TPL数据流无法处理ActionBlock中的异常

我正试图从一个 ActionBlock<int> 对于多个消费者 . 这很好,但是如果其中一个目标块引发异常,则这似乎不会传播到源块。在这里,我试图处理异常,但它从未转到 catch

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。