UpdateHandle - Investigate supporting async/await

[mbaker3]

Investigate whether supporting the ability to await on update events and intervals/timeouts is performant and feasible.

Desired API

private async void MyMethod()
{
   await m_UpdateHandle.CallAfter(1.5f, UpdateHandle.FixedDeltaProvider);
   await m_UpdateHandle.CallAfterUpdates(1);
   await m_UpdateHandle.OnUpdateAwaiter;
}

Questions

• Does this approach perform similarly to the existing callback/event based API?
• Do async methods resume execution on their own thread or on the thread of their await target?
  • We need the methods to resume on the same thread that the update handle calls on. Many applications use update handles to marshal calls back onto their main thread.

TaskCompletionSource vs SemaphoreSlim

Which is lighter weight and the better way to go?

TaskCompletionSource

private Task WaitOnUpdate()
{
    //TODO: Substitute for non-generic in .NET5 - https://github.com/dotnet/runtime/pull/37452
    TaskCompletionSource<bool> completionSource = new TaskCompletionSource<bool>();
    updateHandle.OnUpdate += () =>
    {
        completionSource.TrySetResult(true);
    };

    return completionSource.Task;
}

SemaphoreSlim

private Task WaitOnUpdate()
{
    SemaphoreSlim semaphore = new SemaphoreSlim(0, 1);
    updateHandle.OnUpdate += () =>
    {
        semaphore.Release();
    };

    return semaphore.WaitAsync();
}