Just some crazy POC for dispatchers

DispatcherSandbox.cs

/*

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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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SOFTWARE.

*/

// Portions inspired by 
// https://github.com/i3arnon/AsyncUtilities/tree/c185cc4a1a859049112b18065c0c772593c786e7/src/AsyncUtilities/TaskEnumerableAwaiter

using System.Runtime.CompilerServices;
using System.Threading.Channels;
using System.Threading.Tasks.Sources;

namespace JFA.Dispatchers;

public abstract class DispatcherItem : ICriticalNotifyCompletion
{
    public abstract bool IsCompleted { get; }
    public abstract ValueTask Run();

    public static ReturnFuncBasedDispatcher<T> Create<T>(Func<Task<T>> action)
    {
        return new ReturnFuncBasedDispatcher<T>(action);
    }

    public static NoReturnFuncBasedDispatcherBase Create(Func<Task> action)
    {
        return new NoReturnFuncBasedDispatcher(action);
    }

    public static NoReturnFuncBasedDispatcherBase Create<TState>(TState state, Func<TState, Task> action)
    {
        return new StateHoldingNoReturnFuncBasedDispatcher<TState>(state, action);
    }

    public abstract void OnCompleted(Action continuation);
    public abstract void UnsafeOnCompleted(Action continuation);
    public abstract void TrySetError(Exception exception);

    public static ReturnFuncBasedDispatcherBase<TResult> Create<TResult, TState>(TState action,
        Func<TState, Task<TResult>> func)
    {
        return new StateHoldingReturnFuncBasedDispatcher<TState, TResult>(action, func);
    }
}

public readonly struct ConfiguredTaskNoReturnAwaitable<TResult>
{
    internal readonly NoReturnFuncBasedDispatcherBase _item;

    /// <summary>Initializes the awaitable.</summary>
    /// <param name="tasks">The tasks to be awaited.</param>
    /// <param name="continueOnCapturedContext">
    /// true to attempt to marshal the continuation back to the original synchronization context captured; otherwise, false.
    /// </param>
    internal ConfiguredTaskNoReturnAwaitable(NoReturnFuncBasedDispatcherBase item)
    {
        _item = item;
    }

    /// <summary>Returns an awaiter for this <see cref="ConfiguredTaskNoReturnAwaitable{TResult}"/> instance.</summary>
    public NoReturnFuncBasedDispatcherBase GetAwaiter() =>
        _item;

}

public readonly struct ConfiguredTaskReturnAwaitable<TResult>
{
    internal readonly ReturnFuncBasedDispatcherBase<TResult> _item;

    /// <summary>Initializes the awaitable.</summary>
    /// <param name="tasks">The tasks to be awaited.</param>
    /// <param name="continueOnCapturedContext">
    /// true to attempt to marshal the continuation back to the original synchronization context captured; otherwise, false.
    /// </param>
    internal ConfiguredTaskReturnAwaitable(ReturnFuncBasedDispatcherBase<TResult> item)
    {
        _item = item;
    }

    /// <summary>Returns an awaiter for this <see cref="ConfiguredTaskNoReturnAwaitable{TResult}"/> instance.</summary>
    public ReturnFuncBasedDispatcherBase<TResult> GetAwaiter() =>
        _item;

}

public abstract class NoReturnFuncBasedDispatcherBase : DispatcherItem, ICriticalNotifyCompletion
{
    protected ManualResetValueTaskSourceCore<int> _mrvtcs;
    public override bool IsCompleted => _mrvtcs.GetStatus(_mrvtcs.Version) != ValueTaskSourceStatus.Pending;

    public NoReturnFuncBasedDispatcherBase(bool noAsync = false)
    {
        _mrvtcs = new ManualResetValueTaskSourceCore<int>();
        _mrvtcs.RunContinuationsAsynchronously = !noAsync;
    }

