AsyncLock

AsyncLock.cs

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

namespace AsyncLockExtensions
{
    /// <summary>
    /// Virtual critical section for async function.
    /// Monitor.Enter/Exit and lock{} does not work for async methods and cause deadlocks and exceptions. AsyncLock solves these issues. Implementation copied from Microsoft.EntityFrameworkCore.Internal.AsyncLock (.nuget\packages\microsoft.entityframeworkcore\2.1.4\lib\netstandard2.0\Microsoft.EntityFrameworkCore.dll)
    /// <seealso cref="https://github.com/neosmart/AsyncLock"/>
    /// <example>
    /// using(await _myLock.LockAsync())
    /// {
    ///     //critical section code
    /// }
    /// </example>
    /// </summary>
    public class AsyncLock
    {
        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1);
        private readonly AsyncLock.Releaser _releaser;
        private readonly Task<AsyncLock.Releaser> _releaserTask;

        public AsyncLock()
        {
            this._releaser = new AsyncLock.Releaser(this);
            this._releaserTask = Task.FromResult<AsyncLock.Releaser>(this._releaser);
        }

        public Task<AsyncLock.Releaser> LockAsync(CancellationToken cancellationToken = default(CancellationToken))
        {
            Task task = this._semaphore.WaitAsync(cancellationToken);
            if (!task.IsCompleted)
                return task.ContinueWith<AsyncLock.Releaser>((Func<Task, object, AsyncLock.Releaser>)((_, state) => ((AsyncLock)state)._releaser), (object)this, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
            return this._releaserTask;
        }

        public AsyncLock.Releaser Lock()
        {
            this._semaphore.Wait();
            return this._releaser;
        }

        public struct Releaser : IDisposable
        {
            private readonly AsyncLock _toRelease;

            internal Releaser(AsyncLock toRelease)
            {
                this._toRelease = toRelease;
            }

            public void Dispose()
            {
                this._toRelease._semaphore.Release();
            }
        }
    }
}