Guard against race in perf warnings.

src/common/debug.cpp

@@ -14,7 +14,6 @@
 #include <cstdio>
 #include <cstring>
 #include <fstream>
-#include <mutex>
 #include <ostream>
 #include <vector>
 
@@ -114,6 +113,12 @@ void InitializeDebugMutexIfNeeded()
     }
 }
 
+std::mutex &GetDebugMutex()
+{
+    ASSERT(g_debugMutex);
+    return *g_debugMutex;
+}
+
 ScopedPerfEventHelper::ScopedPerfEventHelper(const char *format, ...) : mFunctionName(nullptr)
 {
     bool dbgTrace = DebugAnnotationsActive();

src/common/debug.h

@@ -15,6 +15,7 @@
 
 #include <iomanip>
 #include <ios>
+#include <mutex>
 #include <sstream>
 #include <string>
 
@@ -103,6 +104,8 @@ bool DebugAnnotationsInitialized();
 
 void InitializeDebugMutexIfNeeded();
 
+std::mutex &GetDebugMutex();
+
 namespace priv
 {
 // This class is used to explicitly ignore values in the conditional logging macros. This avoids

src/libANGLE/Debug.cpp

@@ -340,18 +340,28 @@ size_t Debug::getGroupStackDepth() const
 
 void Debug::insertPerfWarning(GLenum severity, const char *message, uint32_t *repeatCount) const
 {
+    bool repeatLast;
+
+    {
         constexpr uint32_t kMaxRepeat = 4;
+        std::lock_guard<std::mutex> lock(GetDebugMutex());
+
         if (*repeatCount >= kMaxRepeat)
         {
             return;
         }
 
         ++*repeatCount;
+        repeatLast = (*repeatCount == kMaxRepeat);
+    }
+
     std::string msg = message;
-    if (*repeatCount == kMaxRepeat)
+    if (repeatLast)
     {
         msg += " (this message will no longer repeat)";
     }
+
+    // Release the lock before we call insertMessage. It will re-acquire the lock.
     insertMessage(GL_DEBUG_SOURCE_API, GL_DEBUG_TYPE_PERFORMANCE, 0, severity, std::move(msg),
                   gl::LOG_INFO);
 }