條件匹配時的TPL數據流完成管道

Question

我認為這是一種非常基本的方法，但尚未找到任何示例。 我有一個生產者和一個消費者，我想在處理至少x個對象時完成管道。 另外，我需要知道已接收到哪些對象。

我就是這樣的：

public class BlockTester
{
    private static TransformBlock<int, int> _worker;

    public static async Task StartAsync()
    {
        _worker = new TransformBlock<int, int>(s => s + s);
        var buffer = new BufferBlock<int>();
        var consumeTask = Consume(buffer);

        _worker.LinkTo(buffer, new DataflowLinkOptions{PropagateCompletion = true});

        foreach (var value in Enumerable.Range(0,100))
        {
            _worker.Post(value);
        }

        _worker.Complete();

        await buffer.Completion;

        if(buffer.TryReceiveAll(out var received))
        {
            Console.WriteLine(string.Join(", ", received));
        }
    }

    public static async Task<IReadOnlyCollection<int>> Consume(ISourceBlock<int> buffer)
    {
        var received = new List<int>();

        while (await buffer.OutputAvailableAsync())
        {
            var current = buffer.Receive();

            received.Add(current);

            if (current > 25)
            {
                _worker.Complete();
            }
        }

        return received;
    }
}

我對buffer.TryReceiveAll有點困惑。 等待消耗任務和TryReceiveAll有什么區別？ 為什么在我的情況下TryReceiveAll為假？ 我想我達到目標的方法仍然存在問題。

Answer 1

您的Consume方法應該是ActionBlock 。 無需使用OutputAvailableAsync或TryRecieveAll 。 更換BufferBlock與ActionBlock和內做你的處理ActionBlock 。 除非您在過程中有多個步驟，否則尚不清楚為什么您也需要TransformBlock 。

public class BlockTester
{
    //Could be removed
    private static TransformBlock<int, int> _worker;

    public static async Task StartAsync()
    {
        //Could be removed
        _worker = new TransformBlock<int, int>(s => s + s);
        var processor = new ActionBlock<int>(x => ProcessMessage(x));

        _worker.LinkTo(processor, new DataflowLinkOptions { PropagateCompletion = true });

        foreach (var value in Enumerable.Range(0, 100))
        {
            _worker.Post(value);
        }

        //_worker.Complete();

        await processor.Completion;
    }


    private static int itemsRecieved = 0;
    public static void ProcessMessage(int x)
    {
        Interlocked.Increment(ref itemsRecieved);
        if (itemsRecieved > 25) _worker.Complete();
        //process the message
        //log the message etc.
    }
}

或使用復雜的消息對象：

public class Message { }

public class BlockTester
{
    //Could be removed
    private static TransformBlock<Message, Message> _worker;

    public static async Task StartAsync()
    {
        //Could be removed
        _worker = new TransformBlock<Message, Message>(s => s);
        var processor = new ActionBlock<Message>(x => ProcessMessage(x));

        _worker.LinkTo(processor, new DataflowLinkOptions { PropagateCompletion = true });

        foreach (var value in Enumerable.Range(0, 100).Select(_ => new Message()))
        {
            _worker.Post(value);
        }

        //_worker.Complete();

        await processor.Completion;
    }


    private static ConcurrentBag<Message> itemsRecieved = new ConcurrentBag<Message>();
    public static void ProcessMessage(Message x)
    {
        itemsRecieved.Add(x);
        if (itemsRecieved.Count > 25) _worker.Complete();
        //process the message
        //log the message etc.
    }
}

編輯以回答原始問題：

為什么TryReceiveAll返回false：

因為在運行TryReceiveAll ， BufferBlock已“完成”。 要完成一個塊，它的輸出緩沖區中必須包含0個項目。 Consume方法是在允許該塊完成之前拉出所有項目，最后您將在一個空塊上調用TryRecieveAll 。