gstreamer/gst/gstsystemclock.c
Wim Taymans 20b951efc1 gst/gstsystemclock.c: Add some more docs to explain why a FIXME was wrongly added.
Original commit message from CVS:
* gst/gstsystemclock.c: (gst_system_clock_id_wait_jitter_unlocked):
Add some more docs to explain why a FIXME was wrongly added.
2007-12-24 14:35:24 +00:00

555 lines
18 KiB
C

/* GStreamer
* Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
* 2004 Wim Taymans <wim@fluendo.com>
*
* gstsystemclock.c: Default clock, uses the system clock
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/**
* SECTION:gstsystemclock
* @short_description: Default clock that uses the current system time
* @see_also: #GstClock
*
* The GStreamer core provides a GstSystemClock based on the system time.
* Asynchronous callbacks are scheduled from an internal thread.
*
* Clock implementors are encouraged to subclass this systemclock as it
* implements the async notification.
*
* Subclasses can however override all of the important methods for sync and
* async notifications to implement their own callback methods or blocking
* wait operations.
*
* Last reviewed on 2006-03-08 (0.10.4)
*/
#include "gst_private.h"
#include "gstinfo.h"
#include "gstsystemclock.h"
/* Define this to get some extra debug about jitter from each clock_wait */
#undef WAIT_DEBUGGING
/* the one instance of the systemclock */
static GstClock *_the_system_clock = NULL;
static void gst_system_clock_class_init (GstSystemClockClass * klass);
static void gst_system_clock_init (GstSystemClock * clock);
static void gst_system_clock_dispose (GObject * object);
static GstClockTime gst_system_clock_get_internal_time (GstClock * clock);
static guint64 gst_system_clock_get_resolution (GstClock * clock);
static GstClockReturn gst_system_clock_id_wait_jitter (GstClock * clock,
GstClockEntry * entry, GstClockTimeDiff * jitter);
static GstClockReturn gst_system_clock_id_wait_jitter_unlocked
(GstClock * clock, GstClockEntry * entry, GstClockTimeDiff * jitter,
gboolean restart);
static GstClockReturn gst_system_clock_id_wait_async (GstClock * clock,
GstClockEntry * entry);
static void gst_system_clock_id_unschedule (GstClock * clock,
GstClockEntry * entry);
static void gst_system_clock_async_thread (GstClock * clock);
static gboolean gst_system_clock_start_async (GstSystemClock * clock);
static GStaticMutex _gst_sysclock_mutex = G_STATIC_MUTEX_INIT;
static GstClockClass *parent_class = NULL;
/* static guint gst_system_clock_signals[LAST_SIGNAL] = { 0 }; */
GType
gst_system_clock_get_type (void)
{
static GType clock_type = 0;
if (G_UNLIKELY (clock_type == 0)) {
static const GTypeInfo clock_info = {
sizeof (GstSystemClockClass),
NULL,
NULL,
(GClassInitFunc) gst_system_clock_class_init,
NULL,
NULL,
sizeof (GstSystemClock),
0,
(GInstanceInitFunc) gst_system_clock_init,
NULL
};
clock_type = g_type_register_static (GST_TYPE_CLOCK, "GstSystemClock",
&clock_info, 0);
}
return clock_type;
}
static void
gst_system_clock_class_init (GstSystemClockClass * klass)
{
GObjectClass *gobject_class;
GstObjectClass *gstobject_class;
GstClockClass *gstclock_class;
gobject_class = (GObjectClass *) klass;
gstobject_class = (GstObjectClass *) klass;
