shm interface problems

[Olivier Crête]

Hi,

All calls to shmpipe.c must be protected by a mutex. Also you can NOT
re-use the buffer before it has been freed by the receiving side. The
shmpipe API is a bit deficient as it's missing a reliable way to
indicate that (fixing it is on my to do list). I suggest allocating a
new buffer every time you want to send.. and discard it after having
called sp_writer_send_buf().

So in ThreadB doing:
mutex_lock();
sblock = sp_writer_alloc_block( spipe, shmbufLen );
shmBuf = sp_writer_block_get_buf( sblock );
mutex_unlock(); // optional if you want to do more than just memcpy() here..
memcpy ( shmBuf, frame, shmbufLen );
mutex_lock(); // optional 
int nc = sp_writer_send_buf( spipe, shmBuf, shmbufLen );
shm_alloc_space_block_dec(sblock);
mutex_unlock();

Olivier

On Wed, 2013-01-16 at 08:51 -0800, mattes wrote:
> I am using shmpipe.c with shmalloc.c, pretty much emulating
> what shmsink does.
> 
> I looked at the shmsink source. But i can't identify any kind of lock you
> mentioned. Any pointers are appreciated.
> 
> Here is what I am doing:
> 
> threadA:
> - create the listener interface. 
>   spipe = sp_writer_create( udSocketName, shmbufLen, FILE_MODE  );
> - wait for incoming connections
>   readsocks = select(highsock+1, &socks, (fd_set *) 0, (fd_set *) 0, &timeout);
> - start gstreamer encoding pipeline
> - receive and prep incoming connection
>          sblock = sp_writer_alloc_block( spipe, shmbufLen );
>          shmBuf = sp_writer_block_get_buf( sblock );
>   to assign a single large shared memory buffer 
> - then use 
>         rc = sp_writer_recv( spipe, client );
>   to monitor the connection
> 
> ThreadB:
> - frame gets fed into shmsink via
>    memcpy ( shmBuf, frame, shmbufLen );
>    int nc = sp_writer_send_buf( spipe, shmBuf, shmbufLen );
> 
> As of now the 'sink' code supports only one connection at a time.
> It is using one large shared memory buffer to have a more efficient
> memory copy.
> 
> Mat
> 
> On Wed, 16 Jan 2013 09:23:15 -0500 Olivier Crête <olivier.crete at collabora.com>
> wrote
> 
> > On Wed, 2013-01-16 at 00:34 -0800, mattes wrote:
> > > Just wondering if anybody does run shm sink/src successfully on
> > > Atom based platforms?
> > 
> > We have, are you using shmpipe.c on your sink side? or the entier
> > GStreamer element? If you're just using shmpipe.c, you must make sure
> > your locking is correct. Otherwise, it sounds like an application
> > problem, maybe run it in valgrind ?
> > 
> > -- 
> > Olivier Crête
> > olivier.crete at collabora.com
> > 
> > _______________________________________________
> > gstreamer-devel mailing list
> > gstreamer-devel at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
> 
> 
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-- 
Olivier Crête
olivier.crete at collabora.com