SubscribeToServerEvent);
+    REDISMODULE_GET_API(BlockClientOnKeys);
+    REDISMODULE_GET_API(SignalKeyAsReady);
 
 #ifdef REDISMODULE_EXPERIMENTAL_API
     REDISMODULE_GET_API(GetThreadSafeContext);

From 215b72c0ba1f42d15dcfe6fa60abb414275296ba Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Wed, 30 Oct 2019 10:57:44 +0100
Subject: [PATCH 04/15] Modules: block on keys: implement the internals.

---
 src/blocked.c | 30 ++++++++++++++++++++++++++++
 src/module.c  | 54 +++++++++++++++++++++++++++++++++++++++++++--------
 src/server.h  |  2 ++
 3 files changed, 78 insertions(+), 8 deletions(-)

diff --git a/src/blocked.c b/src/blocked.c
index 867f03de6..2b91c1b44 100644
--- a/src/blocked.c
+++ b/src/blocked.c
@@ -430,6 +430,32 @@ void serveClientsBlockedOnStreamKey(robj *o, readyList *rl) {
     }
 }
 
+/* Helper function for handleClientsBlockedOnKeys(). This function is called
+ * in order to check if we can serve clients blocked by modules using
+ * RM_BlockClientOnKeys(), when the corresponding key was signaled as ready:
+ * our goal here is to call the is_key_ready() callback to see if the key
+ * is really able to serve the client, and in that case, unblock it. */
+void serveClientsBlockedOnKeyByModule(readyList *rl) {
+    dictEntry *de;
+
+    /* We serve clients in the same order they blocked for
+     * this key, from the first blocked to the last. */
+    de = dictFind(rl->db->blocking_keys,rl->key);
+    if (de) {
+        list *clients = dictGetVal(de);
+        int numclients = listLength(clients);
+
+        while(numclients--) {
+            listNode *clientnode = listFirst(clients);
+            client *receiver = clientnode->value;
+
+            if (!moduleIsKeyReady(receiver, rl->key)) continue;
+
+            moduleUnblockClient(receiver);
+        }
+    }
+}
+
 /* This function should be called by Redis every time a single command,
  * a MULTI/EXEC block, or a Lua script, terminated its execution after
  * being called by a client. It handles serving clients blocked in
@@ -480,6 +506,10 @@ void handleClientsBlockedOnKeys(void) {
                     serveClientsBlockedOnSortedSetKey(o,rl);
                 else if (o->type == OBJ_STREAM)
                     serveClientsBlockedOnStreamKey(o,rl);
+                /* We want to serve clients blocked on module keys
+                 * regardless of the object type: we don't know what the
+                 * module is trying to accomplish right now. */
+                serveClientsBlockedOnKeyByModule(rl);
             }
 
             /* Free this item. */
diff --git a/src/module.c b/src/module.c
index 113375e75..85bc9e808 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4060,6 +4060,24 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
     return bc;
 }
 
+/* This function is called from module.c in order to check if a module
+ * blocked for BLOCKED_MODULE and subtype 'on keys' (bc->blocked_on_keys true)
+ * can really be unblocked since the key is ready. */
+int moduleIsKeyReady(client *c, robj *key) {
+    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
+    RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
+    ctx.module = bc->module;
+    ctx.client = bc->client;
+    ctx.blocked_privdata = bc->privdata; /* In case the callback uses the
+                                            API to get the pointer to the
+                                            privdata, even if we provide it
+                                            as argument. */
+    selectDb(ctx.client, bc->dbid);
+    int ready = bc->is_key_ready(&ctx, key, bc->privdata);
+    moduleFreeContext(&ctx);
+    return ready;
+}
+
 /* Block a client in the context of a blocking command, returning an handle
  * which will be used, later, in order to unblock the client with a call to
  * RedisModule_UnblockClient(). The arguments specify callback functions
@@ -4137,6 +4155,25 @@ void RM_SignalKeyAsReady(RedisModuleCtx *ctx, RedisModuleString *key) {
     signalKeyAsReady(ctx->client->db, key);
 }
 
+/* Implements RM_UnblockClient() and moduleUnblockClient(). */
+int moduleUnblockClientByHandle(RedisModuleBlockedClient *bc, void *privdata) {
+    pthread_mutex_lock(&moduleUnblockedClientsMutex);
+    if (!bc->blocked_on_keys) bc->privdata = privdata;
+    listAddNodeTail(moduleUnblockedClients,bc);
+    if (write(server.module_blocked_pipe[1],"A",1) != 1) {
+        /* Ignore the error, this is best-effort. */
+    }
+    pthread_mutex_unlock(&moduleUnblockedClientsMutex);
+    return REDISMODULE_OK;
+}
+
+/* This API is used by the Redis core to unblock a client that was blocked
+ * by a module. */
+void moduleUnblockClient(client *c) {
+    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
+    moduleUnblockClientByHandle(bc,NULL);
+}
+
 /* Unblock a client blocked by `RedisModule_BlockedClient`. This will trigger
  * the reply callbacks to be called in order to reply to the client.
  * The 'privdata' argument will be accessible by the reply callback, so
@@ -4147,15 +4184,16 @@ void RM_SignalKeyAsReady(RedisModuleCtx *ctx, RedisModuleString *key) {
  * needs to be passed to the client, included but not limited some slow
  * to compute reply or some reply obtained via networking.
  *
- * Note: this function can be called from threads spawned by the module. */
+ * Note: this function can be called from threads spawned by the module.
+ *
+ * Note: when we unblock a client that is blocked for keys using
+ * the API RedisModule_BlockClientOnKeys(), the privdata argument here is
+ * not used, and the reply callback is called with the privdata pointer that
+ * was passed when blocking the client. Also note if you unblock clients
+ * blocked on keys in this way, the reply callback should be ready to handle
+ * the fact the key may not be ready at all. */
 int RM_UnblockClient(RedisModuleBlockedClient *bc, void *privdata) {
-    pthread_mutex_lock(&moduleUnblockedClientsMutex);
-    if (!bc->blocked_on_keys) bc->privdata = privdata;
-    listAddNodeTail(moduleUnblockedClients,bc);
-    if (write(server.module_blocked_pipe[1],"A",1) != 1) {
-        /* Ignore the error, this is best-effort. */
-    }
-    pthread_mutex_unlock(&moduleUnblockedClientsMutex);
+    moduleUnblockClientByHandle(bc,privdata);
     return REDISMODULE_OK;
 }
 
diff --git a/src/server.h b/src/server.h
index 97672d727..3a2bb1c7b 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1602,6 +1602,8 @@ ssize_t rdbSaveModulesAux(rio *rdb, int when);
 int moduleAllDatatypesHandleErrors();
 sds modulesCollectInfo(sds info, sds section, int for_crash_report, int sections);
 void moduleFireServerEvent(uint64_t eid, int subid, void *data);
+int moduleIsKeyReady(client *c, robj *key);
+void moduleUnblockClient(client *c);
 
 /* Utils */
 long long ustime(void);

From 228bc89ecbeeb61ee2a37ba7bd5f565cb5a78f63 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 10:30:54 +0100
Subject: [PATCH 05/15] Modules: block on keys: example on hellotype.c.

