Implement use-fork config (fails with diskless repl)

Former-commit-id: f2d5c2bca22e9fd506db123c47b7f60cdded7e2c

src/config.cpp

@@ -2308,6 +2308,7 @@ standardConfig configs[] = {
     createBoolConfig("delete-on-evict", NULL, MODIFIABLE_CONFIG, cserver.delete_on_evict, 0, NULL, NULL),
     createBoolConfig("io-threads-do-reads", NULL, IMMUTABLE_CONFIG, fDummy, 0,NULL, NULL),     // Not applicable to KeyDB, just there for compatibility
     createBoolConfig("multi-master-no-forward", NULL, MODIFIABLE_CONFIG, cserver.multimaster_no_forward, 0, validateMultiMasterNoForward, NULL),
+    createBoolConfig("use-fork", NULL, IMMUTABLE_CONFIG, cserver.fForkBgSave, 0, NULL, NULL),
 
     /* String Configs */
     createStringConfig("aclfile", NULL, IMMUTABLE_CONFIG, ALLOW_EMPTY_STRING, g_pserver->acl_filename, "", NULL, NULL),

src/rdb.cpp

@@ -1492,8 +1492,52 @@ void *rdbSaveThread(void *vargs)
     return (retval == C_OK) ? (void*)0 : (void*)1;
 }
 
+int rdbSaveBackgroundFork(rdbSaveInfo *rsi) {
+    pid_t childpid;
+
+    if (hasActiveChildProcess() || g_pserver->rdb_child_pid != -1) return C_ERR;
+    serverAssert(g_pserver->rdb_child_pid != 10000);
+
+    g_pserver->dirty_before_bgsave = g_pserver->dirty;
+    g_pserver->lastbgsave_try = time(NULL);
+    openChildInfoPipe();
+
+    if ((childpid = redisFork()) == 0) {
+        int retval;
+
+        /* Child */
+        g_pserver->rdb_child_pid = 10000;
+        redisSetProcTitle("keydb-rdb-bgsave");
+        redisSetCpuAffinity(g_pserver->bgsave_cpulist);
+        retval = rdbSave(nullptr, rsi);
+        if (retval == C_OK) {
+            sendChildCOWInfo(CHILD_INFO_TYPE_RDB, "RDB");
+        }
+        exitFromChild((retval == C_OK) ? 0 : 1);
+    } else {
+        /* Parent */
+        if (childpid == -1) {
+            closeChildInfoPipe();
+            g_pserver->lastbgsave_status = C_ERR;
+            serverLog(LL_WARNING,"Can't save in background: fork: %s",
+                strerror(errno));
+            return C_ERR;
+        }
+        serverLog(LL_NOTICE,"Background saving started by pid %d",childpid);
+        g_pserver->rdb_save_time_start = time(NULL);
+        g_pserver->rdb_child_pid = childpid;
+        g_pserver->rdb_child_type = RDB_CHILD_TYPE_DISK;
+        return C_OK;
+    }
+    return C_OK; /* unreached */
+}
+
 int launchRdbSaveThread(pthread_t &child, rdbSaveInfo *rsi)
 {
+    if (cserver.fForkBgSave) {
+        return rdbSaveBackgroundFork(rsi);
+    } else
+    {
         rdbSaveThreadArgs *args = (rdbSaveThreadArgs*)zmalloc(sizeof(rdbSaveThreadArgs) + ((cserver.dbnum-1)*sizeof(redisDbPersistentDataSnapshot*)), MALLOC_LOCAL);
         rdbSaveInfo rsiT = RDB_SAVE_INFO_INIT;
         if (rsi == nullptr)
@@ -1513,9 +1557,11 @@ int launchRdbSaveThread(pthread_t &child, rdbSaveInfo *rsi)
             zfree(args);
             return C_ERR;
         }
+    }
     return C_OK;
 }
 
