Re: [Discuss-gnuradio] gri_ringbuffer.{h,cc}

[Robert McGwier]

No.  The problem was caused by our own error.  Under some pathological 
conditions you want to reset the ring buffers and start over.  We talked 
ourselves into believing all off this was protected and we were just 
plain wrong.  I made the initial error and Frank recaptured the error in 
beautiful code.

The final resolution:  if you find pathologies in the ring buffers,  the 
ONLY safe place to reset them is in the callback itself, otherwise the 
callback can /**AND WILL**/ step on the rb reset.  You cannot afford to 
semaphore, etc. in the callback of course, so a safe way is to use flags 
that are only read and reset in the callback when the rb resets occur.  
There are subtle race conditions that might occur but they are minor 
irritants compared to the stupidity of what we were doing.

All of the strange conditions we had in DttSP were caused by this 
programming bug.   They no longer exist in DttSP v.2 which will be out 
next week and they don't exist in PowerSDR now.  We only looked for this 
subtlety for months.  A few well constructed tests finally resolved the 
problem.

Bob



Eric Blossom wrote:
> On Sun, Mar 12, 2006 at 10:20:16PM +0100, Stephane Fillod wrote:
>   
> > - against gnuradio-core: ot_gri_ringbuffer.patch
> >         * src/lib/general/gri_ringbuffer.{cc,h},
> >           src/lib/general/Makefile.am: new lockless ringbuffer (single
> >           reader/single writer) taken from JACK software (GPL).
> >     
>
> Bob and Frank,
>
> Didn't the JACK ringbuffer code cause you problems when pushing "part
> of a float" into it.  I.e., there was room for 3 bytes, but not all
> four.  If this is true, how did you fix it?  Specialize for only
> floats?  "Yet another ringbuffer implementation" that doesn't have
> the problem?  I can't see an occasion when we'd need anything other
> than floats.
>
> Eric
>
>   


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