---
 src/modules/hellotype.c | 68 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/src/modules/hellotype.c b/src/modules/hellotype.c
index ba634c4a1..084408798 100644
--- a/src/modules/hellotype.c
+++ b/src/modules/hellotype.c
@@ -129,6 +129,7 @@ int HelloTypeInsert_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv,
 
     /* Insert the new element. */
     HelloTypeInsert(hto,value);
+    RedisModule_SignalKeyAsReady(ctx,argv[1]);
 
     RedisModule_ReplyWithLongLong(ctx,hto->len);
     RedisModule_ReplicateVerbatim(ctx);
@@ -190,6 +191,69 @@ int HelloTypeLen_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int
     return REDISMODULE_OK;
 }
 
+/* ====================== Example of a blocking command ==================== */
+
+/* Is_key_ready callback for blocking command HELLOTYPE.BRANGE */
+int HelloBlock_IsKeyReady(RedisModuleCtx *ctx, RedisModuleString *keyname, void *privdata) {
+    REDISMODULE_NOT_USED(privdata);
+
+    RedisModule_AutoMemory(ctx); /* Use automatic memory management. */
+    RedisModuleKey *key = RedisModule_OpenKey(ctx,keyname,REDISMODULE_READ);
+    int type = RedisModule_KeyType(key);
+    if (type != REDISMODULE_KEYTYPE_MODULE ||
+        RedisModule_ModuleTypeGetType(key) != HelloType)
+    {
+        return 0;
+    } else {
+        return 1;
+    }
+}
+
+/* Reply callback for blocking command HELLOTYPE.BRANGE */
+int HelloBlock_Reply(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+    return HelloTypeRange_RedisCommand(ctx,argv,argc-1);
+}
+
+/* Timeout callback for blocking command HELLOTYPE.BRANGE */
+int HelloBlock_Timeout(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+    return RedisModule_ReplyWithSimpleString(ctx,"Request timedout");
+}
+
+/* Private data freeing callback for HELLOTYPE.BRANGE command. */
+void HelloBlock_FreeData(RedisModuleCtx *ctx, void *privdata) {
+    REDISMODULE_NOT_USED(ctx);
+    RedisModule_Free(privdata);
+}
+
+/* HELLOTYPE.BRANGE key first count timeout -- This is a blocking verison of
+ * the RANGE operation, in order to show how to use the API
+ * RedisModule_BlockClientOnKeys(). */
+int HelloTypeBRange_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 5) return RedisModule_WrongArity(ctx);
+    RedisModule_AutoMemory(ctx); /* Use automatic memory management. */
+    RedisModuleKey *key = RedisModule_OpenKey(ctx,argv[1],
+        REDISMODULE_READ|REDISMODULE_WRITE);
+    int type = RedisModule_KeyType(key);
+    if (type != REDISMODULE_KEYTYPE_EMPTY &&
+        RedisModule_ModuleTypeGetType(key) != HelloType)
+    {
+        return RedisModule_ReplyWithError(ctx,REDISMODULE_ERRORMSG_WRONGTYPE);
+    }
+
+    long long timeout;
+    if (RedisModule_StringToLongLong(argv[4],&timeout) != REDISMODULE_OK) {
+        return RedisModule_ReplyWithError(ctx,
+            "ERR invalid timeout parameter");
+    }
+
+    void *privdata = RedisModule_Alloc(100);
+    RedisModule_BlockClientOnKeys(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout,argv+1,1,HelloBlock_IsKeyReady,privdata);
+    return REDISMODULE_OK;
+}
 
 /* ========================== "hellotype" type methods ======================= */
 
@@ -282,5 +346,9 @@ int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
         HelloTypeLen_RedisCommand,"readonly",1,1,1) == REDISMODULE_ERR)
         return REDISMODULE_ERR;
 
+    if (RedisModule_CreateCommand(ctx,"hellotype.brange",
+        HelloTypeBRange_RedisCommand,"readonly",1,1,1) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
     return REDISMODULE_OK;
 }

From 4534960b293d41fd5193c1d8a51a19453c2aabf6 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 10:32:59 +0100
Subject: [PATCH 06/15] Modules: remove spurious call from
 moduleHandleBlockedClients().

Now we handle propagation when we free the context.
---
 src/module.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/module.c b/src/module.c
index 85bc9e808..a11d3a306 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4262,7 +4262,6 @@ void moduleHandleBlockedClients(void) {
             ctx.client = bc->client;
             ctx.blocked_client = bc;
             bc->reply_callback(&ctx,(void**)c->argv,c->argc);
-            moduleHandlePropagationAfterCommandCallback(&ctx);
             moduleFreeContext(&ctx);
         }
 

From 91f4bdc9f9d80ba7431f093cb58b6c49f4021d0b Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 11:35:05 +0100
Subject: [PATCH 07/15] Modules: block on keys: use a better interface.

Using the is_key_ready() callback plus the reply callback later, creates
different issues AFAIK:

1. More complex API.
2. We need to call the reply callback() ASAP if the is_key_ready()
interface returned success, however the internals do not work in that
way, so when the reply callback is called the setup could be different.
To fix that, there is to break the current design that handles the
unblocked clients asyncrhonously, and run the list ASAP.
---
 src/blocked.c           |  3 +-
 src/module.c            | 74 +++++++++++++++++++++++++----------------
 src/modules/hellotype.c | 26 +++++++--------
 src/redismodule.h       |  4 ++-
 src/server.h            |  3 +-
 5 files changed, 65 insertions(+), 45 deletions(-)

diff --git a/src/blocked.c b/src/blocked.c
index 2b91c1b44..fb58f850b 100644
--- a/src/blocked.c
+++ b/src/blocked.c
@@ -174,6 +174,7 @@ void unblockClient(client *c) {
     } else if (c->btype == BLOCKED_WAIT) {
         unblockClientWaitingReplicas(c);
     } else if (c->btype == BLOCKED_MODULE) {
+        if (moduleClientIsBlockedOnKeys(c)) unblockClientWaitingData(c);
         unblockClientFromModule(c);
     } else {
         serverPanic("Unknown btype in unblockClient().");
@@ -449,7 +450,7 @@ void serveClientsBlockedOnKeyByModule(readyList *rl) {
             listNode *clientnode = listFirst(clients);
             client *receiver = clientnode->value;
 
-            if (!moduleIsKeyReady(receiver, rl->key)) continue;
+            if (!moduleTryServeClientBlockedOnKey(receiver, rl->key)) continue;
 
             moduleUnblockClient(receiver);
         }
diff --git a/src/module.c b/src/module.c
index a11d3a306..8837ae017 100644
--- a/src/module.c
+++ b/src/module.c
@@ -140,6 +140,9 @@ struct RedisModuleCtx {
     void **postponed_arrays;        /* To set with RM_ReplySetArrayLength(). */
     int postponed_arrays_count;     /* Number of entries in postponed_arrays. */
     void *blocked_privdata;         /* Privdata set when unblocking a client. */
+    RedisModuleString *blocked_ready_key; /* Key ready when the reply callback
+                                             gets called for clients blocked
+                                             on keys. */
 
     /* Used if there is the REDISMODULE_CTX_KEYS_POS_REQUEST flag set. */
     int *keys_pos;
@@ -153,7 +156,7 @@ struct RedisModuleCtx {
 };
 typedef struct RedisModuleCtx RedisModuleCtx;
 
-#define REDISMODULE_CTX_INIT {(void*)(unsigned long)&RM_GetApi, NULL, NULL, NULL, NULL, 0, 0, 0, NULL, 0, NULL, NULL, 0, NULL, {0}}
+#define REDISMODULE_CTX_INIT {(void*)(unsigned long)&RM_GetApi, NULL, NULL, NULL, NULL, 0, 0, 0, NULL, 0, NULL, NULL, NULL, 0, NULL, {0}}
 #define REDISMODULE_CTX_MULTI_EMITTED (1<<0)
 #define REDISMODULE_CTX_AUTO_MEMORY (1<<1)
 #define REDISMODULE_CTX_KEYS_POS_REQUEST (1<<2)
@@ -246,14 +249,6 @@ typedef struct RedisModuleBlockedClient {
                                        in thread safe contexts. */
     int dbid;           /* Database number selected by the original client. */
     int blocked_on_keys;    /* If blocked via RM_BlockClientOnKeys(). */
-    int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *keyname,
-                        void *privdata);  /* When blocking on keys, even if the
-                                             key is signaled as ready, maybe it
-                                             was modified afterward before the
-                                             client unblocks. So we always
-                                             need a callback that tells us if
-                                             the key is ready in order to serve
-                                             the next blocked client. */
 } RedisModuleBlockedClient;
 
 static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
@@ -4002,10 +3997,10 @@ void unblockClientFromModule(client *c) {
  * RM_BlockClient() and RM_BlockClientOnKeys() depending on the fact the
  * keys are passed or not.
  *
- * When not blocking for keys, the keys, numkeys, is_key_ready callback
- * and privdata parameters are not needed. The privdata in that case must
- * be NULL, since later is RM_UnblockClient() that will provide some private
- * data that the reply callback will receive.
+ * When not blocking for keys, the keys, numkeys, and privdata parameters are
+ * not needed. The privdata in that case must be NULL, since later is
+ * RM_UnblockClient() that will provide some private data that the reply
+ * callback will receive.
  *
  * Instead when blocking for keys, normally RM_UnblockClient() will not be
  * called (because the client will unblock when the key is modified), so
@@ -4017,7 +4012,7 @@ void unblockClientFromModule(client *c) {
  * in that case the privdata argument is disregarded, because we pass the
  * reply callback the privdata that is set here while blocking.
  */
-RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *key, void *privdata), void *privdata) {
+RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata) {
     client *c = ctx->client;
     int islua = c->flags & CLIENT_LUA;
     int ismulti = c->flags & CLIENT_MULTI;
@@ -4041,7 +4036,6 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
     bc->reply_client = createClient(NULL);
     bc->reply_client->flags |= CLIENT_MODULE;
     bc->dbid = c->db->id;
-    bc->is_key_ready = is_key_ready;
     bc->blocked_on_keys = keys != NULL;
     c->bpop.timeout = timeout;
 