gstclock_class = (GstClockClass *) klass;
parent_class = g_type_class_peek_parent (klass);
gobject_class->dispose = gst_system_clock_dispose;
gstclock_class->get_internal_time = gst_system_clock_get_internal_time;
gstclock_class->get_resolution = gst_system_clock_get_resolution;
gstclock_class->wait_jitter = gst_system_clock_id_wait_jitter;
gstclock_class->wait_async = gst_system_clock_id_wait_async;
gstclock_class->unschedule = gst_system_clock_id_unschedule;
}
static void
gst_system_clock_init (GstSystemClock * clock)
{
GST_OBJECT_FLAG_SET (clock,
GST_CLOCK_FLAG_CAN_DO_SINGLE_SYNC |
GST_CLOCK_FLAG_CAN_DO_SINGLE_ASYNC |
GST_CLOCK_FLAG_CAN_DO_PERIODIC_SYNC |
GST_CLOCK_FLAG_CAN_DO_PERIODIC_ASYNC);
#if 0
/* Uncomment this to start the async clock thread straight away */
GST_CLOCK_LOCK (clock);
gst_system_clock_start_async (clock);
GST_CLOCK_UNLOCK (clock);
#endif
}
static void
gst_system_clock_dispose (GObject * object)
{
GstClock *clock = (GstClock *) object;
GstSystemClock *sysclock = GST_SYSTEM_CLOCK (clock);
GList *entries;
/* else we have to stop the thread */
GST_OBJECT_LOCK (clock);
sysclock->stopping = TRUE;
/* unschedule all entries */
for (entries = clock->entries; entries; entries = g_list_next (entries)) {
GstClockEntry *entry = (GstClockEntry *) entries->data;
GST_CAT_DEBUG (GST_CAT_CLOCK, "unscheduling entry %p", entry);
entry->status = GST_CLOCK_UNSCHEDULED;
}
g_list_free (clock->entries);
clock->entries = NULL;
GST_CLOCK_BROADCAST (clock);
GST_OBJECT_UNLOCK (clock);
if (sysclock->thread)
g_thread_join (sysclock->thread);
sysclock->thread = NULL;
GST_CAT_DEBUG (GST_CAT_CLOCK, "joined thread");
G_OBJECT_CLASS (parent_class)->dispose (object);
if (_the_system_clock == clock) {
_the_system_clock = NULL;
GST_CAT_DEBUG (GST_CAT_CLOCK, "disposed system clock");
}
}
/**
* gst_system_clock_obtain:
*
* Get a handle to the default system clock. The refcount of the
* clock will be increased so you need to unref the clock after
* usage.
*
* Returns: the default clock.
*
* MT safe.
*/
GstClock *
gst_system_clock_obtain (void)
{
GstClock *clock;
g_static_mutex_lock (&_gst_sysclock_mutex);
clock = _the_system_clock;
if (clock == NULL) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "creating new static system clock");
clock = g_object_new (GST_TYPE_SYSTEM_CLOCK,
"name", "GstSystemClock", NULL);
/* we created the global clock; take ownership so
* we can hand out instances later */
gst_object_ref (clock);
gst_object_sink (GST_OBJECT (clock));
_the_system_clock = clock;
g_static_mutex_unlock (&_gst_sysclock_mutex);
} else {
g_static_mutex_unlock (&_gst_sysclock_mutex);
GST_CAT_DEBUG (GST_CAT_CLOCK, "returning static system clock");
}
/* we ref it since we are a clock factory. */
gst_object_ref (clock);
return clock;
}
/* this thread reads the sorted clock entries from the queue.
*
* It waits on each of them and fires the callback when the timeout occurs.
*
* When an entry in the queue was canceled before we wait for it, it is
* simply skipped.
*
* When waiting for an entry, it can become canceled, in that case we don't
* call the callback but move to the next item in the queue.
*
* MT safe.
