Cocos2d-x Multithreading sceanrio crashes the game - multithreading

Question

my scenario is simple:i made a game using cocos2d-x and i want to download images (FB and Google play) for multi player users and show them once the download is done as texture for a button.
in ideal world, things work as expected.
things get tricky when those buttons got deleted before the download is done.
so the callback function is in weird state and then i get signal 11 (SIGSEGV), code 1 (SEGV_MAPERR)
and the app crashes
This is how i implmented it
I have a Layout class called PlayerIcon. the cpp looks like this
void PlayerIcon::setPlayer(string userName, string displayName, string avatarUrl){
try {
//some code here
downloadAvatar(_userName, _avatarUrl);
//some code here
}
catch(... ){
}
}
void PlayerIcon::downloadAvatar(std::string _avatarFilePath,std::string url) {
if(!isFileExist(_avatarFilePath)) {
try {
auto downloader = new Downloader();
downloader->onFileTaskSuccess=CC_CALLBACK_1(PlayerIcon::on_download_success,this);
downloader->onTaskError=[&](const network::DownloadTask& task,int errorCode,
int errorCodeInternal,
const std::string& errorStr){
log("error while saving image");
};
downloader->createDownloadFileTask(url,_avatarFilePath,_avatarFilePath);
}
catch (exception e)
{
log("error while saving image: test");
}
} else {
//set texture for button
}
}
void PlayerIcon::on_download_success(const network::DownloadTask& task){
_isDownloading = false;
Director::getInstance()->getScheduler()-> performFunctionInCocosThread(CC_CALLBACK_0(PlayerIcon::reload_avatar,this));
}
void PlayerIcon::reload_avatar(){
try {
// setting texture in UI thread
}
catch (...) {
log("error updating avatar");
}
}
As i said, things works fine until PlayerIcon is deleted before the download is done.
i dont know what happens when the call back of the download task point to a method of un object that s deleted (or flagged for deletion).
i looked in the downloader implementation and it doesn't provide any cancellation mechanism
and i'm not sure how to handle this
Also, is it normal to have 10% crash rate on google console for a cocos2dx game
any help is really appreciated

Answer 1

Do you delete de Downloader in de destructor of the PlayerIcon?
there is a destroy in the apple implementation witch is trigered by the destructor.
-(void)doDestroy
{
// cancel all download task
NSEnumerator * enumeratorKey = [self.taskDict keyEnumerator];
for (NSURLSessionDownloadTask *task in enumeratorKey)
{
....
DownloaderApple::~DownloaderApple()
{
DeclareDownloaderImplVar;
[impl doDestroy];
DLLOG("Destruct DownloaderApple %p", this);
}

Answer 2

In the demo code of cocos2d-x: DownloaderTest.cpp they use:
std::unique_ptr<network::Downloader> downloader;
downloader.reset(new cocos2d::network::Downloader());
instead of:
auto downloader = new Downloader();

Answer 3

It looks like you are building this network code as part of your scene tree. If you do a replaceScene/popScene...() call, while the async network software is running in the background, this will cause the callback to disappear (the scene will be deleted from the scene-stack) and you will get a SEGFAULT from this.
If this is the way you've coded it, then you might want to extract the network code to a global object (singleton) where you queue the requests and then grab them off the internet saving the results in the global-object's output queue (or their name and location) and then let the scene code check to see if the avatar has been received yet by inquiring on the global-object and loading the avatar sprite at this point.
Note, this may be an intermittent problem which depends on the speed of your machine and the network so it may not be triggered consistently.
Another solution ...
Or you could just set your function pointers to nullptr in your PlayerIcon::~PlayerIcon() (destructor):
downloader->setOnFileTaskSuccess(nullptr);
downloader->setOnTaskProgress(nullptr);
Then there will be no attempt to call your callback functions and the SEGFAULT will be avoided (Hopefully).