@@ -4062,20 +4056,24 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
 
 /* This function is called from module.c in order to check if a module
  * blocked for BLOCKED_MODULE and subtype 'on keys' (bc->blocked_on_keys true)
- * can really be unblocked since the key is ready. */
-int moduleIsKeyReady(client *c, robj *key) {
+ * can really be unblocked, since the module was able to serve the client.
+ * If the callback returns REDISMODULE_OK, then the client can be unblocked,
+ * otherwise the client remains blocked and we'll retry again when one of
+ * the keys it blocked for becomes "ready" again. */
+int moduleTryServeClientBlockedOnKey(client *c, robj *key) {
+    int served = 0;
     RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
     RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
+    ctx.flags |= REDISMODULE_CTX_BLOCKED_REPLY;
+    ctx.blocked_ready_key = key;
+    ctx.blocked_privdata = bc->privdata;
     ctx.module = bc->module;
     ctx.client = bc->client;
-    ctx.blocked_privdata = bc->privdata; /* In case the callback uses the
-                                            API to get the pointer to the
-                                            privdata, even if we provide it
-                                            as argument. */
-    selectDb(ctx.client, bc->dbid);
-    int ready = bc->is_key_ready(&ctx, key, bc->privdata);
+    ctx.blocked_client = bc;
+    if (bc->reply_callback(&ctx,(void**)c->argv,c->argc) == REDISMODULE_OK)
+        served = 1;
     moduleFreeContext(&ctx);
-    return ready;
+    return served;
 }
 
 /* Block a client in the context of a blocking command, returning an handle
@@ -4095,7 +4093,7 @@ int moduleIsKeyReady(client *c, robj *key) {
  *                      by RedisModule_UnblockClient() call.
  */
 RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms) {
-    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, NULL,0,NULL,NULL);
+    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, NULL,0,NULL);
 }
 
 /* This call is similar to RedisModule_BlockClient(), however in this case we
@@ -4142,8 +4140,8 @@ RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc
  * information about the specific unblocking operation that you are
  * implementing. Such information will be freed using the free_privdata
  * callback provided by the user. */
-RedisModuleBlockedClient *RM_BlockClientOnKeys(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *keyname, void *privdata), void *privdata) {
-    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,is_key_ready,privdata);
+RedisModuleBlockedClient *RM_BlockClientOnKeys(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata) {
+    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,privdata);
 }
 
 /* This function is used in order to potentially unblock a client blocked
@@ -4174,6 +4172,13 @@ void moduleUnblockClient(client *c) {
     moduleUnblockClientByHandle(bc,NULL);
 }
 
+/* Return true if the client 'c' was blocked by a module using
+ * RM_BlockClientOnKeys(). */
+int moduleClientIsBlockedOnKeys(client *c) {
+    RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
+    return bc->blocked_on_keys;
+}
+
 /* Unblock a client blocked by `RedisModule_BlockedClient`. This will trigger
  * the reply callbacks to be called in order to reply to the client.
  * The 'privdata' argument will be accessible by the reply callback, so
@@ -4253,11 +4258,15 @@ void moduleHandleBlockedClients(void) {
          * touch the shared list. */
 
         /* Call the reply callback if the client is valid and we have
-         * any callback. */
-        if (c && bc->reply_callback) {
+         * any callback. However the callback is not called if the client
+         * was blocked on keys (RM_BlockClientOnKeys()), because we already
+         * called such callback in moduleTryServeClientBlockedOnKey() when
+         * the key was signaled as ready. */
+        if (c && !bc->blocked_on_keys && bc->reply_callback) {
             RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
             ctx.flags |= REDISMODULE_CTX_BLOCKED_REPLY;
             ctx.blocked_privdata = bc->privdata;
+            ctx.blocked_ready_key = NULL;
             ctx.module = bc->module;
             ctx.client = bc->client;
             ctx.blocked_client = bc;
@@ -4349,6 +4358,12 @@ void *RM_GetBlockedClientPrivateData(RedisModuleCtx *ctx) {
     return ctx->blocked_privdata;
 }
 
+/* Get the key that is ready when the reply callback is called in the context
+ * of a client blocked by RedisModule_BlockClientOnKeys(). */
+RedisModuleString *RM_GetBlockedClientReadyKey(RedisModuleCtx *ctx) {
+    return ctx->blocked_ready_key;
+}
+
 /* Get the blocked client associated with a given context.
  * This is useful in the reply and timeout callbacks of blocked clients,
  * before sometimes the module has the blocked client handle references
@@ -6682,4 +6697,5 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(SubscribeToServerEvent);
     REGISTER_API(BlockClientOnKeys);
     REGISTER_API(SignalKeyAsReady);
+    REGISTER_API(GetBlockedClientReadyKey);
 }
diff --git a/src/modules/hellotype.c b/src/modules/hellotype.c
index 084408798..dafbadbe5 100644
--- a/src/modules/hellotype.c
+++ b/src/modules/hellotype.c
@@ -193,26 +193,26 @@ int HelloTypeLen_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int
 
 /* ====================== Example of a blocking command ==================== */
 
-/* Is_key_ready callback for blocking command HELLOTYPE.BRANGE */
-int HelloBlock_IsKeyReady(RedisModuleCtx *ctx, RedisModuleString *keyname, void *privdata) {
-    REDISMODULE_NOT_USED(privdata);
+/* Reply callback for blocking command HELLOTYPE.BRANGE, this will get
+ * called when the key we blocked for is ready: we need to check if we
+ * can really serve the client, and reply OK or ERR accordingly. */
+int HelloBlock_Reply(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
 
-    RedisModule_AutoMemory(ctx); /* Use automatic memory management. */
+    RedisModuleString *keyname = RedisModule_GetBlockedClientReadyKey(ctx);
     RedisModuleKey *key = RedisModule_OpenKey(ctx,keyname,REDISMODULE_READ);
     int type = RedisModule_KeyType(key);
     if (type != REDISMODULE_KEYTYPE_MODULE ||
         RedisModule_ModuleTypeGetType(key) != HelloType)
     {
-        return 0;
-    } else {
-        return 1;
+        RedisModule_CloseKey(key);
+        return REDISMODULE_ERR;
     }
-}
 
-/* Reply callback for blocking command HELLOTYPE.BRANGE */
-int HelloBlock_Reply(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
-    REDISMODULE_NOT_USED(argv);
-    REDISMODULE_NOT_USED(argc);
+    /* In case the key is able to serve our blocked client, let's directly
+     * use our original command implementation to make this example simpler. */
+    RedisModule_CloseKey(key);
     return HelloTypeRange_RedisCommand(ctx,argv,argc-1);
 }
 
@@ -251,7 +251,7 @@ int HelloTypeBRange_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv,
     }
 
     void *privdata = RedisModule_Alloc(100);
-    RedisModule_BlockClientOnKeys(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout,argv+1,1,HelloBlock_IsKeyReady,privdata);
+    RedisModule_BlockClientOnKeys(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout,argv+1,1,privdata);
     return REDISMODULE_OK;
 }
 
diff --git a/src/redismodule.h b/src/redismodule.h
index 5b4c31b19..1b284770b 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -492,8 +492,9 @@ int REDISMODULE_API_FUNC(RedisModule_InfoAddFieldDouble)(RedisModuleInfoCtx *ctx
 int REDISMODULE_API_FUNC(RedisModule_InfoAddFieldLongLong)(RedisModuleInfoCtx *ctx, char *field, long long value);
 int REDISMODULE_API_FUNC(RedisModule_InfoAddFieldULongLong)(RedisModuleInfoCtx *ctx, char *field, unsigned long long value);
 int REDISMODULE_API_FUNC(RedisModule_SubscribeToServerEvent)(RedisModuleCtx *ctx, RedisModuleEvent event, RedisModuleEventCallback callback);
-RedisModuleBlockedClient *REDISMODULE_API_FUNC(RedisModule_BlockClientOnKeys)(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, int (*is_key_ready)(RedisModuleCtx*, RedisModuleString *keyname, void *privdata), void *privdata);
+RedisModuleBlockedClient *REDISMODULE_API_FUNC(RedisModule_BlockClientOnKeys)(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata);
 void REDISMODULE_API_FUNC(RedisModule_SignalKeyAsReady)(RedisModuleCtx *ctx, RedisModuleString *key);
+RedisModuleString *REDISMODULE_API_FUNC(RedisModule_GetBlockedClientReadyKey)(RedisModuleCtx *ctx);
 
 /* Experimental APIs */
 #ifdef REDISMODULE_EXPERIMENTAL_API
@@ -692,6 +693,7 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(SubscribeToServerEvent);
     REDISMODULE_GET_API(BlockClientOnKeys);
     REDISMODULE_GET_API(SignalKeyAsReady);
+    REDISMODULE_GET_API(GetBlockedClientReadyKey);
 
 #ifdef REDISMODULE_EXPERIMENTAL_API
     REDISMODULE_GET_API(GetThreadSafeContext);
diff --git a/src/server.h b/src/server.h
index 3a2bb1c7b..f724f7d64 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1602,8 +1602,9 @@ ssize_t rdbSaveModulesAux(rio *rdb, int when);
 int moduleAllDatatypesHandleErrors();
 sds modulesCollectInfo(sds info, sds section, int for_crash_report, int sections);
 void moduleFireServerEvent(uint64_t eid, int subid, void *data);
-int moduleIsKeyReady(client *c, robj *key);
+int moduleTryServeClientBlockedOnKey(client *c, robj *key);
 void moduleUnblockClient(client *c);
+int moduleClientIsBlockedOnKeys(client *c);
 
 /* Utils */
 long long ustime(void);

From 629081f839498734d3426d71653619d4f9e93dc9 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 11:43:45 +0100
Subject: [PATCH 08/15] Modules: block on keys: fix the top comments.

---
 src/module.c | 41 +++++++++++++++++++++++------------------
 1 file changed, 23 insertions(+), 18 deletions(-)

diff --git a/src/module.c b/src/module.c
index 8837ae017..353b6f426 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4119,36 +4119,41 @@ RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc
  * Anyway we can't be sure if the client should be unblocked just because the
  * key is signaled as ready: for instance a successive operation may change the
  * key, or a client in queue before this one can be served, modifying the key
- * as well and making it empty again. So when blocking for keys, we need to
- * register a callback called is_key_ready. This callback gets called with
- * a context, selected with the right database, and the key name: if it
- * returns 1, then we proceed calling the reply callback, otherwise if the
- * is_key_ready callback returns 0 the client is not unblocked, since the
- * key is yet not ready.
+ * as well and making it empty again. So when a client is blocked with
+ * RedisModule_BlockClientOnKeys() the reply callback is not called after
+ * RM_UnblockCLient() is called, but every time a key is signaled as ready:
+ * if the reply callback can serve the client, it returns REDISMODULE_OK
+ * and the client is unblocked, otherwise it will return REDISMODULE_ERR
+ * and we'll try again later.
+ *
+ * The reply callback can access the key that was signaled as ready by
+ * calling the API RedisModule_GetBlockedClientReadyKey(), that returns
+ * just the string name of the key as a RedisModuleString object.
  *
  * Thanks to this system we can setup complex blocking scenarios, like
  * unblocking a client only if a list contains at least 5 items or other
  * more fancy logics.
  *
  * Note that another difference with RedisModule_BlockClient(), is that here
- * we pass the private data directly when blocking the client: such private
- * data will be later provided both to the is_key_ready callback, and to the
- * reply callback. Normally in RedisModule_BlockClient() the private data
- * to reply to the client is passed when calling RedisModule_UnblockClient()
- * but here the unblocking is performed by Redis itself, so we need to have
- * some private data before hand. The private data is used to store any
- * information about the specific unblocking operation that you are
- * implementing. Such information will be freed using the free_privdata
- * callback provided by the user. */
+ * we pass the private data directly when blocking the client: it will
+ * be accessible later in the reply callback. Normally when blocking with
+ * RedisModule_BlockClient() the private data to reply to the client is
+ * passed when calling RedisModule_UnblockClient() but here the unblocking
+ * is performed by Redis itself, so we need to have some private data before
+ * hand. The private data is used to store any information about the specific
+ * unblocking operation that you are implementing. Such information will be
+ * freed using the free_privdata callback provided by the user.
+ *
+ * However the reply callback will be able to access the argument vector of
+ * the command, so the private data is often not needed. */
 RedisModuleBlockedClient *RM_BlockClientOnKeys(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback, RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*), long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata) {
     return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,privdata);
 }
 
 /* This function is used in order to potentially unblock a client blocked
  * on keys with RedisModule_BlockClientOnKeys(). When this function is called,
- * all the clients blocked for this key will get their is_key_ready callback,
- * and if the callback returns non-zero the client will be unblocked and the
- * reply callback will be called in order to reply to the client. */
+ * all the clients blocked for this key will get their reply callback called,
+ * and if the callback returns REDISMODULE_OK the client will be unblocked. */
 void RM_SignalKeyAsReady(RedisModuleCtx *ctx, RedisModuleString *key) {
     signalKeyAsReady(ctx->client->db, key);
 }

From 66f55bc5c15d72542983f37c6c1b48b0c1618917 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 12:23:55 +0100
Subject: [PATCH 09/15] Modules: block on keys: fix bugs in processing order.

---
 src/blocked.c | 16 ++++++++++++++++
 src/module.c  |  7 +++++++
 2 files changed, 23 insertions(+)

diff --git a/src/blocked.c b/src/blocked.c
index fb58f850b..3110c00fc 100644
--- a/src/blocked.c
+++ b/src/blocked.c
@@ -450,6 +450,22 @@ void serveClientsBlockedOnKeyByModule(readyList *rl) {
             listNode *clientnode = listFirst(clients);
             client *receiver = clientnode->value;
 
+            /* Put at the tail, so that at the next call
+             * we'll not run into it again: clients here may not be
+             * ready to be served, so they'll remain in the list
+             * sometimes. We want also be able to skip clients that are
+             * not blocked for the MODULE type safely. */
+            listDelNode(clients,clientnode);
+            listAddNodeTail(clients,receiver);
+
+            if (receiver->btype != BLOCKED_MODULE) continue;
+
+            /* Note that if *this* client cannot be served by this key,
+             * it does not mean that another client that is next into the
+             * list cannot be served as well: they may be blocked by
+             * different modules with different triggers to consider if a key
+             * is ready or not. This means we can't exit the loop but need
+             * to continue after the first failure. */
             if (!moduleTryServeClientBlockedOnKey(receiver, rl->key)) continue;
 
             moduleUnblockClient(receiver);
diff --git a/src/module.c b/src/module.c
index 353b6f426..248a55e62 100644
--- a/src/module.c
+++ b/src/module.c
@@ -249,6 +249,7 @@ typedef struct RedisModuleBlockedClient {
                                        in thread safe contexts. */
     int dbid;           /* Database number selected by the original client. */
     int blocked_on_keys;    /* If blocked via RM_BlockClientOnKeys(). */
+    int unblocked;          /* Already on the moduleUnblocked list. */
 } RedisModuleBlockedClient;
 
 static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
@@ -4037,6 +4038,7 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
     bc->reply_client->flags |= CLIENT_MODULE;
     bc->dbid = c->db->id;
     bc->blocked_on_keys = keys != NULL;
+    bc->unblocked = 0;
     c->bpop.timeout = timeout;
 
     if (islua || ismulti) {
@@ -4063,6 +4065,10 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
 int moduleTryServeClientBlockedOnKey(client *c, robj *key) {
     int served = 0;
     RedisModuleBlockedClient *bc = c->bpop.module_blocked_handle;
+    /* Protect against re-processing: don't serve clients that are already
+     * in the unblocking list for any reason (including RM_UnblockClient()
+     * explicit call). */
+    if (bc->unblocked) return REDISMODULE_ERR;
     RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
     ctx.flags |= REDISMODULE_CTX_BLOCKED_REPLY;
     ctx.blocked_ready_key = key;
@@ -4162,6 +4168,7 @@ void RM_SignalKeyAsReady(RedisModuleCtx *ctx, RedisModuleString *key) {
 int moduleUnblockClientByHandle(RedisModuleBlockedClient *bc, void *privdata) {
     pthread_mutex_lock(&moduleUnblockedClientsMutex);
     if (!bc->blocked_on_keys) bc->privdata = privdata;
+    bc->unblocked = 1;
     listAddNodeTail(moduleUnblockedClients,bc);
     if (write(server.module_blocked_pipe[1],"A",1) != 1) {
         /* Ignore the error, this is best-effort. */

From 37bf3e18cbc4db5538940ac4a6006627122e1c17 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 12:31:22 +0100
Subject: [PATCH 10/15] Modules: block ok keys: improve example.

---
 src/modules/hellotype.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/modules/hellotype.c b/src/modules/hellotype.c
index dafbadbe5..4f2d1d730 100644
--- a/src/modules/hellotype.c
+++ b/src/modules/hellotype.c
@@ -244,12 +244,20 @@ int HelloTypeBRange_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv,
         return RedisModule_ReplyWithError(ctx,REDISMODULE_ERRORMSG_WRONGTYPE);
     }
 
+    /* Parse the timeout before even trying to serve the client synchronously,
+     * so that we always fail ASAP on syntax errors. */
     long long timeout;
     if (RedisModule_StringToLongLong(argv[4],&timeout) != REDISMODULE_OK) {
         return RedisModule_ReplyWithError(ctx,
             "ERR invalid timeout parameter");
     }
 
+    /* Can we serve the reply synchronously? */
+    if (type != REDISMODULE_KEYTYPE_EMPTY) {
+        return HelloTypeRange_RedisCommand(ctx,argv,argc-1);
+    }
+
+    /* Otherwise let's block on the key. */
     void *privdata = RedisModule_Alloc(100);
     RedisModule_BlockClientOnKeys(ctx,HelloBlock_Reply,HelloBlock_Timeout,HelloBlock_FreeData,timeout,argv+1,1,privdata);
     return REDISMODULE_OK;

From 825adcf3f5775271583ebe4df0ba92fd8f9c821b Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 17:38:58 +0100
Subject: [PATCH 11/15] Modules: block on keys: finish implementing
 RM_UnblockClient().

---
 src/module.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/module.c b/src/module.c
index 248a55e62..a4384163a 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4201,15 +4201,24 @@ int moduleClientIsBlockedOnKeys(client *c) {
  * needs to be passed to the client, included but not limited some slow
  * to compute reply or some reply obtained via networking.
  *
- * Note: this function can be called from threads spawned by the module.
+ * Note 1: this function can be called from threads spawned by the module.
  *
- * Note: when we unblock a client that is blocked for keys using
+ * Note 2: when we unblock a client that is blocked for keys using
  * the API RedisModule_BlockClientOnKeys(), the privdata argument here is
  * not used, and the reply callback is called with the privdata pointer that
- * was passed when blocking the client. Also note if you unblock clients
- * blocked on keys in this way, the reply callback should be ready to handle
- * the fact the key may not be ready at all. */
+ * was passed when blocking the client.
+ *
+ * Unblocking a client that was blocked for keys using this API will still
+ * require the client to get some reply, so the function will use the
+ * "timeout" handler in order to do so. */
 int RM_UnblockClient(RedisModuleBlockedClient *bc, void *privdata) {
+    if (bc->blocked_on_keys) {
+        /* In theory the user should always pass the timeout handler as an
+         * argument, but better to be safe than sorry. */
+        if (bc->timeout_callback == NULL) return REDISMODULE_ERR;
+        if (bc->unblocked) return REDISMODULE_OK;
+        if (bc->client) moduleBlockedClientTimedOut(bc->client);
+    }
     moduleUnblockClientByHandle(bc,privdata);
     return REDISMODULE_OK;
 }

From dd5feec5e81288950784740ad23d9dc13b7df9a2 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 17:45:07 +0100
Subject: [PATCH 12/15] Modules: block on keys: fix stale comment.

---
 src/blocked.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/blocked.c b/src/blocked.c
index 3110c00fc..14c2ff830 100644
--- a/src/blocked.c
+++ b/src/blocked.c
@@ -434,8 +434,9 @@ void serveClientsBlockedOnStreamKey(robj *o, readyList *rl) {
 /* Helper function for handleClientsBlockedOnKeys(). This function is called
  * in order to check if we can serve clients blocked by modules using
  * RM_BlockClientOnKeys(), when the corresponding key was signaled as ready:
- * our goal here is to call the is_key_ready() callback to see if the key
- * is really able to serve the client, and in that case, unblock it. */
+ * our goal here is to call the RedisModuleBlockedClient reply() callback to
+ * see if the key is really able to serve the client, and in that case,
+ * unblock it. */
 void serveClientsBlockedOnKeyByModule(readyList *rl) {
     dictEntry *de;
 

From fdaea2a7a7eed1499f46bb98552f8d8bb8dc7e9d Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Thu, 31 Oct 2019 18:07:33 +0100
Subject: [PATCH 13/15] Modules: fix thread safe context creation crash.

See #6525, this likely creates a NULL deference if the client was
terminated by Redis between the creation of the blocked client and the
creation of the thread safe context.
---
 src/module.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/module.c b/src/module.c
index f298ec760..f9f654b42 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4463,7 +4463,7 @@ RedisModuleCtx *RM_GetThreadSafeContext(RedisModuleBlockedClient *bc) {
     ctx->client = createClient(NULL);
     if (bc) {
         selectDb(ctx->client,bc->dbid);
-        ctx->client->id = bc->client->id;
+        if (bc->client) ctx->client->id = bc->client->id;
     }
     return ctx;
 }

From 87332ce524e30d4949d2144a4da15b5ae17e5051 Mon Sep 17 00:00:00 2001
From: Oran Agra <oran@redislabs.com>
Date: Sun, 3 Nov 2019 17:35:35 +0200
Subject: [PATCH 14/15] Module API for PUBLISH, FLUSHALL, RANDOMKEY, DBSIZE

---
 src/db.c          | 44 ++++++++++++++++++++++++--------------------
 src/module.c      | 35 +++++++++++++++++++++++++++++++++++
 src/redismodule.h |  8 ++++++++
 src/server.h      |  2 ++
 4 files changed, 69 insertions(+), 20 deletions(-)

diff --git a/src/db.c b/src/db.c
index 2c0a0cdd3..ad19b42dd 100644
--- a/src/db.c
+++ b/src/db.c
@@ -461,6 +461,29 @@ int getFlushCommandFlags(client *c, int *flags) {
     return C_OK;
 }
 
