diff options
author | Takashi Iwai <tiwai@suse.de> | 2016-09-01 14:05:00 +0200 |
---|---|---|
committer | Takashi Iwai <tiwai@suse.de> | 2016-09-02 10:13:48 +0200 |
commit | 0fc4b4d17bfd0ce44394f6040e1d5f9dfa97a5ad (patch) | |
tree | 6aaa0ce1209f0e62dfb812c250d19843bb839744 | |
parent | 3b08152f68b0215474f5fc2d18681d6597a77a3c (diff) | |
download | alsa-lib-0fc4b4d17bfd0ce44394f6040e1d5f9dfa97a5ad.tar.gz |
pcm: Better understandable locking code
The newly added locking code seems to have confused quite a few
people, as "thread_safe=1" may be considered as if the thread-safety
lock has to be turned on. (It meant that the plugin _is_ thread-safe,
i.e. it needs no extra locking.)
For avoiding such a misunderstanding, this commit renames the relevant
pcm fields and give more comments to explain what is for what.
The former single pcm->thread_safe flag is now split to two boolean
flags, pcm->need_lock and pcm->lock_enabled. It consumes a few more
bytes, but this would be (hopefully) better understandable.
No functional change by this commit.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
-rw-r--r-- | src/pcm/pcm.c | 16 | ||||
-rw-r--r-- | src/pcm/pcm_hw.c | 2 | ||||
-rw-r--r-- | src/pcm/pcm_local.h | 27 |
3 files changed, 34 insertions, 11 deletions
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index f8323999..cd87bc75 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -2545,14 +2545,20 @@ int snd_pcm_new(snd_pcm_t **pcmp, snd_pcm_type_t type, const char *name, INIT_LIST_HEAD(&pcm->async_handlers); #ifdef THREAD_SAFE_API pthread_mutex_init(&pcm->lock, NULL); + /* use locking as default; + * each plugin may suppress this in its open call + */ + pcm->need_lock = 1; { - static int default_thread_safe = -1; - if (default_thread_safe < 0) { + /* set lock_enabled field depending on $LIBASOUND_THREAD_SAFE */ + static int do_lock_enable = -1; /* uninitialized */ + + /* evaluate env var only once at the first open for consistency */ + if (do_lock_enable == -1) { char *p = getenv("LIBASOUND_THREAD_SAFE"); - default_thread_safe = !p || *p != '0'; + do_lock_enable = !p || *p != '0'; } - if (!default_thread_safe) - pcm->thread_safe = -1; /* force to disable */ + pcm->lock_enabled = do_lock_enable; } #endif *pcmp = pcm; diff --git a/src/pcm/pcm_hw.c b/src/pcm/pcm_hw.c index 3a5634c1..56e88b6b 100644 --- a/src/pcm/pcm_hw.c +++ b/src/pcm/pcm_hw.c @@ -1514,7 +1514,7 @@ int snd_pcm_hw_open_fd(snd_pcm_t **pcmp, const char *name, pcm->poll_events = info.stream == SND_PCM_STREAM_PLAYBACK ? POLLOUT : POLLIN; pcm->tstamp_type = tstamp_type; #ifdef THREAD_SAFE_API - pcm->thread_safe = 1; + pcm->need_lock = 0; /* hw plugin is thread-safe */ #endif ret = snd_pcm_hw_mmap_status(pcm); diff --git a/src/pcm/pcm_local.h b/src/pcm/pcm_local.h index bb7964d7..bba2f15a 100644 --- a/src/pcm/pcm_local.h +++ b/src/pcm/pcm_local.h @@ -244,7 +244,12 @@ struct _snd_pcm { void *private_data; struct list_head async_handlers; #ifdef THREAD_SAFE_API - int thread_safe; + int need_lock; /* true = this PCM (plugin) is thread-unsafe, + * thus it needs a lock. + */ + int lock_enabled; /* thread-safety lock is enabled on the system; + * it's set depending on $LIBASOUND_THREAD_SAFE. + */ pthread_mutex_t lock; #endif }; @@ -1085,24 +1090,36 @@ static inline void sw_set_period_event(snd_pcm_sw_params_t *params, int val) #define PCMINABORT(pcm) (((pcm)->mode & SND_PCM_ABORT) != 0) #ifdef THREAD_SAFE_API +/* + * __snd_pcm_lock() and __snd_pcm_unlock() are used to lock/unlock the plugin + * forcibly even if it's declared as thread-safe. It's needed only for some + * codes that are thread-unsafe per design (e.g. snd_pcm_nonblock()). + * + * OTOH, snd_pcm_lock() and snd_pcm_unlock() are used to lock/unlock the plugin + * in normal situations. They do lock/unlock only when the plugin is + * thread-unsafe. + * + * Both __snd_pcm_lock() and snd_pcm_lock() (and their unlocks) wouldn't do + * any action when the whole locking is disabled via $LIBASOUND_THREAD_SAFE=0. + */ static inline void __snd_pcm_lock(snd_pcm_t *pcm) { - if (pcm->thread_safe >= 0) + if (pcm->lock_enabled) pthread_mutex_lock(&pcm->lock); } static inline void __snd_pcm_unlock(snd_pcm_t *pcm) { - if (pcm->thread_safe >= 0) + if (pcm->lock_enabled) pthread_mutex_unlock(&pcm->lock); } static inline void snd_pcm_lock(snd_pcm_t *pcm) { - if (!pcm->thread_safe) + if (pcm->lock_enabled && pcm->need_lock) pthread_mutex_lock(&pcm->lock); } static inline void snd_pcm_unlock(snd_pcm_t *pcm) { - if (!pcm->thread_safe) + if (pcm->lock_enabled && pcm->need_lock) pthread_mutex_unlock(&pcm->lock); } #else /* THREAD_SAFE_API */ |