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clock: make sync clock wait lockfree

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Make the common case lockfree.
This commit is contained in:
Wim Taymans 2010-10-21 18:08:51 +02:00
parent f4e57cee5d
commit ba7157dce6
3 changed files with 111 additions and 84 deletions
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2
gst/gstclock.c
View file

@ -203,6 +203,8 @@ gst_clock_entry_new (GstClock * clock, GstClockTime time,
entry->func = NULL;
entry->user_data = NULL;
entry->destroy_data = NULL;
entry->unscheduled = FALSE;
entry->woken_up = FALSE;
return (GstClockID) entry;
}

6
gst/gstclock.h
View file

@ -260,6 +260,7 @@ typedef gboolean (*GstClockCallback) (GstClock *clock, GstClockTime time,
* @GST_CLOCK_BADTIME: A bad time was provided to a function.
* @GST_CLOCK_ERROR: An error occurred
* @GST_CLOCK_UNSUPPORTED: Operation is not supported
* @GST_CLOCK_DONE: The ClockID is done waiting
*
* The return value of a clock operation.
*/
@ -271,7 +272,8 @@ typedef enum
GST_CLOCK_BUSY = 3,
GST_CLOCK_BADTIME = 4,
GST_CLOCK_ERROR = 5,
GST_CLOCK_UNSUPPORTED = 6
GST_CLOCK_UNSUPPORTED = 6,
GST_CLOCK_DONE = 7
} GstClockReturn;
/**
@ -349,6 +351,8 @@ struct _GstClockEntry {
GstClockCallback func;
gpointer user_data;
GDestroyNotify destroy_data;
gboolean unscheduled;
gboolean woken_up;
};
/**