+/* Flushes the whole server data set. */
+void flushAllDataAndResetRDB(int flags) {
+    server.dirty += emptyDb(-1,flags,NULL);
+    if (server.rdb_child_pid != -1) killRDBChild();
+    if (server.saveparamslen > 0) {
+        /* Normally rdbSave() will reset dirty, but we don't want this here
+         * as otherwise FLUSHALL will not be replicated nor put into the AOF. */
+        int saved_dirty = server.dirty;
+        rdbSaveInfo rsi, *rsiptr;
+        rsiptr = rdbPopulateSaveInfo(&rsi);
+        rdbSave(server.rdb_filename,rsiptr);
+        server.dirty = saved_dirty;
+    }
+    server.dirty++;
+#if defined(USE_JEMALLOC)
+    /* jemalloc 5 doesn't release pages back to the OS when there's no traffic.
+     * for large databases, flushdb blocks for long anyway, so a bit more won't
+     * harm and this way the flush and purge will be synchroneus. */
+    if (!(flags & EMPTYDB_ASYNC))
+        jemalloc_purge();
+#endif
+}
+
 /* FLUSHDB [ASYNC]
  *
  * Flushes the currently SELECTed Redis DB. */
@@ -484,28 +507,9 @@ void flushdbCommand(client *c) {
  * Flushes the whole server data set. */
 void flushallCommand(client *c) {
     int flags;
-
     if (getFlushCommandFlags(c,&flags) == C_ERR) return;
-    server.dirty += emptyDb(-1,flags,NULL);
+    flushAllDataAndResetRDB(flags);
     addReply(c,shared.ok);
-    if (server.rdb_child_pid != -1) killRDBChild();
-    if (server.saveparamslen > 0) {
-        /* Normally rdbSave() will reset dirty, but we don't want this here
-         * as otherwise FLUSHALL will not be replicated nor put into the AOF. */
-        int saved_dirty = server.dirty;
-        rdbSaveInfo rsi, *rsiptr;
-        rsiptr = rdbPopulateSaveInfo(&rsi);
-        rdbSave(server.rdb_filename,rsiptr);
-        server.dirty = saved_dirty;
-    }
-    server.dirty++;
-#if defined(USE_JEMALLOC)
-    /* jemalloc 5 doesn't release pages back to the OS when there's no traffic.
-     * for large databases, flushdb blocks for long anyway, so a bit more won't
-     * harm and this way the flush and purge will be synchroneus. */
-    if (!(flags & EMPTYDB_ASYNC))
-        jemalloc_purge();
-#endif
 }
 
 /* This command implements DEL and LAZYDEL. */
diff --git a/src/module.c b/src/module.c
index f9f654b42..5453aed47 100644
--- a/src/module.c
+++ b/src/module.c
@@ -1677,6 +1677,15 @@ int RM_GetClientInfoById(void *ci, uint64_t id) {
     return modulePopulateClientInfoStructure(ci,client,structver);
 }
 
+/* Publish a message to subscribers (see PUBLISH command). */
+int RM_PublishMessage(RedisModuleCtx *ctx, RedisModuleString *channel, RedisModuleString *message) {
+    UNUSED(ctx);
+    int receivers = pubsubPublishMessage(channel, message);
+    if (server.cluster_enabled)
+        clusterPropagatePublish(channel, message);
+    return receivers;
+}
+
 /* Return the currently selected DB. */
 int RM_GetSelectedDb(RedisModuleCtx *ctx) {
     return ctx->client->db->id;
@@ -1964,6 +1973,28 @@ int RM_SetExpire(RedisModuleKey *key, mstime_t expire) {
     return REDISMODULE_OK;
 }
 
+/* Performs similar operation to FLUSHALL, and optionally start a new AOF file (if enabled)
+ * If restart_aof is true, you must make sure the command that triggered this call is not
+ * propagated to the AOF file.
+ * When async is set to true, db contents will be freed by a background thread. */
+void RM_ResetDataset(int restart_aof, int async) {
+    if (restart_aof && server.aof_state != AOF_OFF) stopAppendOnly();
+    flushAllDataAndResetRDB(async? EMPTYDB_ASYNC: EMPTYDB_NO_FLAGS);
+    if (server.aof_enabled && restart_aof) restartAOFAfterSYNC();
+}
+
+/* Returns the number of keys in the current db. */
+unsigned long long RM_DbSize(RedisModuleCtx *ctx) {
+    return dictSize(ctx->client->db->dict);
+}
+
+/* Returns a name of a random key, or NULL if current db is empty. */
+RedisModuleString *RM_RandomKey(RedisModuleCtx *ctx) {
+    robj *key = dbRandomKey(ctx->client->db);
+    autoMemoryAdd(ctx,REDISMODULE_AM_STRING,key);
+    return key;
+}
+
 /* --------------------------------------------------------------------------
  * Key API for String type
  * -------------------------------------------------------------------------- */
@@ -6630,6 +6661,9 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(StringTruncate);
     REGISTER_API(SetExpire);
     REGISTER_API(GetExpire);
+    REGISTER_API(ResetDataset);
+    REGISTER_API(DbSize);
+    REGISTER_API(RandomKey);
     REGISTER_API(ZsetAdd);
     REGISTER_API(ZsetIncrby);
     REGISTER_API(ZsetScore);
@@ -6757,6 +6791,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(InfoAddFieldLongLong);
     REGISTER_API(InfoAddFieldULongLong);
     REGISTER_API(GetClientInfoById);
+    REGISTER_API(PublishMessage);
     REGISTER_API(SubscribeToServerEvent);
     REGISTER_API(BlockClientOnKeys);
     REGISTER_API(SignalKeyAsReady);
diff --git a/src/redismodule.h b/src/redismodule.h
index ea0d6a139..77019f89e 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -416,6 +416,9 @@ char *REDISMODULE_API_FUNC(RedisModule_StringDMA)(RedisModuleKey *key, size_t *l
 int REDISMODULE_API_FUNC(RedisModule_StringTruncate)(RedisModuleKey *key, size_t newlen);
 mstime_t REDISMODULE_API_FUNC(RedisModule_GetExpire)(RedisModuleKey *key);
 int REDISMODULE_API_FUNC(RedisModule_SetExpire)(RedisModuleKey *key, mstime_t expire);
+void REDISMODULE_API_FUNC(RedisModule_ResetDataset)(int restart_aof, int async);
+unsigned long long REDISMODULE_API_FUNC(RedisModule_DbSize)(RedisModuleCtx *ctx);
+RedisModuleString *REDISMODULE_API_FUNC(RedisModule_RandomKey)(RedisModuleCtx *ctx);
 int REDISMODULE_API_FUNC(RedisModule_ZsetAdd)(RedisModuleKey *key, double score, RedisModuleString *ele, int *flagsptr);
 int REDISMODULE_API_FUNC(RedisModule_ZsetIncrby)(RedisModuleKey *key, double score, RedisModuleString *ele, int *flagsptr, double *newscore);
 int REDISMODULE_API_FUNC(RedisModule_ZsetScore)(RedisModuleKey *key, RedisModuleString *ele, double *score);
@@ -435,6 +438,7 @@ int REDISMODULE_API_FUNC(RedisModule_IsKeysPositionRequest)(RedisModuleCtx *ctx)
 void REDISMODULE_API_FUNC(RedisModule_KeyAtPos)(RedisModuleCtx *ctx, int pos);
 unsigned long long REDISMODULE_API_FUNC(RedisModule_GetClientId)(RedisModuleCtx *ctx);
 int REDISMODULE_API_FUNC(RedisModule_GetClientInfoById)(void *ci, uint64_t id);
+int REDISMODULE_API_FUNC(RedisModule_PublishMessage)(RedisModuleCtx *ctx, RedisModuleString *channel, RedisModuleString *message);
 int REDISMODULE_API_FUNC(RedisModule_GetContextFlags)(RedisModuleCtx *ctx);
 void *REDISMODULE_API_FUNC(RedisModule_PoolAlloc)(RedisModuleCtx *ctx, size_t bytes);
 RedisModuleType *REDISMODULE_API_FUNC(RedisModule_CreateDataType)(RedisModuleCtx *ctx, const char *name, int encver, RedisModuleTypeMethods *typemethods);
@@ -619,6 +623,9 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(StringTruncate);
     REDISMODULE_GET_API(GetExpire);
     REDISMODULE_GET_API(SetExpire);
+    REDISMODULE_GET_API(ResetDataset);
+    REDISMODULE_GET_API(DbSize);
+    REDISMODULE_GET_API(RandomKey);
     REDISMODULE_GET_API(ZsetAdd);
     REDISMODULE_GET_API(ZsetIncrby);
     REDISMODULE_GET_API(ZsetScore);
@@ -705,6 +712,7 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(InfoAddFieldLongLong);
     REDISMODULE_GET_API(InfoAddFieldULongLong);
     REDISMODULE_GET_API(GetClientInfoById);
+    REDISMODULE_GET_API(PublishMessage);
     REDISMODULE_GET_API(SubscribeToServerEvent);
     REDISMODULE_GET_API(BlockClientOnKeys);
     REDISMODULE_GET_API(SignalKeyAsReady);
diff --git a/src/server.h b/src/server.h
index f724f7d64..4287d1adf 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1862,6 +1862,7 @@ void aofRewriteBufferReset(void);
 unsigned long aofRewriteBufferSize(void);
 ssize_t aofReadDiffFromParent(void);
 void killAppendOnlyChild(void);
+void restartAOFAfterSYNC();
 
