Use threadpool for CreateNewInstancesForPlayers.

src/game/Maps/MapManager.cpp

@@ -42,10 +42,12 @@ MapManager::MapManager()
     :
     i_gridCleanUpDelay(sWorld.getConfig(CONFIG_UINT32_INTERVAL_GRIDCLEAN)),
     i_MaxInstanceId(RESERVED_INSTANCES_LAST),
-    m_threads(new ThreadPool(sWorld.getConfig(CONFIG_UINT32_MAPUPDATE_INSTANCED_UPDATE_THREADS)))
+    m_threads(new ThreadPool(sWorld.getConfig(CONFIG_UINT32_MAPUPDATE_INSTANCED_UPDATE_THREADS))),
+    m_instanceCreationThreads(new ThreadPool(1))
 {
     i_timer.SetInterval(sWorld.getConfig(CONFIG_UINT32_INTERVAL_MAPUPDATE));
     m_threads->start<ThreadPool::MySQL<>>();
+    m_instanceCreationThreads->start<>();
 }
 
 MapManager::~MapManager()
@@ -336,7 +338,10 @@ void MapManager::Update(uint32 diff)
         }
     }
 
-    std::thread instanceCreationThread = std::thread(&MapManager::CreateNewInstancesForPlayers, this);
+    std::vector<std::function<void()>> instanceCreators;
+    instanceCreators.emplace_back([this]() {CreateNewInstancesForPlayers();});
+    std::future<void> instances = m_instanceCreationThreads->processWorkload(std::move(instanceCreators),
+        ThreadPool::Callable());
 
     i_maxContinentThread = continentsIdx;
     i_continentUpdateFinished.store(0);
@@ -367,8 +372,8 @@ void MapManager::Update(uint32 diff)
     SwitchPlayersInstances();
     asyncMapUpdating = false;
 
-    if (instanceCreationThread.joinable())
-        instanceCreationThread.join();
+    if (instances.valid())
+        instances.wait();
 
     // Execute far teleports after all map updates have finished
     ExecuteDelayedPlayerTeleports();

src/game/Maps/MapManager.h

@@ -225,6 +225,7 @@ class MapManager : public MaNGOS::Singleton<MapManager, MaNGOS::ClassLevelLockab
 
         std::unique_ptr<ThreadPool> m_threads;
         std::unique_ptr<ThreadPool> m_continentThreads;
+        std::unique_ptr<ThreadPool> m_instanceCreationThreads;
         bool asyncMapUpdating = false;
 
         // Instanced continent zones