shmsink question

[mattes]

>On Wed, 2011-12-07 at 14:49 -0800, mattes wrote:
>> I feeding gstreamer via the shm interface from my custom app.
>> the file shmpipe.h  outlines shortly how to interact on the server side
>> (acting like a sink/server).
>>
>>  * First, create a writer with sp_writer_create()
>>  * And selectes() on the socket from sp_get_fd()
>>  * If the socket is closed or there are errors from any function, the app
>>  * should call sp_close() and assume the writer is dead
>>  * The server calls sp_writer_accept_client() when there is something to read
>>  * from the server fd
>>  * It then needs to select() on the socket from sp_writer_get_client_fd()
>>  * If it gets an error on that socket, it call sp_writer_close_client().
>>  * If there is something to read, it calls sp_writer_recv().
>>  *
>>  * The writer allocates buffers with sp_writer_alloc_block(),
>>  * writes something in the buffer (retrieved with sp_writer_block_get_buf(),
>>  * then calls  sp_writer_send_buf() to send the buffer or a subsection to
>>  * the other side. When it is done with the block, it calls
>>  * sp_writer_free_block().
>>  * If alloc fails, then the server must wait for events from the clients before
>>  * trying again.
>>
>>
>> One thing that's not clear to me: Do I have to call sp_writer_alloc_block()
>> for every single frame I pass on to sp_writer_send_buf()?
>> Or is sp_writer_alloc_block() simply done once only at startup?
>
>For every frame you want to send, you should allocate a new block. You
>should also know that you can send only a part of a block, you don't
>have to send the whole block. But you should not modify the content of a
>block after doing a send (as it is shared memory). The trivial case is
>alloc_block();get_buf();memcpy();send_buf();free_block();
>
>--
>Olivier Cr?te

thanks for the info, I implemented it as you said.
One first thing I noticed was that alloc_block() returns NULL once in a while.
It seems that a block is not immediately available after free_block().
Does this mean the block is still in use by the consumer(client)?

I then increased the shared memory size for sp_writer_create() to 10* of my frame size and now
I rarely see alloc_block() failing.

Is there magic number for the SHM memory size (set by sp_writer_create()) ?
How many blocks/frames should fit the SHM memory to have a fluent frame flow,
when doing video encoding?

mattes