 /* Child info */
 void openChildInfoPipe(void);
@@ -2101,6 +2102,7 @@ robj *dbUnshareStringValue(redisDb *db, robj *key, robj *o);
 #define EMPTYDB_ASYNC (1<<0)    /* Reclaim memory in another thread. */
 long long emptyDb(int dbnum, int flags, void(callback)(void*));
 long long emptyDbGeneric(redisDb *dbarray, int dbnum, int flags, void(callback)(void*));
+void flushAllDataAndResetRDB(int flags);
 long long dbTotalServerKeyCount();
 
 int selectDb(client *c, int id);

From b81f486c2f0d9f8ae14fc7c0568ba59e629995d6 Mon Sep 17 00:00:00 2001
From: Guy Benoish <guy.benoish@redislabs.com>
Date: Thu, 29 Mar 2018 17:46:13 +0700
Subject: [PATCH 15/15] Modules: Test RedisModule_BlockClientOnKeys

---
 runtest-moduleapi                    |   1 +
 tests/modules/Makefile               |   3 +-
 tests/modules/blockonkeys.c          | 261 +++++++++++++++++++++++++++
 tests/unit/moduleapi/blockonkeys.tcl |  85 +++++++++
 4 files changed, 349 insertions(+), 1 deletion(-)
 create mode 100644 tests/modules/blockonkeys.c
 create mode 100644 tests/unit/moduleapi/blockonkeys.tcl

diff --git a/runtest-moduleapi b/runtest-moduleapi
index 9301002c9..e48535126 100755
--- a/runtest-moduleapi
+++ b/runtest-moduleapi
@@ -21,4 +21,5 @@ $TCLSH tests/test_helper.tcl \
 --single unit/moduleapi/propagate \
 --single unit/moduleapi/hooks \
 --single unit/moduleapi/misc \
+--single unit/moduleapi/blockonkeys \
 "${@}"
diff --git a/tests/modules/Makefile b/tests/modules/Makefile
index 71c0b5ef8..9e27758a2 100644
--- a/tests/modules/Makefile
+++ b/tests/modules/Makefile
@@ -18,7 +18,8 @@ TEST_MODULES = \
     infotest.so \
     propagate.so \
     misc.so \
-    hooks.so
+    hooks.so \
+    blockonkeys.so
 
