Why is the thrown exception not printed in the background thread?

[a13782425]

Why is the thrown exception not printed in the background thread?
Code

private async void RunTest()
{
    Debug.LogError("RunTest:1");
    Debug.LogError("ThreadId:"+Thread.CurrentThread.ManagedThreadId);
    await PromiseYielder.WaitForRealTime(2);
    await Promise.SwitchToBackgroundAwait();
    Debug.LogError("ThreadId:"+Thread.CurrentThread.ManagedThreadId);
    await PromiseYielder.WaitForRealTime(2);
    Debug.LogError("cccc");
    await Promise.SwitchToForegroundAwait();
    Debug.LogError(Thread.CurrentThread.ManagedThreadId);
    Debug.LogError("ttt");
    await PromiseYielder.WaitForRealTime(2);
    Debug.LogError("RunTest:2");
}

[timcassell]

Probably because you're using async void which is using the built-in Tasks system, not ProtoPromise. I'm not entirely sure how it handles uncaught exceptions. Try refactoring to this:

private void RunTest()
{
    Run().Forget();
    
    async Promise Run()
    {
        Debug.LogError("RunTest:1");
        Debug.LogError("ThreadId:"+Thread.CurrentThread.ManagedThreadId);
        await PromiseYielder.WaitForRealTime(2);
        await Promise.SwitchToBackgroundAwait();
        Debug.LogError("ThreadId:"+Thread.CurrentThread.ManagedThreadId);
        await PromiseYielder.WaitForRealTime(2);
        Debug.LogError("cccc");
        await Promise.SwitchToForegroundAwait();
        Debug.LogError(Thread.CurrentThread.ManagedThreadId);
        Debug.LogError("ttt");
        await PromiseYielder.WaitForRealTime(2);
        Debug.LogError("RunTest:2");
    }
}

[a13782425]

Thanks, this does get exceptions, why can't get exceptions using async void which is using the built-in Tasks system?

[timcassell]

I'm guessing it has to do with the issue described in this forum thread: https://forum.unity.com/threads/suppressing-not-logging-exceptions-from-threadpool-and-async-void-methods-from-non-main-thread.1059491/

[a13782425]

This is a difficult question.

[timcassell]

See also #137 (comment)

[a13782425]

Except for Run().Forget();, Does it have a blocking version? Similar toRun().GetAwaiter().GetResult();, but calling it throws an exception

[timcassell]

You can use .Wait(). Be careful, though, as you may deadlock if the operation tries to switch to the same thread.