    public override void OnCompleted(Action continuation)
    {
        _mrvtcs.OnCompleted(static o => ((Action)o!)(), continuation, _mrvtcs.Version,
            ValueTaskSourceOnCompletedFlags.None);
    }

    public override void UnsafeOnCompleted(Action continuation)
    {
        _mrvtcs.OnCompleted(static o => ((Action)o!)(), continuation, _mrvtcs.Version,
            ValueTaskSourceOnCompletedFlags.None);
    }

    public override void TrySetError(Exception exception)
    {
        _mrvtcs.SetException(exception);
    }

    public void SetCanceled(Exception ex = null)
    {
        _mrvtcs.SetException(new TaskCanceledException("The dispatcher was closed", ex));
    }

    public object GetResult()
    {
        return default;
    }
}

public class NoReturnFuncBasedDispatcher : NoReturnFuncBasedDispatcherBase, ICriticalNotifyCompletion
{
    private readonly Func<Task> _toRun;
    public override bool IsCompleted => _mrvtcs.GetStatus(_mrvtcs.Version) != ValueTaskSourceStatus.Pending;

    public NoReturnFuncBasedDispatcher(Func<Task> toRun, bool noAsync = false)
    {
        _toRun = toRun;
        _mrvtcs = new ManualResetValueTaskSourceCore<int>();
        _mrvtcs.RunContinuationsAsynchronously = true;
    }

    public sealed override async ValueTask Run()
    {
        try
        {
            await _toRun();
            _mrvtcs.SetResult(0);
        }
        catch (Exception e)
        {
            _mrvtcs.SetException(e);
        }
    }
}

public class StateHoldingNoReturnFuncBasedDispatcher<TState> : NoReturnFuncBasedDispatcherBase,
    ICriticalNotifyCompletion
{
    private readonly Func<TState, Task> _toRun;
    private readonly TState _state;
    public override bool IsCompleted => _mrvtcs.GetStatus(_mrvtcs.Version) != ValueTaskSourceStatus.Pending;

    public StateHoldingNoReturnFuncBasedDispatcher(TState state, Func<TState, Task> toRun, bool noAsync = false)
    {
        _state = state;
        _toRun = toRun;
        _mrvtcs = new ManualResetValueTaskSourceCore<int>();
        _mrvtcs.RunContinuationsAsynchronously = true;
    }

    public sealed override async ValueTask Run()
    {
        try
        {
            await _toRun(_state);
            _mrvtcs.SetResult(0);
        }
        catch (Exception e)
        {
            _mrvtcs.SetException(e);
        }
    }

}

public abstract class ReturnFuncBasedDispatcherBase<TResult> : DispatcherItem, ICriticalNotifyCompletion
{
    protected ManualResetValueTaskSourceCore<TResult> _mrvtcs;

    protected ReturnFuncBasedDispatcherBase(bool noAsync)
    {
        _mrvtcs = new ManualResetValueTaskSourceCore<TResult>();
        _mrvtcs.RunContinuationsAsynchronously = !noAsync;
    }

    public override void OnCompleted(Action continuation)
    {
        _mrvtcs.OnCompleted(static o => ((Action)o!)(), continuation, _mrvtcs.Version,
            ValueTaskSourceOnCompletedFlags.None);
    }

    public override void UnsafeOnCompleted(Action continuation)
    {
        _mrvtcs.OnCompleted(static o => ((Action)o!)(), continuation, _mrvtcs.Version,
            ValueTaskSourceOnCompletedFlags.None);
    }

    public override void TrySetError(Exception exception)
    {
        _mrvtcs.SetException(exception);
    }

    public TResult GetResult()
    {
        return (TResult)(object)_mrvtcs.GetResult(_mrvtcs.Version)!;
    }

    public void SetCanceled(Exception ex = null)
    {
        _mrvtcs.SetException(new TaskCanceledException("The dispatcher was closed", ex));
    }
}