183
gst/gstsystemclock.c
View file

@ -53,6 +53,11 @@
# undef WIN32_LEAN_AND_MEAN
#endif /* G_OS_WIN32 */
#define GET_ENTRY_STATUS(e) (g_atomic_int_get(&GST_CLOCK_ENTRY_STATUS(e)))
#define SET_ENTRY_STATUS(e,val) (g_atomic_int_set(&GST_CLOCK_ENTRY_STATUS(e),(val)))
#define CAS_ENTRY_STATUS(e,old,val) (g_atomic_int_compare_and_exchange(\
((volatile gint *)&GST_CLOCK_ENTRY_STATUS(e)), (old), (val)))
/* Define this to get some extra debug about jitter from each clock_wait */
#undef WAIT_DEBUGGING
@ -197,7 +202,7 @@ gst_system_clock_dispose (GObject * object)
GstClockEntry *entry = (GstClockEntry *) entries->data;
GST_CAT_DEBUG (GST_CAT_CLOCK, "unscheduling entry %p", entry);
entry->status = GST_CLOCK_UNSCHEDULED;
SET_ENTRY_STATUS (entry, GST_CLOCK_UNSCHEDULED);
}
GST_CLOCK_BROADCAST (clock);
gst_system_clock_add_wakeup (sysclock);
@ -387,11 +392,7 @@ gst_system_clock_async_thread (GstClock * clock)
/* pick the next entry */
entry = clock->entries->data;
/* if it was unscheduled, just move on to the next entry */
if (entry->status == GST_CLOCK_UNSCHEDULED) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p was unscheduled", entry);
goto next_entry;
}
GST_OBJECT_UNLOCK (clock);
requested = entry->time;
@ -400,6 +401,8 @@ gst_system_clock_async_thread (GstClock * clock)
gst_system_clock_id_wait_jitter_unlocked (clock, (GstClockID) entry,
NULL, FALSE);
GST_OBJECT_LOCK (clock);
switch (res) {
case GST_CLOCK_UNSCHEDULED:
/* entry was unscheduled, move to the next */
@ -442,7 +445,7 @@ gst_system_clock_async_thread (GstClock * clock)
/* we set the entry back to the OK state. This is needed so that the
* _unschedule() code can see if an entry is currently being waited
* on (when its state is BUSY). */
entry->status = GST_CLOCK_OK;
SET_ENTRY_STATUS (entry, GST_CLOCK_OK);
continue;
default:
GST_CAT_DEBUG (GST_CAT_CLOCK,
@ -549,18 +552,16 @@ gst_system_clock_get_resolution (GstClock * clock)
/* synchronously wait on the given GstClockEntry.
*
* We do this by blocking on the global clock GCond variable with
* the requested time as a timeout. This allows us to unblock the
* entry by signaling the GCond variable.
* We do this by blocking on the global GstPoll timer with
* the requested timeout. This allows us to unblock the
* entry by writing on the control fd.
*
* Note that signaling the global GCond unlocks all waiting entries. So
* Note that writing the global GstPoll unlocks all waiting entries. So
* we need to check if an unlocked entry has changed when it unlocks.
*
* Entries that arrive too late are simply not waited on and a
* GST_CLOCK_EARLY result is returned.
*
* should be called with LOCK held.
*
* MT safe.
*/
static GstClockReturn
@ -568,78 +569,95 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
GstClockEntry * entry, GstClockTimeDiff * jitter, gboolean restart)
{
GstSystemClock *sysclock = GST_SYSTEM_CLOCK_CAST (clock);
GstClockTime entryt, real, now;
GstClockTime entryt, now;
GstClockTimeDiff diff;
GstClockReturn status;
if (G_UNLIKELY (GET_ENTRY_STATUS (entry) == GST_CLOCK_UNSCHEDULED))
return GST_CLOCK_UNSCHEDULED;
/* need to call the overridden method because we want to sync against the time
* of the clock, whatever the subclass uses as a clock. */
real = GST_CLOCK_GET_CLASS (clock)->get_internal_time (clock);
now = gst_clock_adjust_unlocked (clock, real);
now = gst_clock_get_time (clock);
/* get the time of the entry */
entryt = GST_CLOCK_ENTRY_TIME (entry);
if (jitter) {
*jitter = GST_CLOCK_DIFF (entryt, now);
}
/* the diff of the entry with the clock is the amount of time we have to
* wait */
diff = entryt - now;
diff = GST_CLOCK_DIFF (now, entryt);
if (G_LIKELY (jitter))
*jitter = -diff;
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p"
" time %" GST_TIME_FORMAT
" now %" GST_TIME_FORMAT
" real %" GST_TIME_FORMAT
" diff (time-now) %" G_GINT64_FORMAT,
entry,
GST_TIME_ARGS (entryt), GST_TIME_ARGS (now), GST_TIME_ARGS (real), diff);
entry, GST_TIME_ARGS (entryt), GST_TIME_ARGS (now), diff);
if (diff > 0) {
if (G_LIKELY (diff > 0)) {
#ifdef WAIT_DEBUGGING
GstClockTime final;
#endif
while (entry->status != GST_CLOCK_UNSCHEDULED) {
while (TRUE) {
gint pollret;
/* mark the entry as busy */
entry->status = GST_CLOCK_BUSY;
GST_OBJECT_UNLOCK (clock);
do {
status = GET_ENTRY_STATUS (entry);
/* now wait on the entry, it either times out or the fd is written. */
/* stop when we are unscheduled */
if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED))
goto done;
/* mark the entry as busy but watch out for intermediate unscheduled
* statuses */
} while (G_UNLIKELY (!CAS_ENTRY_STATUS (entry, status, GST_CLOCK_BUSY)));
/* now wait on the entry, it either times out or the fd is written. The
* status of the entry is only BUSY around the poll. */
pollret = gst_poll_wait (sysclock->priv->timer, diff);
/* another thread can read the fd before we get the lock */
GST_OBJECT_LOCK (clock);
if (entry->status == GST_CLOCK_UNSCHEDULED) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p unlocked", entry);
/* get the new status, mark as DONE. We do this so that the unschedule
* function knows when we left the poll and doesn't need to wakeup the
* poll anymore. */
do {
status = GET_ENTRY_STATUS (entry);
/* we were unscheduled, exit immediately */
if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED))
break;
} while (G_UNLIKELY (!CAS_ENTRY_STATUS (entry, status, GST_CLOCK_DONE)));
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p unlocked, status %d, ret %d",
entry, status, pollret);
if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED)) {
/* try to clean up The unschedule function managed to set the status to
* unscheduled. We now take the lock and mark the entry as unscheduled.
* This makes sure that the unschedule function doesn't perform a
