Fix potential data race in mutex lock implementation.

src/Common/MutexLock.hpp

@@ -59,6 +59,8 @@ namespace sw
 
 #else   // !__ANDROID__
 
+#include <atomic>
+
 namespace sw
 {
 	class BackoffLock
@@ -73,7 +75,7 @@ namespace sw
 		{
 			if(!isLocked())
 			{
-				if(atomicExchange(&mutex, 1) == 0)
+				if(mutex.exchange(true) == false)
 				{
 					return true;
 				}
@@ -148,12 +150,12 @@ namespace sw
 
 		void unlock()
 		{
-			mutex = 0;
+			mutex.store(false, std::memory_order_release);
 		}
 
 		bool isLocked()
 		{
-			return mutex != 0;
+			return mutex.load(std::memory_order_acquire);
 		}
 
 	private:
@@ -162,7 +164,7 @@ namespace sw
 			// Ensure that the mutex variable is on its own 64-byte cache line to avoid false sharing
 			// Padding must be public to avoid compiler warnings
 			volatile int padding1[16];
-			volatile int mutex;
+			std::atomic<bool> mutex;
 			volatile int padding2[15];
 		};
 	};