public class ReturnFuncBasedDispatcher<TResult> : ReturnFuncBasedDispatcherBase<TResult>, ICriticalNotifyCompletion
{
    private readonly Func<Task<TResult>> _toRun;

    public override bool IsCompleted => _mrvtcs.GetStatus(_mrvtcs.Version) != ValueTaskSourceStatus.Pending;

    public ReturnFuncBasedDispatcher(Func<Task<TResult>> toRun, bool noAsync = false) : base(noAsync)
    {
        _toRun = toRun;
        _mrvtcs = new ManualResetValueTaskSourceCore<TResult>();
    }

    public sealed override async ValueTask Run()
    {
        try
        {
            _mrvtcs.SetResult(await _toRun());
        }
        catch (Exception e)
        {
            _mrvtcs.SetException(e);
        }
    }

}

public class StateHoldingReturnFuncBasedDispatcher<TState, TResult> : ReturnFuncBasedDispatcherBase<TResult>,
    ICriticalNotifyCompletion
{
    private readonly Func<TState, Task<TResult>> _toRun;

    private readonly TState _state;

    public override bool IsCompleted => _mrvtcs.GetStatus(_mrvtcs.Version) != ValueTaskSourceStatus.Pending;

    public StateHoldingReturnFuncBasedDispatcher(TState state, Func<TState, Task<TResult>> toRun,
        bool noAsync = false) : base(noAsync)
    {
        _state = state;
        _toRun = toRun;
    }

    public sealed override async ValueTask Run()
    {
        try
        {
            _mrvtcs.SetResult(await _toRun(_state));
        }
        catch (Exception e)
        {
            _mrvtcs.SetException(e);
        }
    }

    public override void TrySetError(Exception exception)
    {
        _mrvtcs.SetException(exception);
    }

}

public class AsyncChannelDispatcher
{
    public readonly Channel<DispatcherItem> _ch = Channel.CreateUnbounded<DispatcherItem>();
    private readonly Task _taskSet;

    public AsyncChannelDispatcher(int maxThreads, bool configureAwaitFalse = false)
    {
        var caw = !configureAwaitFalse;
        var taskArr = new Task[maxThreads];
        for (int i = 0; i < maxThreads; i++)
        {
            taskArr[i] = Task.Run(async () =>
            {
                try
                {
                    while (await _ch.Reader.WaitToReadAsync())
                    {
                        while (_ch.Reader.TryRead(out var item))
                        {
                            try
                            {
                                await item.Run().ConfigureAwait(caw);
                            }

                            catch (Exception e)
                            {
                                item.TrySetError(e);
                            }
                        }
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    throw;
                }

                return 0;
            });
        }

        _taskSet = Task.WhenAll(taskArr);
    }

    public async Task ScheduleAction(Func<Task> action)
    {
        var item = DispatcherItem.Create(action);
        if (!_ch.Writer.TryWrite(item))
        {
            item.SetCanceled();
        }

        await new ConfiguredTaskNoReturnAwaitable<object>(item);
    }

    public async Task ScheduleAction<TState>(TState state, Func<TState, Task> action)
    {
        var item = DispatcherItem.Create<TState>(state, action);
        if (!_ch.Writer.TryWrite(item))
        {
            item.SetCanceled();
        }

        await new ConfiguredTaskNoReturnAwaitable<object>(item);
    }

    public async Task<TResult> ScheduleAction<TResult>(Func<Task<TResult>> action)
    {
        var item = DispatcherItem.Create(action);
        if (!_ch.Writer.TryWrite(item))
        {
            item.SetCanceled();
        }

        return await new ConfiguredTaskReturnAwaitable<TResult>(item);
    }

    public async Task<TResult> ScheduleAction<TState, TResult>(TState state, Func<TState, Task<TResult>> action)
    {
        var item = DispatcherItem.Create(state, action);
        if (!_ch.Writer.TryWrite(item))
        {
            item.SetCanceled();
        }

        return await new ConfiguredTaskReturnAwaitable<TResult>(item);
    }
}