*/
static void
gst_system_clock_async_thread (GstClock * clock)
{
GstSystemClock *sysclock = GST_SYSTEM_CLOCK (clock);
GST_CAT_DEBUG (GST_CAT_CLOCK, "enter system clock thread");
GST_OBJECT_LOCK (clock);
/* signal spinup */
GST_CLOCK_BROADCAST (clock);
/* now enter our (almost) infinite loop */
while (!sysclock->stopping) {
GstClockEntry *entry;
GstClockTime requested;
GstClockReturn res;
/* check if something to be done */
while (clock->entries == NULL) {
GST_CAT_DEBUG (GST_CAT_CLOCK, "no clock entries, waiting..");
/* wait for work to do */
GST_CLOCK_WAIT (clock);
GST_CAT_DEBUG (GST_CAT_CLOCK, "got signal");
/* clock was stopping, exit */
if (sysclock->stopping)
goto exit;
}
/* 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;
}
requested = entry->time;
/* now wait for the entry, we already hold the lock */
res =
gst_system_clock_id_wait_jitter_unlocked (clock, (GstClockID) entry,
NULL, FALSE);
switch (res) {
case GST_CLOCK_UNSCHEDULED:
/* entry was unscheduled, move to the next */
GST_CAT_DEBUG (GST_CAT_CLOCK, "async entry %p unscheduled", entry);
goto next_entry;
case GST_CLOCK_OK:
case GST_CLOCK_EARLY:
{
/* entry timed out normally, fire the callback and move to the next
* entry */
GST_CAT_DEBUG (GST_CAT_CLOCK, "async entry %p unlocked", entry);
if (entry->func) {
/* unlock before firing the callback */
GST_OBJECT_UNLOCK (clock);
entry->func (clock, entry->time, (GstClockID) entry,
entry->user_data);
GST_OBJECT_LOCK (clock);
}
if (entry->type == GST_CLOCK_ENTRY_PERIODIC) {
/* adjust time now */
entry->time = requested + entry->interval;
/* and resort the list now */
clock->entries =
g_list_sort (clock->entries, gst_clock_id_compare_func);
/* and restart */
continue;
} else {
goto next_entry;
}
}
case GST_CLOCK_BUSY:
/* somebody unlocked the entry but is was not canceled, This means that
* either a new entry was added in front of the queue or some other entry
* was canceled. Whatever it is, pick the head entry of the list and
* continue waiting. */
GST_CAT_DEBUG (GST_CAT_CLOCK, "async entry %p needs restart", entry);
continue;
default:
GST_CAT_DEBUG (GST_CAT_CLOCK,
"strange result %d waiting for %p, skipping", res, entry);
g_warning ("%s: strange result %d waiting for %p, skipping",
GST_OBJECT_NAME (clock), res, entry);
goto next_entry;
}
next_entry:
/* we remove the current entry and unref it */
clock->entries = g_list_remove (clock->entries, entry);
gst_clock_id_unref ((GstClockID) entry);
}
exit:
/* signal exit */
GST_CLOCK_BROADCAST (clock);
GST_OBJECT_UNLOCK (clock);
GST_CAT_DEBUG (GST_CAT_CLOCK, "exit system clock thread");
}
/* MT safe */
static GstClockTime
gst_system_clock_get_internal_time (GstClock * clock)
{
GTimeVal timeval;
g_get_current_time (&timeval);
return GST_TIMEVAL_TO_TIME (timeval);
}
static guint64
gst_system_clock_get_resolution (GstClock * clock)
{
return 1 * GST_USECOND;
}
/* 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.
*
* Note that signaling the global GCond 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
gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
GstClockEntry * entry, GstClockTimeDiff * jitter, gboolean restart)
{
GstClockTime entryt, real, now, target;
GstClockTimeDiff diff;
/* 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);
entryt = GST_CLOCK_ENTRY_TIME (entry);
now = gst_clock_adjust_unlocked (clock, real);
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;
/* Our GCond implementation expects an absolute time against the system clock
* as a timeout value. We use our internal time to get the system time and add
* the expected timeout to it, this gives us the absolute time of the
* timeout. */
target = gst_system_clock_get_internal_time (clock) + diff;
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p"
" target %" GST_TIME_FORMAT
" entry %" GST_TIME_FORMAT
" now %" GST_TIME_FORMAT
" real %" GST_TIME_FORMAT
" diff (entry-now) %" G_GINT64_FORMAT,
entry,
GST_TIME_ARGS (target),
GST_TIME_ARGS (entryt), GST_TIME_ARGS (now), GST_TIME_ARGS (real), diff);
if (diff > 0) {
GTimeVal tv;
#ifdef WAIT_DEBUGGING
GstClockTime result, final;
#endif
GST_TIME_TO_TIMEVAL (target, tv);
while (TRUE) {
/* now wait on the entry, it either times out or the cond is signaled. */
if (!GST_CLOCK_TIMED_WAIT (clock, &tv)) {
/* timeout, this is fine, we can report success now */
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p unlocked after timeout", entry);
entry->status = GST_CLOCK_OK;
#ifdef WAIT_DEBUGGING
real = GST_CLOCK_GET_CLASS (clock)->get_internal_time (clock);
result = gst_clock_adjust_unlocked (clock, real);
final = gst_system_clock_get_internal_time (clock);
GST_CAT_DEBUG (GST_CAT_CLOCK, "Waited for %" G_GINT64_FORMAT
" got %" G_GINT64_FORMAT " diff %" G_GINT64_FORMAT
" %g target-offset %" G_GINT64_FORMAT " %g", entryt, result,
result - entryt,
(double) (GstClockTimeDiff) (result - entryt) / GST_SECOND,
(final - target),
((double) (GstClockTimeDiff) (final - target)) / GST_SECOND);
#endif
break;
} else {
/* the waiting is interrupted because the GCond was signaled. This can
* be because this or some other entry was unscheduled. */
GST_CAT_DEBUG (GST_CAT_CLOCK, "entry %p unlocked with signal", entry);
/* if the entry is unscheduled, we can stop waiting for it, else we
* continue our while loop. */
if (entry->status == GST_CLOCK_UNSCHEDULED)
break;
/* else restart if we must */
if (!restart)
break;
/* 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, "continue waiting for entry %p", entry);
}
}
} else if (diff == 0) {
entry->status = GST_CLOCK_OK;
} else {
entry->status = GST_CLOCK_EARLY;
}
return entry->status;
}
static GstClockReturn
gst_system_clock_id_wait_jitter (GstClock * clock, GstClockEntry * entry,
GstClockTimeDiff * jitter)
{
GstClockReturn ret;
GST_OBJECT_LOCK (clock);
ret = gst_system_clock_id_wait_jitter_unlocked (clock, entry, jitter, TRUE);
GST_OBJECT_UNLOCK (clock);
return ret;
}
/* Start the async clock thread. Must be called with the object lock
* held */
static gboolean
gst_system_clock_start_async (GstSystemClock * clock)
{
GError *error = NULL;
if (clock->thread != NULL)
return TRUE; /* Thread already running. Nothing to do */
clock->thread = g_thread_create ((GThreadFunc) gst_system_clock_async_thread,
clock, TRUE, &error);
if (error)
goto no_thread;
/* wait for it to spin up */
GST_CLOCK_WAIT (clock);
return TRUE;
/* ERRORS */
no_thread:
{
g_warning ("could not create async clock thread: %s", error->message);
}
return FALSE;
}
/* Add an entry to the list of pending async waits. The entry is inserted
* in sorted order. If we inserted the entry at the head of the list, we
* need to signal the thread as it might either be waiting on it or waiting
* for a new entry.
*
* MT safe.
*/
static GstClockReturn
gst_system_clock_id_wait_async (GstClock * clock, GstClockEntry * entry)
{
GST_CAT_DEBUG (GST_CAT_CLOCK, "adding async entry %p", entry);
GST_OBJECT_LOCK (clock);
/* Start the clock async thread if needed */
if (!gst_system_clock_start_async (GST_SYSTEM_CLOCK (clock)))
goto thread_error;
/* need to take a ref */
gst_clock_id_ref ((GstClockID) entry);
/* insert the entry in sorted order */
clock->entries = g_list_insert_sorted (clock->entries, entry,
gst_clock_id_compare_func);
/* only need to send the signal if the entry was added to the
* 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, sending signal");
/* this will wake up _all_ entries waiting for the clock because we have
* only one cond for all entries (makes allocation faster). Entries that
* have not timed out will have their status set to BUSY and should continue
* to wait. In the case of the async ones, the new head entry should be
* taken and waited for. */
GST_CLOCK_BROADCAST (clock);
}
GST_OBJECT_UNLOCK (clock);
return GST_CLOCK_OK;
thread_error:
/* Could not start the async clock thread */
return GST_CLOCK_ERROR;
}
/* unschedule an entry. This will set the state of the entry to GST_CLOCK_UNSCHEDULED
* and will signal any thread waiting for entries to recheck their entry.
* We cannot really decide if the signal is needed or not because the entry
* could be waited on in async or sync mode.
*
* MT safe.
*/
static void
gst_system_clock_id_unschedule (GstClock * clock, GstClockEntry * entry)
{
GST_CAT_DEBUG (GST_CAT_CLOCK, "unscheduling entry %p", entry);
GST_OBJECT_LOCK (clock);
/* mark entry as unscheduled, then wake up all entries. The entries that did
* not timeout will be woken up but immediatly go to sleep again because their
* status would still be busy. */
entry->status = GST_CLOCK_UNSCHEDULED;
GST_CAT_DEBUG (GST_CAT_CLOCK, "sending signal");
GST_CLOCK_BROADCAST (clock);
GST_OBJECT_UNLOCK (clock);
}