gstclock.c 32.8 KB
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/* GStreamer
 * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
 *                    2000 Wim Taymans <wtay@chello.be>
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 *                    2004 Wim Taymans <wim@fluendo.com>
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 *
 * gstclock.c: Clock subsystem for maintaining time sync
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 *
 * 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.
 */
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/**
 * SECTION:gstclock
 * @short_description: Abstract class for global clocks
 * @see_also: #GstSystemClock
 *
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 * GStreamer uses a global clock to synchronize the plugins in a pipeline.
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 * Different clock implementations are possible by implementing this abstract
 * base class.
 *
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 * The #GstClock returns a monotonically increasing time with the method
 * gst_clock_get_time(). Its accuracy and base time depends on the specific clock
 * implementation but time is always expessed in nanoseconds. Since the
 * baseline of the clock is undefined, the clock time returned is not
 * meaningfull in itself, what matters are the deltas between two clock
 * times.
 *
 * The pipeline uses the clock to calculate the stream time.
 * Usually all renderers synchronize to the global clock using the buffer timestamps,
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 * the newsegment events and the element's base time.
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 *
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 * The time of the clock in itself is not very useful for an application.
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 *
 * A clock implementation can support periodic and single shot clock notifications 
 * both synchronous and asynchronous.
 *
 * One first needs to create a #GstClockID for the periodic or single shot
 * notification using gst_clock_new_single_shot_id() or gst_clock_new_periodic_id().
 *
 * To perform a blocking wait for the specific time of the #GstClockID use the
 * gst_clock_id_wait(). To receive a callback when the specific time is reached
 * in the clock use gst_clock_id_wait_async(). Both these calls can be interrupted
 * with the gst_clock_id_unschedule() call. If the blocking wait is unscheduled
 * a return value of GST_CLOCK_UNSCHEDULED is returned.
 *
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 * Periodic callbacks scheduled async will be repeadedly called automatically until
 * it is unscheduled. To schedule an async periodic callback, gst_clock_id_wait() 
 * should be called repeadedly.
 *
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 * The async callbacks can happen from any thread, either provided by the
 * core or from a streaming thread. The application should be prepared for this.
 *
 * A #GstClockID that has been unscheduled cannot be used again for any wait
 * operation.
 *
 * It is possible to perform a blocking wait on the same #GstClockID from multiple
 * threads. However, registering the same #GstClockID for multiple async notifications is
 * not possible, the callback will only be called once.
 *
 * None of the wait operations unref the #GstClockID, the owner is
 * responsible for unreffing the ids itself. This holds for both periodic and
 * single shot notifications. The reason being that the owner of the #GstClockID
 * has to keep a handle to the #GstClockID to unblock the wait on FLUSHING events
 * or state changes and if we unref it automatically, the handle might be
 * invalid.
 *
 * These clock operations do not operate on the stream time, so the callbacks
 * will also occur when not in PLAYING state as if the clock just keeps on
 * running. Some clocks however do not progress when the element that provided
 * the clock is not PLAYING.
 *
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 * When a clock has the GST_CLOCK_FLAG_CAN_SET_MASTER flag set, it can be slaved to
 * another #GstClock with the gst_clock_set_master(). The clock will then 
 * automatically be synchronized to this master clock by repeadedly sampling the
 * master clock and the slave clock and recalibrating the slave clock with
 * gst_clock_set_calibration(). This feature is mostly usefull for plugins that have
 * an internal clock but must operate with another clock selected by the #GstPipeline.
 * They can track the offset and rate difference of their internal clock relative to
 * the master clock by using the gst_clock_get_calibration() function.
 *
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 * Last reviewed on 2005-10-28 (0.9.4)
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 */
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#include <time.h>
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#include "gst_private.h"
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#include "gstclock.h"
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#include "gstinfo.h"
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#include "gstutils.h"
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#ifndef GST_DISABLE_TRACE
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/* #define GST_WITH_ALLOC_TRACE */
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#include "gsttrace.h"
static GstAllocTrace *_gst_clock_entry_trace;
#endif
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/* #define DEBUGGING_ENABLED */

#ifdef DEBUGGING_ENABLED
#define DEBUG(x, args...) g_print (x "\n", ##args)
#else
#define DEBUG(x, args...)       /* nop */
#endif

#define DEFAULT_STATS			FALSE
#define DEFAULT_WINDOW_SIZE		32
#define DEFAULT_WINDOW_THRESHOLD	4
#define DEFAULT_TIMEOUT         	GST_SECOND / 10
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enum
{
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  PROP_0,
  PROP_STATS,
  PROP_WINDOW_SIZE,
  PROP_WINDOW_THRESHOLD,
  PROP_TIMEOUT
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};

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static void gst_clock_class_init (GstClockClass * klass);
static void gst_clock_init (GstClock * clock);
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static void gst_clock_finalize (GObject * object);
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static void gst_clock_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec);
static void gst_clock_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec);
static void gst_clock_update_stats (GstClock * clock);
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static GstObjectClass *parent_class = NULL;
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/* static guint gst_clock_signals[LAST_SIGNAL] = { 0 }; */

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static GstClockID
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gst_clock_entry_new (GstClock * clock, GstClockTime time,
    GstClockTime interval, GstClockEntryType type)
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{
  GstClockEntry *entry;
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  entry = g_malloc0 (sizeof (GstClockEntry));
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#ifndef GST_DISABLE_TRACE
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  gst_alloc_trace_new (_gst_clock_entry_trace, entry);
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#endif
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  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
      "created entry %p, time %" GST_TIME_FORMAT, entry, GST_TIME_ARGS (time));
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  gst_atomic_int_set (&entry->refcount, 1);
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  entry->clock = clock;
  entry->time = time;
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  entry->interval = interval;
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  entry->type = type;
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  entry->status = GST_CLOCK_BUSY;
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  return (GstClockID) entry;
}
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/**
 * gst_clock_id_ref:
 * @id: The clockid to ref
 *
 * Increase the refcount of the given clockid.
 *
 * Returns: The same #GstClockID with increased refcount.
 *
 * MT safe.
 */
GstClockID
gst_clock_id_ref (GstClockID id)
{
  g_return_val_if_fail (id != NULL, NULL);

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  g_atomic_int_inc (&((GstClockEntry *) id)->refcount);
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  return id;
}

static void
_gst_clock_id_free (GstClockID id)
{
  g_return_if_fail (id != NULL);

  GST_CAT_DEBUG (GST_CAT_CLOCK, "freed entry %p", id);

#ifndef GST_DISABLE_TRACE
  gst_alloc_trace_free (_gst_clock_entry_trace, id);
#endif
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  g_free (id);
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}

/**
 * gst_clock_id_unref:
 * @id: The clockid to unref
 *
 * Unref the given clockid. When the refcount reaches 0 the
 * #GstClockID will be freed.
 *
 * MT safe.
 */
void
gst_clock_id_unref (GstClockID id)
{
  gint zero;

  g_return_if_fail (id != NULL);

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  zero = g_atomic_int_dec_and_test (&((GstClockEntry *) id)->refcount);
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  /* if we ended up with the refcount at zero, free the id */
  if (zero) {
    _gst_clock_id_free (id);
  }
}

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/**
 * gst_clock_new_single_shot_id
 * @clock: The clockid to get a single shot notification from
 * @time: the requested time
 *
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 * Get an ID from the given clock to trigger a single shot
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 * notification at the requested time. The single shot id should be
 * unreffed after usage.
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 *
 * Returns: An id that can be used to request the time notification.
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 *
 * MT safe.
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 */
GstClockID
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gst_clock_new_single_shot_id (GstClock * clock, GstClockTime time)
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{
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  g_return_val_if_fail (GST_IS_CLOCK (clock), NULL);

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  return gst_clock_entry_new (clock,
      time, GST_CLOCK_TIME_NONE, GST_CLOCK_ENTRY_SINGLE);
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}

/**
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 * gst_clock_new_periodic_id
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 * @clock: The clockid to get a periodic notification id from
 * @start_time: the requested start time
 * @interval: the requested interval
 *
 * Get an ID from the given clock to trigger a periodic notification.
 * The periodeic notifications will be start at time start_time and
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 * will then be fired with the given interval. The id should be unreffed
 * after usage.
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 *
 * Returns: An id that can be used to request the time notification.
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 *
 * MT safe.
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 */
GstClockID
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gst_clock_new_periodic_id (GstClock * clock, GstClockTime start_time,
    GstClockTime interval)
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{
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  g_return_val_if_fail (GST_IS_CLOCK (clock), NULL);
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  g_return_val_if_fail (GST_CLOCK_TIME_IS_VALID (start_time), NULL);
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  g_return_val_if_fail (interval != 0, NULL);

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  return gst_clock_entry_new (clock,
      start_time, interval, GST_CLOCK_ENTRY_PERIODIC);
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}

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/**
 * gst_clock_id_compare_func
 * @id1: A clockid
 * @id2: A clockid to compare with
 *
 * Compares the two GstClockID instances. This function can be used
 * as a GCompareFunc when sorting ids.
 *
 * Returns: negative value if a < b; zero if a = b; positive value if a > b
 *
 * MT safe.
 */
gint
gst_clock_id_compare_func (gconstpointer id1, gconstpointer id2)
{
  GstClockEntry *entry1, *entry2;

  entry1 = (GstClockEntry *) id1;
  entry2 = (GstClockEntry *) id2;

  if (GST_CLOCK_ENTRY_TIME (entry1) > GST_CLOCK_ENTRY_TIME (entry2)) {
    return 1;
  }
  if (GST_CLOCK_ENTRY_TIME (entry1) < GST_CLOCK_ENTRY_TIME (entry2)) {
    return -1;
  }

  return entry1 - entry2;
}

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/**
 * gst_clock_id_get_time
 * @id: The clockid to query
 *
 * Get the time of the clock ID
 *
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 * Returns: the time of the given clock id.
 *
 * MT safe.
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 */
GstClockTime
gst_clock_id_get_time (GstClockID id)
{
  g_return_val_if_fail (id != NULL, GST_CLOCK_TIME_NONE);

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  return GST_CLOCK_ENTRY_TIME ((GstClockEntry *) id);
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}


/**
 * gst_clock_id_wait
 * @id: The clockid to wait on
 * @jitter: A pointer that will contain the jitter
 *
 * Perform a blocking wait on the given ID. The jitter arg can be
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 * NULL.
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 *
 * Returns: the result of the blocking wait.
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 *
 * MT safe.
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 */
GstClockReturn
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gst_clock_id_wait (GstClockID id, GstClockTimeDiff * jitter)
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{
  GstClockEntry *entry;
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  GstClock *clock;
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  GstClockReturn res;
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  GstClockTime requested;
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  GstClockClass *cclass;
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  g_return_val_if_fail (id != NULL, GST_CLOCK_ERROR);
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  entry = (GstClockEntry *) id;
  requested = GST_CLOCK_ENTRY_TIME (entry);
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  clock = GST_CLOCK_ENTRY_CLOCK (entry);

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  if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (requested)))
    goto invalid_time;

  if (G_UNLIKELY (entry->status == GST_CLOCK_UNSCHEDULED))
    goto unscheduled;
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  cclass = GST_CLOCK_GET_CLASS (clock);
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  if (G_LIKELY (cclass->wait)) {
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    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "waiting on clock entry %p",
        id);
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    res = cclass->wait (clock, entry);
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    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "done waiting entry %p", id);
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    if (jitter) {
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      GstClockTime now = gst_clock_get_time (clock);

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      *jitter = now - requested;
    }
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    if (entry->type == GST_CLOCK_ENTRY_PERIODIC) {
      entry->time += entry->interval;
    }
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    if (clock->stats) {
      gst_clock_update_stats (clock);
    }
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  } else {
    res = GST_CLOCK_UNSUPPORTED;
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  }
  return res;
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  /* ERRORS */
invalid_time:
  {
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    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "invalid time requested, returning _BADTIME");
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    return GST_CLOCK_BADTIME;
  }
unscheduled:
  {
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    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "entry was unscheduled return _UNSCHEDULED");
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    return GST_CLOCK_UNSCHEDULED;
  }
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}

/**
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 * gst_clock_id_wait_async:
 * @id: a #GstClockID to wait on
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 * @func: The callback function
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 * @user_data: User data passed in the calback
 *
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 * Register a callback on the given clockid with the given
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 * function and user_data. When passing an id with an invalid
 * time to this function, the callback will be called immediatly
 * with  a time set to GST_CLOCK_TIME_NONE. The callback will
 * be called when the time of the id has been reached.
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 *
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 * Returns: the result of the non blocking wait.
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 *
 * MT safe.
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 */
GstClockReturn
gst_clock_id_wait_async (GstClockID id,
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    GstClockCallback func, gpointer user_data)
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{
  GstClockEntry *entry;
  GstClock *clock;
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  GstClockReturn res;
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  GstClockClass *cclass;
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  GstClockTime requested;
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  g_return_val_if_fail (id != NULL, GST_CLOCK_ERROR);
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  g_return_val_if_fail (func != NULL, GST_CLOCK_ERROR);
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  entry = (GstClockEntry *) id;
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  requested = GST_CLOCK_ENTRY_TIME (entry);
  clock = GST_CLOCK_ENTRY_CLOCK (entry);
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  if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (requested)))
    goto invalid_time;

  if (G_UNLIKELY (entry->status == GST_CLOCK_UNSCHEDULED))
    goto unscheduled;
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  cclass = GST_CLOCK_GET_CLASS (clock);

  if (cclass->wait_async) {
    entry->func = func;
    entry->user_data = user_data;

    res = cclass->wait_async (clock, entry);
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  } else {
    res = GST_CLOCK_UNSUPPORTED;
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  }
  return res;

