TPL DataFlow 无法处理 ActionBlock 中的异常

Question

我正在尝试将来自ActionBlock<int> 的一条消息的副本发送给多个同样是ActionBlock<int> 的消费者。这很好用，但是如果目标块之一引发异常，似乎这不会传播到源块。这是我尝试处理异常的方法，但它永远不会进入catch 部分：

static void Main(string[] args)
{
    var t1 = new ActionBlock<int>(async i =>
    {
        await Task.Delay(2000);
        Trace.TraceInformation($"target 1 | Thread {System.Threading.Thread.CurrentThread.ManagedThreadId} | message {i}");
    }, new ExecutionDataflowBlockOptions { BoundedCapacity = 5 });

    var t2 = new ActionBlock<int>(async i =>
    {
        await Task.Delay(1000);
        Trace.TraceInformation($"target 2 | Thread {System.Threading.Thread.CurrentThread.ManagedThreadId} | message {i}");
    }, new ExecutionDataflowBlockOptions { BoundedCapacity = 5 });

    var t3 = new ActionBlock<int>(async i =>
    {
        await Task.Delay(100);
        Trace.TraceInformation($"target 3 | Thread {System.Threading.Thread.CurrentThread.ManagedThreadId} | message {i}");
        if (i > 5)
            throw new Exception("Too big number");
    }, new ExecutionDataflowBlockOptions { BoundedCapacity = 5 });

    var targets = new [] { t1, t2, t3};

    var broadcaster = new ActionBlock<int>(
        async item =>
        {
            var processingTasks = targets.Select(async t =>
            {
                try
                {
                    await t.SendAsync(item);
                }
                catch
                {
                    Trace.TraceInformation("handled in select"); // never goes here
                }
            });

            try
            {
                await Task.WhenAll(processingTasks);
            }
            catch
            {
                Trace.TraceInformation("handled"); // never goes here
            }
        });

    for (var i = 1; i <= 10; i++)
        broadcaster.Post(i);
}

我不确定我在这里遗漏了什么，但我希望能够检索异常以及哪个目标块出现故障。

Answer 1

如果一个块进入故障状态，它将不再接受新项目，并且它抛出的Exception 将附加到其Completion 任务和/或如果在管道中链接，则随着其完成传播。要观察Exception，如果块拒绝更多项目，您可以await 完成。

var processingTasks = targets.Select(async t =>
{
    try
    {
        if(!await t.SendAsync(item))
            await t.Completion;
    }
    catch
    {
        Trace.TraceInformation("handled in select"); // never goes here
    }
});