2019-12-1-实现一种异步版本的ManualResetEvent

    public class ManualResetEventAsync
    {
        /// <summary>
        /// 提供一个信号初始值，确定是否有信号
        /// </summary>
        /// <param name="initialState">true为有信号，所有等待可以直接通过</param>
        public ManualResetEventAsync(bool initialState)
        {
            _source = new TaskCompletionSource<bool>();

            if (initialState)
            {
                _source.SetResult(true);
            }
        }

        /// <summary>
        /// 异步等待一个信号，需要await
        /// </summary>
        /// <returns></returns>
        public Task WaitOneAsync()
        {
            lock (_locker)
            {
                return _source.Task;
            }
        }

        /// <summary>
        /// 设置一个信号量，所有等待获得信号
        /// </summary>
        public void Set()
        {
            lock (_locker)
            {
                _source.SetResult(true);
            }
        }

        /// <summary>
        /// 设置一个信号量，所有wait等待
        /// </summary>
        public void Reset()
        {
            lock (_locker)
            {
                if (!_source.Task.IsCompleted)
                {
                    return;
                }

                _source = new TaskCompletionSource<bool>();
            }
        }

        private TaskCompletionSource<bool> _source;
        private readonly object _locker = new object();
    }