EngineDispatcher.cs

using System.Collections.Concurrent;
 
namespace Gondwana;

public sealed class EngineDispatcher : IEngineDispatcher
{
    private readonly ConcurrentQueue<Action> _queue = new();
    private int _engineThreadId;

    public void BindToCurrentThread() => _engineThreadId = Environment.CurrentManagedThreadId;

    public bool IsOnEngineThread => Environment.CurrentManagedThreadId == _engineThreadId;

    public void Post(Action action)
    {
        if (action is null)
            return;
 
        // run inline if already on engine thread.
        if (IsOnEngineThread)
        {
            action();
            return;
        }
 
        _queue.Enqueue(action);
    }

    public Task PostAsync(Func<Task> action)
    {
        if (action is null)
            return Task.CompletedTask;
 
        var completionSource = new TaskCompletionSource(
            TaskCreationOptions.RunContinuationsAsynchronously);
 
        Post(() => _ = ExecuteAsync());
 
        return completionSource.Task;
 
        async Task ExecuteAsync()
        {
            try
            {
                await action();
                completionSource.SetResult();
            }
            catch (Exception ex)
            {
                completionSource.SetException(ex);
            }
        }
    }

    public void Drain()
    {
        while (_queue.TryDequeue(out var a))
            a();
    }
}