gistfile1.txt

    public class AsyncCompletion
    {
        /// <summary>
        /// 跟着实例走的默认未完成源
        /// </summary>
        Lazy<TaskCompletionSource<Unit>> _lazyIncompletByDefaultSource =
            new Lazy<TaskCompletionSource<Unit>>(() => new TaskCompletionSource<Unit>(), true);

        /// <summary>
        /// 静态完成源
        /// </summary>
        static Lazy<TaskCompletionSource<Unit>> CompletedSource =
             new Lazy<TaskCompletionSource<Unit>>(() =>
             {
                 var completedSource = new TaskCompletionSource<Unit>();
                 completedSource.SetResult(Unit.Default);
                 return completedSource;
             }, true);

        public Task Completion
        {
            get
            {
                return _lazyIncompletByDefaultSource.Value.Task;
            }

        }

        public void Complete()
        {
            //标记完成
            //   var oldOne = Interlocked.Exchange(ref _lazyIncompletByDefaultSource, CompletedSource); 可以加锁的替换
            var oldOne = _lazyIncompletByDefaultSource;
            _lazyIncompletByDefaultSource = CompletedSource;           
     
            if (oldOne != CompletedSource)
            {
                var cts = _lazyIncompletByDefaultSource.Value;
                cts.TrySetResult(Unit.Default);
            }


        }
    }