Merge pull request #34598 from mikeash/os-unfair-lock-mutex

[Runtime] Use os_unfair_lock for Mutex and StaticMutex on Darwin.

stdlib/public/runtime/MetadataCache.h

@@ -100,7 +100,7 @@ enum class ConcurrencyRequest {
 };
 
 struct ConcurrencyControl {
-  Mutex Lock;
+  ConditionVariable::Mutex Lock;
   ConditionVariable Queue;
 
   ConcurrencyControl() = default;

stdlib/public/runtime/MutexPThread.cpp

@@ -114,6 +114,29 @@ bool MutexPlatformHelper::try_lock(pthread_mutex_t &mutex) {
                           /* returnFalseOnEBUSY = */ true);
 }
 
+#if HAS_OS_UNFAIR_LOCK
+
+void MutexPlatformHelper::init(os_unfair_lock &lock, bool checked) {
+  (void)checked; // Unfair locks are always checked.
+  lock = OS_UNFAIR_LOCK_INIT;
+}
+
+void MutexPlatformHelper::destroy(os_unfair_lock &lock) {}
+
+void MutexPlatformHelper::lock(os_unfair_lock &lock) {
+  os_unfair_lock_lock(&lock);
+}
+
+void MutexPlatformHelper::unlock(os_unfair_lock &lock) {
+  os_unfair_lock_unlock(&lock);
+}
+
+bool MutexPlatformHelper::try_lock(os_unfair_lock &lock) {
+  return os_unfair_lock_trylock(&lock);
+}
+
+#endif
+
 void ReadWriteLockPlatformHelper::init(pthread_rwlock_t &rwlock) {
   reportError(pthread_rwlock_init(&rwlock, nullptr));
 }