Merge pull request #7965 from jordan-woyak/condvar-fixes

Minor changes to usages of std::condition_variable.

Source/Core/AudioCommon/AlsaSoundStream.cpp

@@ -19,6 +19,9 @@ AlsaSound::~AlsaSound()
 {
   m_thread_status.store(ALSAThreadStatus::STOPPING);
 
+  // Immediately lock and unlock mutex to prevent cv race.
+  std::unique_lock<std::mutex>{cv_m};
+
   // Give the opportunity to the audio thread
   // to realize we are stopping the emulation
   cv.notify_one();
@@ -81,7 +84,12 @@ void AlsaSound::SoundLoop()
 bool AlsaSound::SetRunning(bool running)
 {
   m_thread_status.store(running ? ALSAThreadStatus::RUNNING : ALSAThreadStatus::PAUSED);
-  cv.notify_one();  // Notify thread that status has changed
+
+  // Immediately lock and unlock mutex to prevent cv race.
+  std::unique_lock<std::mutex>{cv_m};
+
+  // Notify thread that status has changed
+  cv.notify_one();
   return true;
 }
 

Source/Core/Common/Event.h

@@ -31,7 +31,18 @@ public:
   {
     if (m_flag.TestAndSet())
     {
-      std::lock_guard<std::mutex> lk(m_mutex);
+      // Lock and immediately unlock m_mutex.
+      {
+        // Holding the lock at any time between the change of our flag and notify call
+        // is sufficient to prevent a race where both of these actions
+        // happen between the other thread's predicate test and wait call
+        // which would cause wait to block until the next spurious wakeup or timeout.
+
+        // Unlocking before notification is a micro-optimization to prevent
+        // the notified thread from immediately blocking on the mutex.
+        std::lock_guard<std::mutex> lk(m_mutex);
+      }
+
       m_condvar.notify_one();
     }
   }

Source/Core/VideoCommon/RenderBase.h

@@ -15,7 +15,6 @@
 #pragma once
 
 #include <array>
-#include <condition_variable>
 #include <memory>
 #include <mutex>
 #include <string>