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Re: [Discuss-gnuradio] Two instances of the same custom block walk into

From: Albin Stigö
Subject: Re: [Discuss-gnuradio] Two instances of the same custom block walk into a bar
Date: Thu, 9 May 2019 20:54:00 +0200

Every instance of a block is an instance of the c++ class but like Nick says all your variables are static and not member variables. Those need to be declared in the header. Your two block instances are referring to the same variables and that's why things get messed up.

"A tour of C++" by Bjarne Stroustrup is a good refresher on C++.


On Thu, May 9, 2019, 20:46 Nick Foster <address@hidden> wrote:
It looks like you've declared a bunch of static variables within your block's namespace. Those variables (including pointers!) will be shared with every instance of your block. This is Bad News. Those variables should probably all be declared in the header as class member variables.

On Thu, May 9, 2019 at 11:43 AM Brad Hein <address@hidden> wrote:
I'm running into a strange issue with a new flow graph [1] I'm working on that uses a custom C++ block [2] that I built. The block takes input samples, performs some DSP, and outputs modified samples at the same sample rate.

When the flowgraph has a single instance of my custom block enabled, it works fine. But when I enable a second instance of the block in a separate second usage, (think stereo sound, one per sink channel) it acts very unexpectedly - output samples are wildly inaccurate and distorted.

My perception is that the two instances of the same block seem to be sharing some part of their memory namespace and as they modify/store variables they are doing so in some sort of shared namespace or memory segment.

Is it possible for two blocks to corrupt each other's memory? I can't think of any other explanation for the two streams working fine individually, but when both are enabled at the same time the output is garbled. I've tried all sorts of things like tying them to the same source block, removing the upsampling/downsampling, adding a delay to one, etc. with no luck.

[1] "Flowgraph with two parallel streams both using the custom block pq_rails": https://github.com/regulatre/gr-powerquality/blob/master/examples/streamer.grc

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