[PATCH] [hackrf] Fix hackrf receive hangs by checking before each lock wait

[Adrian Chadd]

Err, weirdly I thought I had updated this commit to remove the
comment; lemme do that and resend.


-a

On Mon, 9 Nov 2020 at 10:03, Adrian Chadd <adrian at freebsd.org> wrote:
>
> Fix receive path hangs if another thread closes down the hackrf
> receive whilst this buffer receive function is waiting to be
> woken up.
>
> Now:
>
> * Sleep for up to 100ms each time waiting for the cond to be kicked;
> * Check whether streaming is still enabled each time rather than
>   only when the function is entered.
>
> This fixes hangs where consumers like gqrx via gnuradio
> will do a stop_rx/start_rx very quickly to change something, and
> the buffer receive path is waiting for a buffer.
> ---
>  lib/hackrf/hackrf_source_c.cc | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/lib/hackrf/hackrf_source_c.cc b/lib/hackrf/hackrf_source_c.cc
> index 662d04a..21656f9 100644
> --- a/lib/hackrf/hackrf_source_c.cc
> +++ b/lib/hackrf/hackrf_source_c.cc
> @@ -30,6 +30,7 @@
>
>  #include <stdexcept>
>  #include <iostream>
> +#include <chrono>
>
>  #include <gnuradio/io_signature.h>
>
> @@ -203,8 +204,22 @@ int hackrf_source_c::work( int noutput_items,
>    {
>      std::unique_lock<std::mutex> lock(_buf_mutex);
>
> -    while (_buf_used < 3 && running) // collect at least 3 buffers
> -      _buf_cond.wait( lock );
> +    // XXX adrian - tomorrow, turn this loop into a wait_for (1 second)
> +    // and re-check dev.get / running !
> +    // Otherwise this will hang reasonably reliably if we race where
> +    // receive is stopped in one thread, and we've already passed
> +    // the hackrf_is_streaming() check; we'll never finish this loop
> +    // and consumers (eg gqrx) will fail.
> +
> +    while (_buf_used < 3 && running) { // collect at least 3 buffers
> +      _buf_cond.wait_for( lock , std::chrono::milliseconds(100));
> +
> +      // Re-check whether the device has closed or stopped streaming
> +      if ( _dev.get() )
> +        running = (hackrf_is_streaming( _dev.get() ) == HACKRF_TRUE);
> +      else
> +        running = false;
> +    }
>    }
>
>    if ( ! running )
> --
> 2.28.0
>