Change server.daylight_active to an atomic variable (#876)

We are updating this variable in the main thread, and the
child threads can printing the logs at the same time. This
generating a warning in SANITIZER=thread:
```
WARNING: ThreadSanitizer: data race (pid=74208)
  Read of size 4 at 0x000102875c10 by thread T3:
    #0 serverLogRaw <null>:52173615 (valkey-server:x86_64+0x10003c556)
    #1 _serverLog <null>:52173615 (valkey-server:x86_64+0x10003ca89)
    #2 bioProcessBackgroundJobs <null>:52173615 (valkey-server:x86_64+0x1001402c9)

  Previous write of size 4 at 0x000102875c10 by main thread (mutexes: write M0):
    #0 afterSleep <null>:52173615 (valkey-server:x86_64+0x10004989b)
    #1 aeProcessEvents <null>:52173615 (valkey-server:x86_64+0x100031e52)
    #2 main <null>:52173615 (valkey-server:x86_64+0x100064a3c)
    #3 start <null>:52173615 (dyld:x86_64+0xfffffffffff5c365)
    #4 start <null>:52173615 (dyld:x86_64+0xfffffffffff5c365)
```

The refresh of daylight_active is not real time, we update
it in aftersleep, so we don't need a strong synchronization,
so using memory_order_relaxed. But also noted we are doing
load/store operations only for daylight_active, which is an
aligned 32-bit integer, so using memory_order_relaxed will
not provide more consistency than what we have today.

So this is just a cleanup that to clear the warning.

Signed-off-by: Binbin <[email protected]>

src/server.c

@@ -131,10 +131,11 @@ void serverLogRaw(int level, const char *msg) {
         struct timeval tv;
         int role_char;
         pid_t pid = getpid();
+        int daylight_active = atomic_load_explicit(&server.daylight_active, memory_order_relaxed);
 
         gettimeofday(&tv, NULL);
         struct tm tm;
-        nolocks_localtime(&tm, tv.tv_sec, server.timezone, server.daylight_active);
+        nolocks_localtime(&tm, tv.tv_sec, server.timezone, daylight_active);
         off = strftime(buf, sizeof(buf), "%d %b %Y %H:%M:%S.", &tm);
         snprintf(buf + off, sizeof(buf) - off, "%03d", (int)tv.tv_usec / 1000);
         if (server.sentinel_mode) {
@@ -1091,7 +1092,7 @@ static inline void updateCachedTimeWithUs(int update_daylight_info, const long l
         struct tm tm;
         time_t ut = server.unixtime;
         localtime_r(&ut, &tm);
-        server.daylight_active = tm.tm_isdst;
+        atomic_store_explicit(&server.daylight_active, tm.tm_isdst, memory_order_relaxed);
     }
 }
 

src/server.h

@@ -2114,7 +2114,7 @@ struct valkeyServer {
     /* time cache */
     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. */
+    _Atomic int daylight_active; /* Currently in daylight saving time. */
     mstime_t mstime;             /* 'unixtime' in milliseconds. */
     ustime_t ustime;             /* 'unixtime' in microseconds. */
     mstime_t cmd_time_snapshot;  /* Time snapshot of the root execution nesting. */