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pcm: Better understandable locking code

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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>
This commit is contained in:
Takashi Iwai 2016-09-01 14:05:00 +02:00
parent 3b08152f68
commit 0fc4b4d17b
3 changed files with 34 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

16
src/pcm/pcm.c
View file

@ -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;

2
src/pcm/pcm_hw.c
View file

@ -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);

27
src/pcm/pcm_local.h
View file

@ -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 */