Init GlobalThreadPool in a thread safe manner

Common/ThreadPools.cpp

@@ -1,18 +1,16 @@
 #include "ThreadPools.h"
 
 #include "../Core/Config.h"
+#include "Common/MakeUnique.h"
 
-std::shared_ptr<ThreadPool> GlobalThreadPool::pool;
-bool  GlobalThreadPool::initialized = false;
+std::unique_ptr<ThreadPool> GlobalThreadPool::pool;
+std::once_flag GlobalThreadPool::init_flag;
 
 void GlobalThreadPool::Loop(const std::function<void(int,int)>& loop, int lower, int upper) {
-	Inititialize();
+	std::call_once(init_flag, Inititialize);
 	pool->ParallelLoop(loop, lower, upper);
 }
 
 void GlobalThreadPool::Inititialize() {
-	if(!initialized) {
-		pool = std::make_shared<ThreadPool>(g_Config.iNumWorkerThreads);
-		initialized = true;
-	}
+	pool = make_unique<ThreadPool>(g_Config.iNumWorkerThreads);
 }