audio HAL: fix thread starvation

Fix thread starvation issue where the capture or playback threads
running in FIFO priority would constantly acquire the stream mutex preventing
other threads to complete routing commands.

Bug: 21880828.
Change-Id: I36e9c609857dd1bc959809326350a04c3af92228

1 files changed, 3 insertions, 0 deletions

diff --git a/audio/hal/audio_hw.h b/audio/hal/audio_hw.h
index 8563d84..68040ec 100644
--- a/audio/hal/audio_hw.h
+++ b/audio/hal/audio_hw.h
@@ -264,6 +264,7 @@ struct pcm_device {
 struct stream_out {
     struct audio_stream_out     stream;
     pthread_mutex_t             lock; /* see note below on mutex acquisition order */
+    pthread_mutex_t             pre_lock; /* acquire before lock to avoid DOS by playback thread */
     pthread_cond_t              cond;
     struct pcm_config           config;
     struct listnode             pcm_dev_list;
@@ -310,6 +311,8 @@ struct stream_out {
 struct stream_in {
     struct audio_stream_in              stream;
     pthread_mutex_t                     lock; /* see note below on mutex acquisition order */
+    pthread_mutex_t                     pre_lock; /* acquire before lock to avoid DOS by
+                                                     capture thread */
     struct pcm_config                   config;
     struct listnode                     pcm_dev_list;
     int                                 standby;