Re: [Discuss-gnuradio] QT Throw Bad Alloc on flowgraph startup

[(GNU Radio maintainer)]

Hi Tom,

shoot, that sounds like we half-fixed a bug :(
How proficient are you with GDB? Could you get a backtrace? (maybe
based on [1]?)
Thank you!
Marcus

[1] https://wiki.gnuradio.org/index.php/TutorialsGDB

On Fri, 2019-04-26 at 09:25 -0700, Tom McDermott wrote:
> 
> I've had this problem intermittently for about a year.  On starting
> the flowgraph it will terminate
> with QT Throw : Bad Alloc.   Building different versions from about
> 3.7.10 ish to 3.7.latest will change
> whether or not it happens 100% of the time or 30% of the time.
> 
> Today, I noticed that disabling the QT Frequency sink causes it to
> not throw, and the flowgraph runs
> fine.  One input to QT Freq Sink works OK many times, two inputs
> causes it to throw virtually every
> time.
> 
> After some playing around:
> If I change the initial QT Frequency sink to start with a much
> smaller FFT size (256), then it does not
> QT Throw on startup even with two channels.  The original
> configuration was to start at FFT size of 1024
> (causing throw).  Setting the block to start with FFT size of 256
> causes it not to throw.
> 
> When the flowgraph starts, the QT Frequency sink does not display any
> signals.  If, while running
> in GRC, I change the FFT size then suddenly the signal traces start
> displaying.  Also while running
> I can then change the FFT size, and it keeps running, and the display
> shows the effect of changing
> the resolution.
> 
> So I think the QT Throw problem has something to do with the starting
> FFT size, and the non-display
> seems to fix itself after changing the FFT size all related to QT
> Frequency Sink.
> 
> Ubuntu 16.04,  with gnuradio / GRC  3.7.13.5
> 
> -- Tom, N5EG
> 
> 
> 
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