From: Takashi Sakamoto <o-takashi@sakamocchi.jp>
To: perex@perex.cz
Cc: alsa-devel@alsa-project.org
Subject: attach/detach by mixer class implementation of alsa-lib mixer API
Date: Sat, 25 Jun 2022 20:28:39 +0900 [thread overview]
Message-ID: <YrbxZ2b+3rIdi7Ut@workstation> (raw)
Hi Jaroslav,
Recent years I'm bothered about unexpected abort of pulseaudio and
pipewire processes when testing user-defined control element set.
They aborts at element removal event.
```
pulseaudio: mixer.c:149: hctl_elem_event_handler: Assertion `bag_empty(bag)' failed.
wireplumber: mixer.c:149: hctl_elem_event_handler: Assertion `bag_empty(bag)' failed.
```
Would I ask your opinion about the design of alsa-lib mixer API?
As long as I investigate, these programs seem to have careless coding as
alsa-lib mixer API application. Both of them attaches an instance of
snd_mixer_elem_t to an instance of snd_hctl_elem_t by calling
snd_mixer_elem_attach() when detecting element addition, but never detach
it even if detecting element removal.
In the case, the link list (=bag) of mixer API internal never becomes empty.
It has link entries as much as the number of registered mixer classes which
attaches snd_mixer_elem_t. Then it hits the assertion.
I think the design of alsa-lib mixer API demands mixer class implementation
to detach at element removal which attached at element addition. But I have
less conviction about it since enough unfamiliar.
I'm glad if receiving your opinion about it.
I wrote test program for the issued behaviour:
- https://gist.github.com/takaswie/8378fe3bc04652d83428694cd7573bc0
For test, please use sample script in alsa-gobject project:
- https://github.com/alsa-project/alsa-gobject/blob/master/samples/ctl
The patches for pulseaudio/pipewire are prepared:
- https://gitlab.freedesktop.org/takaswie/pulseaudio/-/commit/topic/fix-wrong-handling-alsa-ctl-event
- https://gitlab.freedesktop.org/takaswie/pipewire/-/commits/topic/fix-wrong-handling-alsa-ctl-event
Regards
Takashi Sakamoto
next reply other threads:[~2022-06-25 11:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-25 11:28 Takashi Sakamoto [this message]
2022-06-26 17:23 ` attach/detach by mixer class implementation of alsa-lib mixer API Jaroslav Kysela
2022-06-27 1:28 ` Takashi Sakamoto
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