How can I drop a message between linked blocks

Question

How can I drop a message between a link. When dropping I don't want to break the link, so that followed messages can be flowed over the link. (It seems that a filter used with LinkTo would break the link.)

Thanks in advance!

Answer 1

LinkTo with a predicate doesn't break the link, but without an alternative some messages may end up blocking the sourceblock.

Consider the following example where we want to print all even numbers in a buffer:

BufferBlock<Int32> buffer = new BufferBlock<Int32>();
ActionBlock<Int32> writer = new ActionBlock<Int32>((n) => Console.WriteLine(n));

foreach (var number in Enumerable.Range(0, 10))
{
    buffer.Post(number);
}

buffer.LinkTo(writer, (i) => i % 2 == 0);
buffer.LinkTo(DataflowBlock.NullTarget<Int32>());

Without a proper fallback (last line, the link to NullTarget) the message containing value 1 will block. So just add a DataflowBlock.NullTarget<T> and that will drop messages for you.

Answer 2

Thanks Lasagna!

I tried. What you anwered works.