fix CCTextureCache addImageAsync race condition (cocos2d#18366)

Author: xiaoyur347

cocos/renderer/CCTextureCache.cpp

@@ -214,8 +214,8 @@ void TextureCache::addImageAsync(const std::string &path, const std::function<vo
     if (_loadingThread == nullptr)
     {
         // create a new thread to load images
-        _loadingThread = new (std::nothrow) std::thread(&TextureCache::loadImage, this);
         _needQuit = false;
+        _loadingThread = new (std::nothrow) std::thread(&TextureCache::loadImage, this);
     }
 
     if (0 == _asyncRefCount)
@@ -231,10 +231,8 @@ void TextureCache::addImageAsync(const std::string &path, const std::function<vo
 
     // add async struct into queue
     _asyncStructQueue.push_back(data);
-    _requestMutex.lock();
+    std::unique_lock<std::mutex> ul(_requestMutex);
     _requestQueue.push_back(data);
-    _requestMutex.unlock();
-
     _sleepCondition.notify_one();
 }
 
@@ -270,12 +268,10 @@ void TextureCache::unbindAllImageAsync()
 void TextureCache::loadImage()
 {
     AsyncStruct *asyncStruct = nullptr;
-    std::mutex signalMutex;
-    std::unique_lock<std::mutex> signal(signalMutex);
     while (!_needQuit)
     {
+        std::unique_lock<std::mutex> ul(_requestMutex);
         // pop an AsyncStruct from request queue
-        _requestMutex.lock();
         if (_requestQueue.empty())
         {
             asyncStruct = nullptr;
@@ -285,12 +281,15 @@ void TextureCache::loadImage()
             asyncStruct = _requestQueue.front();
             _requestQueue.pop_front();
         }
-        _requestMutex.unlock();
 
         if (nullptr == asyncStruct) {
-            _sleepCondition.wait(signal);
+            if (_needQuit) {
+                break;
+            }
+            _sleepCondition.wait(ul);
             continue;
         }
+        ul.unlock();
 
         // load image
         asyncStruct->loadSuccess = asyncStruct->image.initWithImageFileThreadSafe(asyncStruct->filename);
@@ -660,8 +659,10 @@ std::string TextureCache::getTextureFilePath(cocos2d::Texture2D* texture) const
 void TextureCache::waitForQuit()
 {
     // notify sub thread to quick
+    std::unique_lock<std::mutex> ul(_requestMutex);
     _needQuit = true;
     _sleepCondition.notify_one();
+    ul.unlock();
     if (_loadingThread) _loadingThread->join();
 }