How do I link multiple target blocks with a source block in TPL Dataflow?

Question

I expected the following to produce output from both publishers, but it only produces output from the first one:

var broadcastBlock = new BroadcastBlock<int>(null);
var transformBlock = new TransformBlock<int, int>(i => i*10);
var publish1 = new ActionBlock<int>(i => Console.WriteLine("Publisher 1:" + i));
var publish2 = new ActionBlock<int>(i => Console.WriteLine("Publisher 2:" + i));

broadcastBlock.LinkTo(transformBlock, new DataflowLinkOptions() { PropagateCompletion = true });
transformBlock.LinkTo(publish1, new DataflowLinkOptions() { PropagateCompletion = true });
transformBlock.LinkTo(publish2, new DataflowLinkOptions() { PropagateCompletion = true });

foreach (var i in Enumerable.Range(0, 5))
{
    broadcastBlock.Post(i);
}
broadcastBlock.Complete();
Task.WhenAll(publish1.Completion, publish2.Completion).Wait();

I'm obviously missing something fundamental here, any ideas?

Answer 1

You are linking 2 ActionBlocks to a single TransformBlock. You should be linking the 2 ActionBlocks to the BrodcastBlock and link the BroadcastBlock to the TransformBlock.

What you have:

BroadCast => Transfrom => ActionBlock
                       => ActionBlock

What you need:

Transfrom => BroadCast => ActionBlock
                       => ActionBlock