[Discuss-gnuradio] How the valve block works

[Patrick Strasser]

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Hello!

I'm trying to implement an application with GNU Radio Companion that
incorporates different branches. For example I have a Wav source and a
signal source and I want to switch between them. Or I want to hear the
signal at socertain points in the flow graph. The old way was to use a
variable chooser, const multipliers for muting of paths and adders. The
downside of this system is that all the paths continue to run
concurrently. I do not use the muted paths, but they still consume
processing power.

Now I found the valve block, and the doc says: Connect output to input
when valve is closed (not open).
I expected the valve to block when input is not connected to output. I
thougth the flow graph would starve/block on that path. In consequence
the path would not consume processing power. Now it seems - referring to
Josh's message from 2010-05-06 [1] - that down the path from the valve
indeed starving happens, but the null sink in the valve happily
consumes, keeping the producers running.

I thought about replacing the null sink with something blocking. This
would for sure work with otherwise unconnected sources, like when
choosing between different sources. But I'm not sure what happens if the
path splits before the valve. Would the blocking be propagated back over
the split or be limited to the path with the valve?

Maybe I'm just on the wrong track and there is some other simple
solution for this problem.

Regards

Patrick

[1] http://article.gmane.org/gmane.comp.gnu.radio.general/26777
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