第一个项目等待第二个项目时数据流死锁

Question

我有一个奇怪的死锁问题，简单的数据流 - 转换块和动作块。变换块应等待第一个项目，直到第二个项目进入操作块。基本上我想测试一下，如果一个项目阻塞某些外部资源，那么其他项目应继续流动。但它似乎无法正常工作。

[Fact]
public void ProcessAction_FirstWaitsForTheSecond_DataflowEndedOnlyAfterBothProcessed ()
{
    // arrange
    var second_item_finished = new SemaphoreSlim (0, 1);
    var completed_items = new ConcurrentBag<string> ();

    var starting_block = new TransformBlock<string, string>
        (x =>
            {
                if (x == "1")
                    second_item_finished.Wait ();

                return x;
            },
            new ExecutionDataflowBlockOptions
            {
                BoundedCapacity = 100,
                MaxDegreeOfParallelism = 4
            });

    var ending_block = new ActionBlock<string>
        (x =>
            {
                completed_items.Add (x);

                if (x == "2")
                    second_item_finished.Release ();
            },
            new ExecutionDataflowBlockOptions
            {
                BoundedCapacity = 100,
                MaxDegreeOfParallelism = 4
            });

    starting_block.LinkTo (ending_block, new DataflowLinkOptions { PropagateCompletion = true });


    // act
    foreach (var data in new[] { "1", "2" })
    {
        if (!starting_block.SendAsync (data).Wait (1000))
            throw new TimeoutException ();
    }

    starting_block.Complete ();

    // timeout here
    if (!Task.WaitAll (new[] { starting_block.Completion, ending_block.Completion }, 1000))
        throw new TimeoutException ();


    // assert
    completed_items.Should ().Equal ("2", "1");
}

我在＆＃34; WaitAll＆＃34;线。