* wakeup anymore. If the unschedule function has a change to perform
* the wakeup before us, we clean up here */
GST_OBJECT_LOCK (sysclock);
entry->unscheduled = TRUE;
if (entry->woken_up) {
gst_system_clock_remove_wakeup (sysclock);
}
GST_OBJECT_UNLOCK (sysclock);
goto done;
} else {
if (pollret != 0) {
if (G_UNLIKELY (pollret != 0)) {
/* some other id got unlocked */
if (!restart) {
/* this can happen if the entry got unlocked because of an async
* entry was added to the head of the async queue. */
GST_CAT_DEBUG (GST_CAT_CLOCK, "wakeup waiting for entry %p", entry);
break;
goto done;
}
/* mark ourselves as EARLY, we release the lock and we could be
* unscheduled ourselves but we don't want the unscheduling thread
* to write on the control socket (it does that when an entry has a
* BUSY status). */
entry->status = GST_CLOCK_EARLY;
/* wait till all the entries got woken up */
GST_OBJECT_LOCK (sysclock);
gst_system_clock_wait_wakeup (sysclock);
/* we released the lock in the wait, recheck our status, we don't need
* to remove the wakeup count because we marked the entry as EARLY
* before releasing the object lock. */
if (entry->status == GST_CLOCK_UNSCHEDULED) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p got unscheduled", entry);
break;
}
GST_OBJECT_UNLOCK (sysclock);
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p needs to be restarted",
entry);
@ -650,13 +668,13 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
/* reschedule if gst_poll_wait returned early or we have to reschedule after
* an unlock*/
real = GST_CLOCK_GET_CLASS (clock)->get_internal_time (clock);
now = gst_clock_adjust_unlocked (clock, real);
diff = entryt - now;
now = gst_clock_get_time (clock);
diff = GST_CLOCK_DIFF (now, entryt);
if (diff <= 0) {
/* timeout, this is fine, we can report success now */
entry->status = GST_CLOCK_OK;
status = GST_CLOCK_OK;
SET_ENTRY_STATUS (entry, status);
GST_CAT_DEBUG (GST_CAT_CLOCK,
"entry %p finished, diff %" G_GINT64_FORMAT, entry, diff);
@ -671,42 +689,31 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
(final - target),
((double) (GstClockTimeDiff) (final - target)) / GST_SECOND);
#endif
break;
goto done;
} else {
GST_CAT_DEBUG (GST_CAT_CLOCK,
"entry %p restart, diff %" G_GINT64_FORMAT, entry, diff);
}
}
}
} else if (diff == 0) {
entry->status = GST_CLOCK_OK;
} else {
entry->status = GST_CLOCK_EARLY;
/* we are right on time or too late */
if (G_UNLIKELY (diff == 0))
status = GST_CLOCK_OK;
else
status = GST_CLOCK_EARLY;
SET_ENTRY_STATUS (entry, status);
}
return entry->status;
done:
return status;
}
static GstClockReturn
gst_system_clock_id_wait_jitter (GstClock * clock, GstClockEntry * entry,
GstClockTimeDiff * jitter)
{
GstClockReturn ret;
GST_OBJECT_LOCK (clock);
if (G_UNLIKELY (entry->status == GST_CLOCK_UNSCHEDULED))
goto was_unscheduled;
ret = gst_system_clock_id_wait_jitter_unlocked (clock, entry, jitter, TRUE);
GST_OBJECT_UNLOCK (clock);
return ret;
/* ERRORS */
was_unscheduled:
{
GST_OBJECT_UNLOCK (clock);
return GST_CLOCK_UNSCHEDULED;
}
return gst_system_clock_id_wait_jitter_unlocked (clock, entry, jitter, TRUE);
}
/* Start the async clock thread. Must be called with the object lock
@ -760,7 +767,7 @@ gst_system_clock_id_wait_async (GstClock * clock, GstClockEntry * entry)
if (G_UNLIKELY (!gst_system_clock_start_async (sysclock)))
goto thread_error;
if (G_UNLIKELY (entry->status == GST_CLOCK_UNSCHEDULED))
if (G_UNLIKELY (GET_ENTRY_STATUS (entry) == GST_CLOCK_UNSCHEDULED))
goto was_unscheduled;
if (clock->entries)
@ -778,14 +785,20 @@ gst_system_clock_id_wait_async (GstClock * clock, GstClockEntry * entry)
* front, else the thread is just waiting for another entry and
* will get to this entry automatically. */
if (clock->entries->data == entry) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "async entry added to head");
GST_CAT_DEBUG (GST_CAT_CLOCK, "async entry added to head %p", head);
if (head == NULL) {
/* the list was empty before, signal the cond so that the async thread can
* start taking a look at the queue */
GST_CAT_DEBUG (GST_CAT_CLOCK, "first entry, sending signal");
GST_CLOCK_BROADCAST (clock);
} else {
if (head->status == GST_CLOCK_BUSY) {
GstClockReturn status;
status = GET_ENTRY_STATUS (head);
GST_CAT_DEBUG (GST_CAT_CLOCK, "head entry %p status %d", head, status);
if (status == GST_CLOCK_BUSY) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "head entry is busy");
/* the async thread was waiting for an entry, unlock the wait so that it
* looks at the new head entry instead, we only need to do this once */
if (!sysclock->priv->async_wakeup) {
@ -825,21 +838,29 @@ static void
gst_system_clock_id_unschedule (GstClock * clock, GstClockEntry * entry)
{
GstSystemClock *sysclock;
GstClockReturn status;
sysclock = GST_SYSTEM_CLOCK_CAST (clock);
GST_CAT_DEBUG (GST_CAT_CLOCK, "unscheduling entry %p", entry);
GST_OBJECT_LOCK (clock);
if (entry->status == GST_CLOCK_BUSY) {
/* change the entry status to unscheduled */
do {
status = GET_ENTRY_STATUS (entry);
} while (G_UNLIKELY (!CAS_ENTRY_STATUS (entry, status,
GST_CLOCK_UNSCHEDULED)));
if (G_LIKELY (status == GST_CLOCK_BUSY)) {
/* the entry was being busy, wake up all entries so that they recheck their
* status. We cannot wake up just one entry because allocating such a
* datastructure for each entry would be too heavy and unlocking an entry
* is usually done when shutting down or some other exceptional case. */
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry was BUSY, doing wakeup");
if (!entry->unscheduled && !entry->woken_up) {
gst_system_clock_add_wakeup (sysclock);
entry->woken_up = TRUE;
}
}
/* when it leaves the poll, it'll detect the unscheduled */
entry->status = GST_CLOCK_UNSCHEDULED;
GST_OBJECT_UNLOCK (clock);
}