Joining on a thread that fires a delegate

Development Programming & Scripting C++
9

I was sure you were wrong about this, but I ran a test:


uint32 AMyActor::Runnable::Run()
{
    uint32 ThreadId = FPlatformTLS::GetCurrentThreadId();
   FString ThreadName = FThreadManager::Get().GetThreadName(ThreadId);
    UE_LOG(LogTemp, Warning, TEXT("background thread name %s"), *ThreadName);
    Delegate.BindLambda(](){
        uint32 ThreadId = FPlatformTLS::GetCurrentThreadId();
       FString ThreadName = FThreadManager::Get().GetThreadName(ThreadId);
        UE_LOG(LogTemp, Warning, TEXT("delegate callback in thread name %s"), *ThreadName);
    });
    Delegate.Execute();
    return 0;
}

A background thread launched on BeginPlay, which binds and fires a delegate in the thread. The output:


[2019.08.26-17.33.31:279][839]LogTemp: Warning: background thread name BgThread
[2019.08.26-17.33.31:279][839]LogTemp: Warning: delegate callback in thread name BgThread

So it appears you’re right…I was assuming that the delegates themselves put themselves on a queue when they Broadcast/Execute, and the Gamethread then runs through that queue and processes the callbacks.

Digging a little deeper though, it looks like the HttpManager ticks on the game thread, which means finishing requests and firing the FHttpRequestCompleteDelegate on the game thread. I guess this is what you meant when you said “explicitly sending the work to the game thread” ? I took that to mean the IO transfer and was thinking “no way, that would lag the game so much” :slight_smile: The IO transfer itself is done in a background thread managed by HttpManager

So I guess the issue I was having isn’t with the delegates themselves, but when the HttpManager decides to fire the delegates, which is on the game thread, causing my deadlock.