Update PR #6537 patch to for generality.

After the thread in #6537 and thanks to the suggestions received, this
commit updates the original patch in order to:

1. Solve the problem of updating the time in multiple places by updating
it in call().
2. Avoid introducing a new field but use our cached time.

This required some minor refactoring to the function updating the time,
and the introduction of a new cached time in microseconds in order to
use less gettimeofday() calls.

src/db.c

@@ -1198,8 +1198,12 @@ int keyIsExpired(redisDb *db, robj *key) {
      * blocked to when the Lua script started. This way a key can expire
      * only the first time it is accessed and not in the middle of the
      * script execution, making propagation to slaves / AOF consistent.
-     * See issue #1525 on Github for more information. */
-    mstime_t now = server.lua_caller ? server.lua_time_start : server.cmd_start_mstime;
+     * See issue #1525 on Github for more information.
+     *
+     * Outside the Lua script execution, we use the cached time server.mstime
+     * that is updated before commands executions in call(). */
+    mstime_t now = server.lua_caller ? server.lua_time_start :
+                                       server.mstime;
 
     return now > when;
 }

src/rdb.c

@@ -1961,7 +1961,7 @@ void rdbLoadProgressCallback(rio *r, const void *buf, size_t len) {
         /* The DB can take some non trivial amount of time to load. Update
          * our cached time since it is used to create and update the last
          * interaction time with clients and for other important things. */
-        updateCachedTime();
+        updateCachedTime(0);
         if (server.masterhost && server.repl_state == REPL_STATE_TRANSFER)
             replicationSendNewlineToMaster();
         loadingProgress(r->processed_bytes);

src/server.c

@@ -1736,20 +1736,29 @@ void databasesCron(void) {
 /* We take a cached value of the unix time in the global state because with
  * virtual memory and aging there is to store the current time in objects at
  * every object access, and accuracy is not needed. To access a global var is
- * a lot faster than calling time(NULL) */
-void updateCachedTime(void) {
-    server.unixtime = time(NULL);
-    server.mstime = mstime();
+ * a lot faster than calling time(NULL).
+ *
+ * This function should be fast because it is called at every command execution
+ * in call(), so it is possible to decide if to update the daylight saving
+ * info or not using the 'update_daylight_info' argument. Normally we update
+ * such info only when calling this function from serverCron() but not when
+ * calling it from call(). */
+void updateCachedTime(int update_daylight_info) {
+    server.ustime = ustime();
+    server.mstime = server.ustime / 1000;
+    server.unixtime = server.mstime / 1000;
 
     /* To get information about daylight saving time, we need to call
      * localtime_r and cache the result. However calling localtime_r in this
      * context is safe since we will never fork() while here, in the main
      * thread. The logging function will call a thread safe version of
      * localtime that has no locks. */
-    struct tm tm;
-    time_t ut = server.unixtime;
-    localtime_r(&ut,&tm);
-    server.daylight_active = tm.tm_isdst;
+    if (update_daylight_info) {
+        struct tm tm;
+        time_t ut = server.unixtime;
+        localtime_r(&ut,&tm);
+        server.daylight_active = tm.tm_isdst;
+    }
 }
 
 void checkChildrenDone(void) {
@@ -1838,7 +1847,7 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
     if (server.watchdog_period) watchdogScheduleSignal(server.watchdog_period);
 
     /* Update the time cache. */
-    updateCachedTime();
+    updateCachedTime(1);
 
     server.hz = server.config_hz;
     /* Adapt the server.hz value to the number of configured clients. If we have
@@ -2252,7 +2261,7 @@ void createSharedObjects(void) {
 void initServerConfig(void) {
     int j;
 
-    updateCachedTime();
+    updateCachedTime(1);
     getRandomHexChars(server.runid,CONFIG_RUN_ID_SIZE);
     server.runid[CONFIG_RUN_ID_SIZE] = '\0';
     changeReplicationId();
@@ -3238,7 +3247,8 @@ void preventCommandReplication(client *c) {
  *
  */
 void call(client *c, int flags) {
-    long long dirty, start, duration;
+    long long dirty;
+    ustime_t start, duration;
     int client_old_flags = c->flags;
     struct redisCommand *real_cmd = c->cmd;
 
@@ -3259,7 +3269,8 @@ void call(client *c, int flags) {
 
     /* Call the command. */
     dirty = server.dirty;
-    start = ustime();
+    updateCachedTime(0);
+    start = server.ustime;
     c->cmd->proc(c);
     duration = ustime()-start;
     dirty = server.dirty-dirty;
@@ -3596,7 +3607,6 @@ int processCommand(client *c) {
         queueMultiCommand(c);
         addReply(c,shared.queued);
     } else {
-        server.cmd_start_mstime = mstime();
         call(c,CMD_CALL_FULL);
         c->woff = server.master_repl_offset;
         if (listLength(server.ready_keys))

src/server.h

@@ -50,6 +50,7 @@
 #include <signal.h>
 
 typedef long long mstime_t; /* millisecond time type. */
+typedef long long ustime_t; /* microsecond time type. */
 
 #include "ae.h"      /* Event driven programming library */
 #include "sds.h"     /* Dynamic safe strings */
@@ -1400,8 +1401,8 @@ struct redisServer {
     _Atomic time_t unixtime;    /* Unix time sampled every cron cycle. */
     time_t timezone;            /* Cached timezone. As set by tzset(). */
     int daylight_active;        /* Currently in daylight saving time. */
-    long long mstime;           /* 'unixtime' with milliseconds resolution. */
-    mstime_t cmd_start_mstime;
+    mstime_t mstime;            /* 'unixtime' in milliseconds. */
+    ustime_t ustime;            /* 'unixtime' in microseconds. */
     /* Pubsub */
     dict *pubsub_channels;  /* Map channels to list of subscribed clients */
     list *pubsub_patterns;  /* A list of pubsub_patterns */
@@ -1997,7 +1998,7 @@ void populateCommandTable(void);
 void resetCommandTableStats(void);
 void adjustOpenFilesLimit(void);
 void closeListeningSockets(int unlink_unix_socket);
-void updateCachedTime(void);
+void updateCachedTime(int update_daylight_info);
 void resetServerStats(void);
 void activeDefragCycle(void);
 unsigned int getLRUClock(void);