Intel TBB input_node output value caching delays resource release. Workaround ideas?

Question

I'm new to the Intel Threading Building Blocks and playing with the flow graph component. So far, its worked mostly well. My messages between nodes are shared_ptr types so they are copy-constructble, lightweight, and the underlying resource is disposed of at the end of a graph cycle...

Except for messages that originate from my input_node. input_node is designed so that it holds a copy of its last output value. This means that the any resource held by the value output by an input_node won't be released until the input_node generates its next output.

This seems awkward/inconsistent with the rest of the API. Any thoughts on how to deal with it? I guess I could write my own node, but I'd rather not. Should I just use try_put? If so, how do I let the graph know when I'm done providing inputs, so that wait_for_all doesn't conclude early?

Answer 1

An easy workaround is to have the input_node generate a message which does not utilize shared_ptr types, and feeds immediately to a function_node whose output does utilize any shared_ptr types you want to propagate and have collected when the propagation is complete. It feels a little silly, but works well. There may be nodes besides input_node that do caching, but I'm using function_node, multifunction_node, and indexer_node without any evidence of the caching that input_node does.

As an aside, it always creeps me out a little bit when I google a problem and end up on one of my own questions on stackoverflow, and it's been long enough that I don't remember posting the question. When I don't see an answer it adds some disappointment to the emotions too. ;-)

At least on this one by the time I came back I had become used enough to TBB dataflow that an easy workaround was readily apparent.