Callback of request is never called when I put std::this_thread::sleep_for(1) - c++

Question

I am trying to prevent entering in scene if some stuff from server are not loaded, I have flag bool
done = false;
CCHttpRequest *pRequest;
// initialization ....
pRequest->setResponseCallback(this, httpresponse_selector(SceneController::on_response));
CCHttpClient::getInstance()->send(pRequest);
pRequest->release();
while(!done) {
std::chrono::milliseconds duration(1);
std::this_thread::sleep_for(duration);
}
in function callback on_response I set
done = true;
what should ( but doesn't work ) break out of infinite loop.
Problem with this approach is that callback is never called ( breakpoint at the first line in callback is never reached ). When I comment while loop it called callback.
Does anyone know what is a problem and how to prevent further execution until I fetch data from server ?
Callstack when it works on break point inside callback

Answer 1

Callback is NOT another thread as you might be thinking. You trying hold current function execution 'till callback gets called'. That's not correct. You should return from it and allow callback to be called. This should do:
done = false;
CCHttpRequest *pRequest;
// initialization ....
pRequest->setResponseCallback(this, httpresponse_selector(SceneController::on_response));
CCHttpClient::getInstance()->send(pRequest);
pRequest->release();
if (!done)
{
return;
}
else
{
// Do here whatever you want to do after callback changes flag
}

Answer 2

All your code would be executed in Cocos thread, CCHttpRequest has its own thread to fetch data from server then when all data was fetched the callback you registered before would be called in cocos thread, too.
After the registration of callback, cocos thread continues to execute to your while, now the callback is not called (data isn't completed) your while will run forever. When the data is completed, callback need to be executed in cocos thread but you're seeing the while keep blocking it.
In async world (see here, and here, you must understand async), you cannot "prevent further execution until you fetch data from server" with the pattern you are using. Try to prevent it by your done variable in places that you want it does not be executed.
E.g:
done = false;
CCHttpRequest *pRequest;
// initialization ....
pRequest->setResponseCallback(this, httpresponse_selector(SceneController::on_response));
CCHttpClient::getInstance()->send(pRequest);
pRequest->release();
and then in any you don't want user to interact with your game interface, as in Touch:
void onTouchBegan(Event *pEvent, Touch *pTouch)
{
if (!done)
{
return false;
}
// code when `done == true`
}
void onTouchEnded(Event *pEvent, Touch *pTouch)
{
// Code here will not be executed if `onTouchBegan` return `false`
}
whenever onTouchBegan return false, no more of touch code will be executed then prevent your user from interacting with game's element.
Also to prevent buttons menu clicking, set disable to their parent Menu container: menu->setEnabled(false) then set back to enabled when fetching done.