From 67a7b5a99317ca1f92fb6a88542647aa3ad92c4b Mon Sep 17 00:00:00 2001 From: yanghuolin Date: Thu, 15 Nov 2012 03:31:47 -0500 Subject: [PATCH] alsasink: don't use 100% CPU The root cause is that alsa-lib is not thread safe for the same handle. There are two threads in the gstreamer accessing alsa-lib not serilized. The race condition happens when one thread holds the old framebuffer app_ptr position in the kernel, another thread advances the framebuffer app_ptr. when the former thread is scheduled to run again, it overwrites the app_ptr to old value by copying from kernel.Thus,the app_ptr in the upper alsa-lib(pcm_rate) become one period size more advanced than the lower alsa-lib(pcm_hw & kernel). gstreamer uses noblock and poll method to communicate with the alsa-lib. The app_ptr unsync situation as described above makes the poll return immediately because it concludes there is enough space for the ring-buffer via the low-level alsa-lib. The write function returns immediately because it concludes there is not enough space for the ring-buffer from the upper-level alsa-lib. Then the loop of poll and write runs again and again until another period size is available for ring-buffer.This leads to the cpu 100 problem. delay_lock is used to avoid the race condition. Fixes: https://bugzilla.gnome.org/show_bug.cgi?id=690937 --- ext/alsa/gstalsasink.c | 6 ++++++ ext/alsa/gstalsasink.h | 5 +++++ 2 files changed, 11 insertions(+) diff --git a/ext/alsa/gstalsasink.c b/ext/alsa/gstalsasink.c index 1ef6b91..81731b6 100644 --- a/ext/alsa/gstalsasink.c +++ b/ext/alsa/gstalsasink.c @@ -118,6 +118,7 @@ gst_alsasink_finalise (GObject * object) g_free (sink->device); g_mutex_clear (&sink->alsa_lock); + g_mutex_clear (&sink->delay_lock); g_mutex_lock (&output_mutex); --output_ref; @@ -255,6 +256,7 @@ gst_alsasink_init (GstAlsaSink * alsasink) alsasink->handle = NULL; alsasink->cached_caps = NULL; g_mutex_init (&alsasink->alsa_lock); + g_mutex_init (&alsasink->delay_lock); g_mutex_lock (&output_mutex); if (output_ref == 0) { @@ -1011,7 +1013,9 @@ gst_alsasink_write (GstAudioSink * asink, gpointer data, guint length) if (err < 0) { GST_DEBUG_OBJECT (asink, "wait error, %d", err); } else { + GST_DELAY_SINK_LOCK (asink); err = snd_pcm_writei (alsa->handle, ptr, cptr); + GST_DELAY_SINK_UNLOCK (asink); } GST_DEBUG_OBJECT (asink, "written %d frames out of %d", err, cptr); @@ -1057,7 +1061,9 @@ gst_alsasink_delay (GstAudioSink * asink) alsa = GST_ALSA_SINK (asink); + GST_DELAY_SINK_LOCK (asink); res = snd_pcm_delay (alsa->handle, &delay); + GST_DELAY_SINK_UNLOCK (asink); if (G_UNLIKELY (res < 0)) { /* on errors, report 0 delay */ GST_DEBUG_OBJECT (alsa, "snd_pcm_delay returned %d", res); diff --git a/ext/alsa/gstalsasink.h b/ext/alsa/gstalsasink.h index 3a64a92..8c4c1b0 100644 --- a/ext/alsa/gstalsasink.h +++ b/ext/alsa/gstalsasink.h @@ -43,6 +43,10 @@ typedef struct _GstAlsaSinkClass GstAlsaSinkClass; #define GST_ALSA_SINK_LOCK(obj) (g_mutex_lock (GST_ALSA_SINK_GET_LOCK (obj))) #define GST_ALSA_SINK_UNLOCK(obj) (g_mutex_unlock (GST_ALSA_SINK_GET_LOCK (obj))) +#define GST_DELAY_SINK_GET_LOCK(obj) (&GST_ALSA_SINK_CAST (obj)->delay_lock) +#define GST_DELAY_SINK_LOCK(obj) (g_mutex_lock (GST_DELAY_SINK_GET_LOCK (obj))) +#define GST_DELAY_SINK_UNLOCK(obj) (g_mutex_unlock (GST_DELAY_SINK_GET_LOCK (obj))) + /** * GstAlsaSink: * @@ -73,6 +77,7 @@ struct _GstAlsaSink { GstCaps *cached_caps; GMutex alsa_lock; + GMutex delay_lock; }; struct _GstAlsaSinkClass { -- 2.7.4