At Wed, 05 Jun 2013 23:25:15 -0700, Patrick Lai wrote:
- << Jaroslav >>
On 6/5/2013 2:17 AM, Clemens Ladisch wrote:
gsantosh@codeaurora.org wrote:
- HAL issues pause in parallel to the write
This is illegal. http://www.alsa-project.org/main/index.php/SMP_Design says: | The use of returned handles [such as snd_pcm_t*] must be serialized
in
| the application using own locking scheme.
If you want to issue a pause while waiting for data to be written, use non-blocking writes.
Based on my understanding of SMP_Design and response above, pause and write to same PCM device are expected to be serialized. However, my interpretation of following patch is that pause and stop are expected to wakes up process waiting in pcm_lib.c wait_for_avail(). It seems to give me the indication that multiple threads acting on same PCM device is expected.
ALSA: pcm_core: Fix wake_up() optimization
This change fixes the "ALSA: pcm_lib - optimize wake_up() calls for PCM I/O" commit. New sleeping queue is introduced to separate user space and kernel space wake_ups. runtime->nowake is renamed to twake (transfer wake).
Jaroslav: Can you share your thought as you are author of this patch?
I don't understand what's the problem in this thread...
The behavior of PAUSED stream in wait_for_avail() is clear. If it's woken up by some events, it simply goes to sleep again without exiting the loop.
We are facing the following issue and want to understand how ALSA is implemented pause, prepare and write if used asynchronously.
for the every seek operation we issue pause and prepare, till now in all the system the issue of (pause + prepare) commands and write are serialized. we are trying to decouple the write and other operation (pause and prepare) to issue in commands asynchronously.
Assume the case below, write is blocked in wait_for_avail as there is no space for the buffer, in between user issued seek on the same session this triggers pause and prepare operations.
pause command will unblock the thread blocked in wait_for_avail, this unblocked thread once again check if buffer avail and if buffer is not avail it goes for wait in loop. after the pause operation is done, HAL issues prepare in prepare we reset the buffer but never unblock the thread waiting in the wait_for_avail. this results in write thread blocked forever and it never gets unblocked as a result the session is blocked.
please help us to know why the implementation of the pause and prepare is this way and are we allowed to do the pause, prepare and write in asynchronously on the same session in copy interface.
Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel