TPL.Dataflow message processing timeout?

Question

Using .NET TPL DataFlow blocks. Is there any way to timeout the processing of a message?

e.g.

lets say I have a BufferBlock<T>, is it possible to link that to another block that processes one message at a time (MaxDegreeOfParallellism 1) and force a timeout if the processing runs for too long? Or is it even possible to do using the BufferBlock only?

I suspect I can use a cancellation token somehow and a delay, but not sure how this would be done. Also, how expensive would such timeout be? would it add much overhead to the message processing time?

Answer 1

Many methods of BufferBlock<T> do accept CancellationToken, and I believe that would be the proper way of timing out an operation. E.g.:

var cts = new CancellationTokenSource(5000); // cancel in 5s 
// Alternatively: cts.CancelAfter(5000);

try 
{
    var output = await bufferBlock.ReceiveAsync(cts.Token);
}
catch (Exception ex)
{
    // check if ex is OperationCanceledException,
    // which could be wrapped with AggregateException 
}

IMO, the only way of evaluating its efficiency would be to run some profiling tests.

[UPDATE] Based upon the comments, if you're looking to time-out the pipeline processing, you can probably do that when you construct your ActionBlock object and provide it with an instance of ExecutionDataflowBlockOptions. At that point, you can supply DataflowBlockOptions.CancellationToken and use it in the same way as described above. Also, you could pass a CancellationToken into LinkTo as a part of DataflowLinkOptions.

Once you've provided the pipeline with a CancellationToken, you can track the status of ActionBlock.Completion/TransformBlock.Completion, which is a Task, so you can await it and catch a cancellation exception, or use ContinueWith with it (if that's what you mean under some way to tell if the "processing" of the message times out).

Disclaimer: I haven't tried this myself and would be interested to know whether it works as expected.