 .PHONY: all
 
diff --git a/tests/modules/blockonkeys.c b/tests/modules/blockonkeys.c
new file mode 100644
index 000000000..959918b1c
--- /dev/null
+++ b/tests/modules/blockonkeys.c
@@ -0,0 +1,261 @@
+#define REDISMODULE_EXPERIMENTAL_API
+#include "redismodule.h"
+
+#include <string.h>
+#include <assert.h>
+#include <unistd.h>
+
+#define LIST_SIZE 1024
+
+typedef struct {
+    long long list[LIST_SIZE];
+    long long length;
+} fsl_t; /* Fixed-size list */
+
+static RedisModuleType *fsltype = NULL;
+
+fsl_t *fsl_type_create() {
+    fsl_t *o;
+    o = RedisModule_Alloc(sizeof(*o));
+    o->length = 0;
+    return o;
+}
+
+void fsl_type_free(fsl_t *o) {
+    RedisModule_Free(o);
+}
+
+/* ========================== "fsltype" type methods ======================= */
+
+void *fsl_rdb_load(RedisModuleIO *rdb, int encver) {
+    if (encver != 0) {
+        return NULL;
+    }
+    fsl_t *fsl = fsl_type_create();
+    fsl->length = RedisModule_LoadUnsigned(rdb);
+    for (long long i = 0; i < fsl->length; i++)
+        fsl->list[i] = RedisModule_LoadSigned(rdb);
+    return fsl;
+}
+
+void fsl_rdb_save(RedisModuleIO *rdb, void *value) {
+    fsl_t *fsl = value;
+    RedisModule_SaveUnsigned(rdb,fsl->length);
+    for (long long i = 0; i < fsl->length; i++)
+        RedisModule_SaveSigned(rdb, fsl->list[i]);
+}
+
+void fsl_aofrw(RedisModuleIO *aof, RedisModuleString *key, void *value) {
+    fsl_t *fsl = value;
+    for (long long i = 0; i < fsl->length; i++)
+        RedisModule_EmitAOF(aof, "FSL.PUSH","sl", key, fsl->list[i]);
+}
+
+void fsl_free(void *value) {
+    fsl_type_free(value);
+}
+
+/* ========================== helper methods ======================= */
+
+int get_fsl(RedisModuleCtx *ctx, RedisModuleString *keyname, int mode, int create, fsl_t **fsl, int reply_on_failure) {
+    RedisModuleKey *key = RedisModule_OpenKey(ctx, keyname, mode);
+
+    int type = RedisModule_KeyType(key);
+    if (type != REDISMODULE_KEYTYPE_EMPTY && RedisModule_ModuleTypeGetType(key) != fsltype) {
+        RedisModule_CloseKey(key);
+        if (reply_on_failure)
+            RedisModule_ReplyWithError(ctx, REDISMODULE_ERRORMSG_WRONGTYPE);
+        return 0;
+    }
+
+    /* Create an empty value object if the key is currently empty. */
+    if (type == REDISMODULE_KEYTYPE_EMPTY) {
+        if (!create) {
+            /* Key is empty but we cannot create */
+            RedisModule_CloseKey(key);
+            *fsl = NULL;
+            return 1;
+        }
+        *fsl = fsl_type_create();
+        RedisModule_ModuleTypeSetValue(key, fsltype, *fsl);
+    } else {
+        *fsl = RedisModule_ModuleTypeGetValue(key);
+    }
+
+    RedisModule_CloseKey(key);
+    return 1;
+}
+
+/* ========================== commands ======================= */
+
+/* FSL.PUSH <key> <int> - Push an integer to the fixed-size list (to the right).
+ * It must be greater than the element in the head of the list. */
+int fsl_push(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 3)
+        return RedisModule_WrongArity(ctx);
+
+    long long ele;
+    if (RedisModule_StringToLongLong(argv[2],&ele) != REDISMODULE_OK)
+        return RedisModule_ReplyWithError(ctx,"ERR invalid integer");
+
+    fsl_t *fsl;
+    if (!get_fsl(ctx, argv[1], REDISMODULE_WRITE, 1, &fsl, 1))
+        return REDISMODULE_OK;
+
+    if (fsl->length == LIST_SIZE)
+        return RedisModule_ReplyWithError(ctx,"ERR list is full");
+
+    if (fsl->length != 0 && fsl->list[fsl->length-1] >= ele)
+        return RedisModule_ReplyWithError(ctx,"ERR new element has to be greater than the head element");
+
+    fsl->list[fsl->length++] = ele;
+
+    if (fsl->length >= 2)
+        RedisModule_SignalKeyAsReady(ctx, argv[1]);
+
+    return RedisModule_ReplyWithSimpleString(ctx, "OK");
+}
+
+int bpop2_reply_callback(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+    RedisModuleString *keyname = RedisModule_GetBlockedClientReadyKey(ctx);
+
+    fsl_t *fsl;
+    if (!get_fsl(ctx, keyname, REDISMODULE_READ, 0, &fsl, 0))
+        return REDISMODULE_ERR;
+
+    if (!fsl || fsl->length < 2)
+        return REDISMODULE_ERR;
+
+    RedisModule_ReplyWithArray(ctx, 2);
+    RedisModule_ReplyWithLongLong(ctx, fsl->list[--fsl->length]);
+    RedisModule_ReplyWithLongLong(ctx, fsl->list[--fsl->length]);
+    return REDISMODULE_OK;
+}
+
+int bpop2_timeout_callback(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+    return RedisModule_ReplyWithSimpleString(ctx, "Request timedout");
+}
+
+
+/* FSL.BPOP2 <key> <timeout> - Block clients until list has two or more elements.
+ * When that happens, unblock client and pop the last two elements (from the right). */
+int fsl_bpop2(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 3)
+        return RedisModule_WrongArity(ctx);
+
+    long long timeout;
+    if (RedisModule_StringToLongLong(argv[2],&timeout) != REDISMODULE_OK || timeout < 0)
+        return RedisModule_ReplyWithError(ctx,"ERR invalid timeout");
+
+    fsl_t *fsl;
+    if (!get_fsl(ctx, argv[1], REDISMODULE_READ, 0, &fsl, 1))
+        return REDISMODULE_OK;
+
+    if (!fsl || fsl->length < 2) {
+        /* Key is empty or has <2 elements, we must block */
+        RedisModule_BlockClientOnKeys(ctx, bpop2_reply_callback, bpop2_timeout_callback,
+                                      NULL, timeout, &argv[1], 1, NULL);
+    } else {
+        RedisModule_ReplyWithArray(ctx, 2);
+        RedisModule_ReplyWithLongLong(ctx, fsl->list[--fsl->length]);
+        RedisModule_ReplyWithLongLong(ctx, fsl->list[--fsl->length]);
+    }
+
+    return REDISMODULE_OK;
+}
+
+int bpopgt_reply_callback(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+    RedisModuleString *keyname = RedisModule_GetBlockedClientReadyKey(ctx);
+    long long gt = (long long)RedisModule_GetBlockedClientPrivateData(ctx);
+
+    fsl_t *fsl;
+    if (!get_fsl(ctx, keyname, REDISMODULE_READ, 0, &fsl, 0))
+        return REDISMODULE_ERR;
+
+    if (!fsl || fsl->list[fsl->length-1] <= gt)
+        return REDISMODULE_ERR;
+
+    RedisModule_ReplyWithLongLong(ctx, fsl->list[--fsl->length]);
+    return REDISMODULE_OK;
+}
+
+int bpopgt_timeout_callback(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+    return RedisModule_ReplyWithSimpleString(ctx, "Request timedout");
+}
+
+void bpopgt_free_privdata(RedisModuleCtx *ctx, void *privdata) {
+    /* Nothing to do because privdata is actually a 'long long',
+     * not a pointer to the heap */
+    REDISMODULE_NOT_USED(ctx);
+    REDISMODULE_NOT_USED(privdata);
+}
+
+/* FSL.BPOPGT <key> <gt> <timeout> - Block clients until list has an element greater than <gt>.
+ * When that happens, unblock client and pop the last element (from the right). */
+int fsl_bpopgt(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc != 4)
+        return RedisModule_WrongArity(ctx);
+
+    long long gt;
+    if (RedisModule_StringToLongLong(argv[2],&gt) != REDISMODULE_OK)
+        return RedisModule_ReplyWithError(ctx,"ERR invalid integer");
+
+    long long timeout;
+    if (RedisModule_StringToLongLong(argv[3],&timeout) != REDISMODULE_OK || timeout < 0)
+        return RedisModule_ReplyWithError(ctx,"ERR invalid timeout");
+
+    fsl_t *fsl;
+    if (!get_fsl(ctx, argv[1], REDISMODULE_READ, 0, &fsl, 1))
+        return REDISMODULE_OK;
+
+    if (!fsl || fsl->list[fsl->length-1] <= gt) {
+        /* Key is empty or has <2 elements, we must block */
+        RedisModule_BlockClientOnKeys(ctx, bpopgt_reply_callback, bpopgt_timeout_callback,
+                                      bpopgt_free_privdata, timeout, &argv[1], 1, (void*)gt);
+    } else {
+        RedisModule_ReplyWithLongLong(ctx, fsl->list[--fsl->length]);
+    }
+
+    return REDISMODULE_OK;
+}
+
+int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+
+    if (RedisModule_Init(ctx, "blockonkeys", 1, REDISMODULE_APIVER_1)== REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    RedisModuleTypeMethods tm = {
+        .version = REDISMODULE_TYPE_METHOD_VERSION,
+        .rdb_load = fsl_rdb_load,
+        .rdb_save = fsl_rdb_save,
+        .aof_rewrite = fsl_aofrw,
+        .mem_usage = NULL,
+        .free = fsl_free,
+        .digest = NULL
+    };
+
+    fsltype = RedisModule_CreateDataType(ctx, "fsltype_t", 0, &tm);
+    if (fsltype == NULL)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"fsl.push",fsl_push,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"fsl.bpop2",fsl_bpop2,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"fsl.bpopgt",fsl_bpopgt,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    return REDISMODULE_OK;
+}
diff --git a/tests/unit/moduleapi/blockonkeys.tcl b/tests/unit/moduleapi/blockonkeys.tcl
new file mode 100644
index 000000000..cb99ab1c9
--- /dev/null
+++ b/tests/unit/moduleapi/blockonkeys.tcl
@@ -0,0 +1,85 @@
+set testmodule [file normalize tests/modules/blockonkeys.so]
+
+start_server {tags {"modules"}} {
+    r module load $testmodule
+
+    test {Module client blocked on keys (no metadata): No block} {
+        r del k
+        r fsl.push k 33
+        r fsl.push k 34
+        r fsl.bpop2 k 0
+    } {34 33}
+
+    test {Module client blocked on keys (no metadata): Timeout} {
+        r del k
+        set rd [redis_deferring_client]
+        r fsl.push k 33
+        $rd fsl.bpop2 k 1
+        assert_equal {Request timedout} [$rd read]
+    }
+
+    test {Module client blocked on keys (no metadata): Blocked, case 1} {
+        r del k
+        set rd [redis_deferring_client]
+        r fsl.push k 33
+        $rd fsl.bpop2 k 0
+        r fsl.push k 34
+        assert_equal {34 33} [$rd read]
+    }
+
+    test {Module client blocked on keys (no metadata): Blocked, case 2} {
+        r del k
+        set rd [redis_deferring_client]
+        r fsl.push k 33
+        r fsl.push k 34
+        $rd fsl.bpop2 k 0
+        assert_equal {34 33} [$rd read]
+    }
+
+    test {Module client blocked on keys (with metadata): No block} {
+        r del k
+        r fsl.push k 34
+        r fsl.bpopgt k 30 0
+    } {34}
+
+    test {Module client blocked on keys (with metadata): Timeout} {
+        r del k
+        set rd [redis_deferring_client]
+        r fsl.push k 33
+        $rd fsl.bpopgt k 35 1
+        assert_equal {Request timedout} [$rd read]
+    }
+
+    test {Module client blocked on keys (with metadata): Blocked, case 1} {
+        r del k
+        set rd [redis_deferring_client]
+        r fsl.push k 33
+        $rd fsl.bpopgt k 33 0
+        r fsl.push k 34
+        assert_equal {34} [$rd read]
+    }
+
+    test {Module client blocked on keys (with metadata): Blocked, case 2} {
+        r del k
+        set rd [redis_deferring_client]
+        $rd fsl.bpopgt k 35 0
+        r fsl.push k 33
+        r fsl.push k 34
+        r fsl.push k 35
+        r fsl.push k 36
+        assert_equal {36} [$rd read]
+    }
+
+    test {Module client blocked on keys does not wake up on wrong type} {
+        r del k
+        set rd [redis_deferring_client]
+        $rd fsl.bpop2 k 0
+        r lpush k 12
+        r lpush k 13
+        r lpush k 14
+        r del k
+        r fsl.push k 33
+        r fsl.push k 34
+        assert_equal {34 33} [$rd read]
+    }
+}