AsyncLock

AsyncLock.cs

using System;
using System.Threading;
using System.Threading.Tasks;

/// <summary>
/// A simple FIFO async lock. It does not support recursion/reentrancy.
/// </summary>
public sealed class AsyncLock
{
	private Task task = Task.CompletedTask;

	public async ValueTask LockAsync(Func<Task> whenLocked, CancellationToken cancellationToken = default)
	{
		ArgumentNullException.ThrowIfNull(whenLocked);

		var next = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
		var prev = Interlocked.Exchange(ref task, next.Task);

		try
		{
			await prev.WaitAsync(cancellationToken).ConfigureAwait(false);
		}
		catch (OperationCanceledException)
		{
			_ = prev.ContinueWith(_ => next.SetResult(), TaskContinuationOptions.ExecuteSynchronously);
			throw;
		}

		try
		{
			await whenLocked().ConfigureAwait(false);
		}
		finally
		{
			next.SetResult();
		}
	}
}