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  /* ERRORS */
invalid_time:
  {
    (func) (clock, GST_CLOCK_TIME_NONE, id, user_data);
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    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "invalid time requested, returning _BADTIME");
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    return GST_CLOCK_BADTIME;
  }
unscheduled:
  {
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    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "entry was unscheduled return _UNSCHEDULED");
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    return GST_CLOCK_UNSCHEDULED;
  }
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}

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/**
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 * gst_clock_id_unschedule:
 * @id: The id to unschedule
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 *
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 * Cancel an outstanding request with the given ID. This can either
 * be an outstanding async notification or a pending sync notification.
 * After this call, the @id cannot be used anymore to receive sync or
 * async notifications, you need to create a new GstClockID.
 *
 * MT safe.
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 */
void
gst_clock_id_unschedule (GstClockID id)
{
  GstClockEntry *entry;
  GstClock *clock;
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  GstClockClass *cclass;
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  g_return_if_fail (id != NULL);

  entry = (GstClockEntry *) id;
  clock = entry->clock;
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  cclass = GST_CLOCK_GET_CLASS (clock);

  if (cclass->unschedule)
    cclass->unschedule (clock, entry);
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}

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/**
 * GstClock abstract base class implementation
 */
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GType
gst_clock_get_type (void)
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{
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  static GType clock_type = 0;

  if (!clock_type) {
    static const GTypeInfo clock_info = {
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      sizeof (GstClockClass),
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      NULL,
      NULL,
      (GClassInitFunc) gst_clock_class_init,
      NULL,
      NULL,
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      sizeof (GstClock),
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      0,
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      (GInstanceInitFunc) gst_clock_init,
      NULL
    };
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    clock_type = g_type_register_static (GST_TYPE_OBJECT, "GstClock",
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        &clock_info, G_TYPE_FLAG_ABSTRACT);
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  }
  return clock_type;
}
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static void
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gst_clock_class_init (GstClockClass * klass)
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{
  GObjectClass *gobject_class;
  GstObjectClass *gstobject_class;
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  gobject_class = (GObjectClass *) klass;
  gstobject_class = (GstObjectClass *) klass;
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  parent_class = g_type_class_ref (GST_TYPE_OBJECT);
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  if (!g_thread_supported ())
    g_thread_init (NULL);

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#ifndef GST_DISABLE_TRACE
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  _gst_clock_entry_trace =
      gst_alloc_trace_register (GST_CLOCK_ENTRY_TRACE_NAME);
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#endif
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  gobject_class->finalize = GST_DEBUG_FUNCPTR (gst_clock_finalize);
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  gobject_class->set_property = GST_DEBUG_FUNCPTR (gst_clock_set_property);
  gobject_class->get_property = GST_DEBUG_FUNCPTR (gst_clock_get_property);

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  g_object_class_install_property (G_OBJECT_CLASS (klass), PROP_STATS,
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      g_param_spec_boolean ("stats", "Stats", "Enable clock stats",
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          DEFAULT_STATS, G_PARAM_READWRITE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), PROP_WINDOW_SIZE,
      g_param_spec_int ("window-size", "Window size",
          "The size of the window used to calculate rate and offset", 2, 1024,
          DEFAULT_WINDOW_SIZE, G_PARAM_READWRITE));
  g_object_class_install_property (G_OBJECT_CLASS (klass),
      PROP_WINDOW_THRESHOLD, g_param_spec_int ("window-threshold",
          "Window threshold",
          "The threshold to start calculating rate and offset", 2, 1024,
          DEFAULT_WINDOW_THRESHOLD, G_PARAM_READWRITE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), PROP_TIMEOUT,
      g_param_spec_uint64 ("timeout", "Timeout",
          "The amount of time, in nanoseconds, to sample master and slave clocks",
          0, G_MAXUINT64, DEFAULT_TIMEOUT, G_PARAM_READWRITE));
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}

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static void
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gst_clock_init (GstClock * clock)
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{
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  clock->last_time = 0;
  clock->entries = NULL;
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  clock->entries_changed = g_cond_new ();
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  clock->stats = FALSE;
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  clock->internal_calibration = 0;
  clock->external_calibration = 0;
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  clock->rate_numerator = 1;
  clock->rate_denominator = 1;

  clock->slave_lock = g_mutex_new ();
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  clock->filling = TRUE;
  clock->window_size = DEFAULT_WINDOW_SIZE;
  clock->window_threshold = DEFAULT_WINDOW_THRESHOLD;
  clock->time_index = 0;
  clock->timeout = DEFAULT_TIMEOUT;
  clock->times = g_new0 (GstClockTime, 4 * clock->window_size);
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}

