tree c057055f1fc6c34af5ce2ec2e9c7968c2e814b12
parent 375868455a36cbdaf632bc8c5ab937dc0aba0eb8
author Wu-Cheng Li <wuchengli@google.com> 1510151053 +0800
committer chrome-bot <chrome-bot@chromium.org> 1510242393 -0800

CRAS: alsa-plugin - remove snd_pcm_cras_delay

PCM functions became thread-safe in 1.1.2. Some functions like
snd_pcm_delay and snd_pcm_sw_params_current will hold a lock.
snd_pcm_cras_delay is called by snd_pcm_delay, but
snd_pcm_cras_delay calls snd_pcm_sw_params_current. This causes
a deadlock.

There are several options that are not good:
(1) Define --disable-thread-safety in alsa-lib. This will be
    inconsistent with upstream alsa-lib.
(2) Set snd_pcm_t.need_lock=0. need_lock is in pcm_local.h
    and it's not easy to build with it. Also, need_lock means
    the plugin is thread safe and doesn't need locking in
    alsa-lib. Our plugin is not thread safe.
(3) Not to call snd_pcm_sw_params_current in snd_pcm_cras_delay.
    Calling snd_pcm_sw_params_current in .start introduces a
    similar deadlock. Also it's more accurate to get the latest
    boundary in .delay.
I don't see a good solution. Let's remove snd_pcm_cras_delay.

BUG=chromium:779936
TEST=Run loopback_latency -n 4000 and it does not hang.

Change-Id: I69b143aee2e95f8ef8f1a2c0f1604064255d0017
Reviewed-on: https://chromium-review.googlesource.com/758796
Commit-Ready: Wu-Cheng Li <wuchengli@chromium.org>
Tested-by: Wu-Cheng Li <wuchengli@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>