Bug 1407810 - Make DecoderDoctorLogger::sLogState 'ReleaseAcquire' - r=jwwang

sLogState is accessed at least once for every DDLog call, even when logging is
disabled, so we want it to be as quick as possible for minimal impact on most
users.

MozReview-Commit-ID: AMstgXmixrv

--HG--
extra : rebase_source : 475b32f76d9660d03333047eb7e7add62b717a79

dom/media/doctor/DecoderDoctorLogger.cpp

@@ -14,7 +14,7 @@
 
 namespace mozilla {
 
-/* static */ Atomic<DecoderDoctorLogger::LogState>
+/* static */ Atomic<DecoderDoctorLogger::LogState, ReleaseAcquire>
   DecoderDoctorLogger::sLogState{ DecoderDoctorLogger::scDisabled };
 
 /* static */ const char* DecoderDoctorLogger::sShutdownReason = nullptr;

dom/media/doctor/DecoderDoctorLogger.h

@@ -346,7 +346,9 @@ private:
   // Shutdown, cannot be re-enabled.
   static constexpr LogState scShutdown = 3;
   // Current state.
-  static Atomic<LogState> sLogState;
+  // "ReleaseAcquire" because when changing to scEnabled, the just-created
+  // sMediaLogs must be accessible to consumers that see scEnabled.
+  static Atomic<LogState, ReleaseAcquire> sLogState;
 
   // If non-null, reason for an abnormal shutdown.
   static const char* sShutdownReason;