Hi,
On Oct 02 2018 06:23, Alan Horstmann wrote:
A user of the Portaudio library is reporting that from Alsa version 1.1.4 the function snd_pcm_poll_descriptors() can return -32 (Broken Pipe), and this fails an assert within Portaudio. Earlier 1.1.3 does not seem to show this issue. For more details, see https://app.assembla.com/spaces/portaudio/support/tickets/268.
The Alsa docs don't mention any possible negative error code from this function - has the behaviour changed, or is it likely something else is triggering the difference?
Return values from a call of 'snd_pcm_poll_descriptors()' varies depending on implementation of PCM plugins for used PCM node. Therefore it's impossible to cover all of the values in documentation.
In a design of alsa-lib, 'snd_pcm_poll_descriptors()' is a thin wrapper of '.poll_descriptors' callback of internal/external structure of PCM plugins, therefore its behaviour is dynamically different depending on each implementation.
For example, when using 'hw' PCM node directly, a call of this function can returns '-ENOMEM' or '2': http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm_hw.c;h=59a2...
When using 'dmix' PCM node, '-EIO', '0', '-EPIPE' and '1': http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm_direct.c;h=...
When using PCM node with external PCM plugins such as 'pulse', 'snd_pcm_ioplug_create()' is called to instantiate plugin structure, and a call of 'snd_pcm_poll_descriptors()' can return '-EIO', '0', '1', and value depending on plugin implementation. http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm_ioplug.c;h=...
When having good discussion to investigate cause, discover solution for this kind of issues, you need to identify which PCM node triggers the issue, at least.
Regards
Takashi Sakamoto