+
 int rdbSaveBackground(rdbSaveInfo *rsi) {
     pthread_t child;
     long long start;
@@ -2743,6 +2789,13 @@ void backgroundSaveDoneHandler(int exitcode, bool fCancelled) {
  * the cleanup needed. */
 void killRDBChild(bool fSynchronous) {
     serverAssert(GlobalLocksAcquired());
+
+    if (cserver.fForkBgSave) {
+        kill(g_pserver->rdb_child_pid,SIGUSR1);
+        rdbRemoveTempFile(g_pserver->rdb_child_pid);
+        closeChildInfoPipe();
+        updateDictResizePolicy();
+    } else { 
         g_pserver->rdbThreadVars.fRdbThreadCancel = true;
         rdbRemoveTempFile(g_pserver->rdbThreadVars.tmpfileNum);
         closeChildInfoPipe();
@@ -2756,6 +2809,7 @@ void killRDBChild(bool fSynchronous) {
             g_pserver->rdbThreadVars.fRdbThreadCancel = false;
             aeAcquireLock();
         }
+    }
 }
 
 struct rdbSaveSocketThreadArgs

src/server.cpp

@@ -1554,7 +1554,7 @@ int redisDbPersistentData::incrementallyRehash() {
  * for dict.c to resize the hash tables accordingly to the fact we have o not
  * running childs. */
 void updateDictResizePolicy(void) {
-    if (!hasActiveChildProcess() || g_pserver->FRdbSaveInProgress())
+    if (!hasActiveChildProcess() || (g_pserver->FRdbSaveInProgress() && !cserver.fForkBgSave))
         dictEnableResize();
     else
         dictDisableResize();
@@ -1946,7 +1946,7 @@ void checkChildrenDone(void) {
     if (g_pserver->FRdbSaveInProgress() && g_pserver->rdb_pipe_conns)
         return;
 
-    if (g_pserver->FRdbSaveInProgress())
+    if (g_pserver->FRdbSaveInProgress() && !cserver.fForkBgSave)
     {
         void *rval = nullptr;
         int err;
@@ -1985,6 +1985,11 @@ void checkChildrenDone(void) {
                 strerror(errno),
                 (int) g_pserver->aof_child_pid,
                 (int) g_pserver->module_child_pid);
+        } else if (pid == g_pserver->rdb_child_pid) {
+            backgroundSaveDoneHandler(exitcode,bysignal == SIGUSR1);
+            g_pserver->rdbThreadVars.fRdbThreadCancel = false;
+            g_pserver->rdb_child_pid = -1;
+            if (exitcode == 0) receiveChildInfo();
         } else if (pid == g_pserver->aof_child_pid) {
             backgroundRewriteDoneHandler(exitcode,bysignal);
             if (!bysignal && exitcode == 0) receiveChildInfo();

src/server.h

@@ -2130,6 +2130,7 @@ struct redisServerConst {
     int multimaster_no_forward;
     int storage_memory_model = STORAGE_WRITETHROUGH;
     char *storage_conf = nullptr;
+    int fForkBgSave = false;
 };
 
 struct redisServer {
@@ -2297,6 +2298,7 @@ struct redisServer {
     time_t lastbgsave_try;          /* Unix time of last attempted bgsave */
     time_t rdb_save_time_last;      /* Time used by last RDB save run. */
     time_t rdb_save_time_start;     /* Current RDB save start time. */
+    pid_t rdb_child_pid = -1;            /* Used only during fork bgsave */
     int rdb_bgsave_scheduled;       /* BGSAVE when possible if true. */
     int rdb_child_type;             /* Type of save by active child. */
     int lastbgsave_status;          /* C_OK or C_ERR */

tests/unit/introspection.tcl

@@ -101,6 +101,7 @@ start_server {tags {"introspection"}} {
             bgsave_cpulist
 	    storage-cache-mode
 	    storage-provider-options
+	    use-fork
         }
 
         set configs {}