*Fix: GLThread and other threads access sDownloaderMap in a thread-un…

[pwang08]

GLThread and other threads(js_load_remote_image creates CCDownloader in another thread) access sDownloaderMap in a thread-unsafe way, which will result in crash in some occasion on Android.

[dumganhar]

Hi, pwang08,
I notice that Downloader instance is usually constructed in GL thread.
And the callback functions are also invoked from GL thread. Could this cause thread problems?

Cocos2dxHelper.runOnGLThread(new Runnable() {
            @Override
            public void run() {
                nativeOnProgress(_id, id, downloadBytes, downloadNow, downloadTotal);
            }
        });

[pwang08]

void __JSDownloaderDelegator::downloadAsync() { retain(); auto t = std::thread(&__JSDownloaderDelegator::startDownload, this); t.detach(); }

As the code above shows: __JSDownloaderDelegator::startDownload is called in another thread, in which a Downloader instance is created. As the code below shows:

void __JSDownloaderDelegator::startDownload() { if (auto texture = Director::getInstance()->getTextureCache()->getTextureForKey(_url)) { onSuccess(texture); } else { _downloader = std::make_shared<cocos2d::network::Downloader>(); } }

[dumganhar]

@pwang08 , it makes sense.

@pandamicro , Could you please check it since if I remember correctly, __JSDownloaderDelegator stuff was written by u.

[pandamicro]

Yes, it was originally created by me, at the time, there was a performFunctionInCocosThread to ensure everything is thread safe. But @yangws have refactored the network module and removed these code because network it self will make sure callbacks are invoked in cocos thread.

[minggo]

just close/reopen it to trigger ci. This PR seems good.