TPL Dataflow, guarantee completion only when ALL source data blocks completed

Question

How can I re-write the code that the code completes when BOTH transformblocks completed? I thought completion means that it is marked complete AND the \" out queue\" is empt

Answer 1

The issue is exactly what casperOne said in his answer. Once the first transform block completes, the processor block goes into “finishing mode”: it will process remaining items in its input queue, but it won't accept any new items.

There is a simpler fix than splitting your processor block in two though: don't set PropagateCompletion, but instead set completion of the processor block manually when both transform blocks complete:

Task.WhenAll(transformBlock1.Completion, transformBlock2.Completion)
    .ContinueWith(_ => processorBlock.Complete());