[PATCH] Loop in soapy_source_c::work() when readStream() returns SOAPY_SDR_OVERFLOW

[Anton Blanchard]

Hi Sylvain,

On Thu, 16 Apr 2020 09:30:31 +1000
Anton Blanchard <anton at ozlabs.org> wrote:

> Hi Sylvain,
> 
> > Looks to me like this has the potential to just hang and prevent the
> > thread from terminating.
> > This needs bounds. One retry is fine, infinite ones not so much.  
> 
> Good idea, how does this look?

Just checking to see if this is OK to be merged?

Thanks,
Anton

> Anton
> --
> 
> I'm using an Airspy HF+ Discovery with the Soapy driver. Whenever I
> turn AGC off it stops receiving samples.
> 
> On closer inspection, switching AGC off results in samples stalling
> for an extended period (hundreds of milliseconds). As such, we hit the
> timeout in SoapyAirspyHF::readStream() and return SOAPY_SDR_TIMEOUT
> (-1).
> 
> Things go wrong at this point. It takes a long time before
> readStream() is called again, presumably because we returned 0 from
> work(). By this time our buffers have overflown, readStream() returns
> SOAPY_SDR_OVERFLOW (-2) and work() returns 0. We loop forever,
> continually overflowing buffers.
> 
> Fix this by looping in soapy_source_c::work() when ->readStream
> returns SOAPY_SDR_OVERFLOW so that we consume the buffers straight
> away.
> 
> Signed-off-by: Anton Blanchard <anton at ozlabs.org>
> ---
>  lib/soapy/soapy_source_c.cc | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/soapy/soapy_source_c.cc b/lib/soapy/soapy_source_c.cc
> index a645361..5c683c9 100644
> --- a/lib/soapy/soapy_source_c.cc
> +++ b/lib/soapy/soapy_source_c.cc
> @@ -96,9 +96,14 @@ int soapy_source_c::work( int noutput_items,
>  {
>      int flags = 0;
>      long long timeNs = 0;
> -    int ret = _device->readStream(
> -        _stream, &output_items[0],
> -        noutput_items, flags, timeNs);
> +    int ret;
> +    int retries = 1;
> +
> +    do {
> +        ret = _device->readStream(
> +            _stream, &output_items[0],
> +            noutput_items, flags, timeNs);
> +    } while (retries-- && (ret == SOAPY_SDR_OVERFLOW));
>  
>      if (ret < 0) return 0; //call again
>      return ret;