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static void
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gst_clock_finalize (GObject * object)
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{
  GstClock *clock = GST_CLOCK (object);

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  GST_OBJECT_LOCK (clock);
  if (clock->clockid) {
    gst_clock_id_unschedule (clock->clockid);
    gst_clock_id_unref (clock->clockid);
    clock->clockid = NULL;
  }

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  g_cond_free (clock->entries_changed);
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  g_free (clock->times);
  clock->times = NULL;
  GST_OBJECT_UNLOCK (clock);

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  g_mutex_free (clock->slave_lock);

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  G_OBJECT_CLASS (parent_class)->finalize (object);
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}

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/**
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 * gst_clock_set_resolution
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 * @clock: a #GstClock
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 * @resolution: The resolution to set
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 *
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 * Set the accuracy of the clock.
 *
 * Returns: the new resolution of the clock.
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 */
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GstClockTime
gst_clock_set_resolution (GstClock * clock, GstClockTime resolution)
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{
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  GstClockClass *cclass;

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  g_return_val_if_fail (GST_IS_CLOCK (clock), 0);
  g_return_val_if_fail (resolution != 0, 0);
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  cclass = GST_CLOCK_GET_CLASS (clock);

  if (cclass->change_resolution)
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    clock->resolution =
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        cclass->change_resolution (clock, clock->resolution, resolution);
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  return clock->resolution;
}
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/**
 * gst_clock_get_resolution
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 * @clock: a #GstClock
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 *
 * Get the accuracy of the clock.
 *
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 * Returns: the resolution of the clock in units of #GstClockTime.
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 *
 * MT safe.
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 */
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GstClockTime
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gst_clock_get_resolution (GstClock * clock)
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{
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  GstClockClass *cclass;

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  g_return_val_if_fail (GST_IS_CLOCK (clock), 0);
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  cclass = GST_CLOCK_GET_CLASS (clock);

  if (cclass->get_resolution)
    return cclass->get_resolution (clock);
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  return 1;
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}

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/**
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 * gst_clock_adjust_unlocked
 * @clock: a #GstClock to use
 * @internal: a clock time
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 *
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 * Converts the given @internal clock time to the real time, adjusting for the
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 * rate and reference time set with gst_clock_set_calibration() and making sure
 * that the returned time is increasing. This function should be called with the
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 * clock's OBJECT_LOCK held and is mainly used by clock subclasses.
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 *
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 * Returns: the converted time of the clock.
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 *
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 * MT safe.
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 */
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GstClockTime
gst_clock_adjust_unlocked (GstClock * clock, GstClockTime internal)
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{
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  GstClockTime ret;
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  ret = gst_util_uint64_scale (internal - clock->internal_calibration,
      clock->rate_numerator, clock->rate_denominator);
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  ret += clock->external_calibration;
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  /* make sure the time is increasing */
  clock->last_time = MAX (ret, clock->last_time);

  return clock->last_time;
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}

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/**
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 * gst_clock_get_internal_time
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 * @clock: a #GstClock to query
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 *
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 * Gets the current internal time of the given clock. The time is returned
 * unadjusted for the offset and the rate.
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 *
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 * Returns: the internal time of the clock. Or GST_CLOCK_TIME_NONE when
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 * giving wrong input.
 *
 * MT safe.
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 */
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GstClockTime
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gst_clock_get_internal_time (GstClock * clock)
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{
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  GstClockTime ret;
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  GstClockClass *cclass;
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  g_return_val_if_fail (GST_IS_CLOCK (clock), GST_CLOCK_TIME_NONE);
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  cclass = GST_CLOCK_GET_CLASS (clock);
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  if (cclass->get_internal_time) {
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    ret = cclass->get_internal_time (clock);
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  } else {
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    ret = G_GINT64_CONSTANT (0);
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  }
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  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "internal time %" GST_TIME_FORMAT,
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      GST_TIME_ARGS (ret));
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  return ret;
}

/**
 * gst_clock_get_time
 * @clock: a #GstClock to query
 *
 * Gets the current time of the given clock. The time is always
 * monotonically increasing and adjusted according to the current
 * offset and rate.
 *
 * Returns: the time of the clock. Or GST_CLOCK_TIME_NONE when
 * giving wrong input.
 *
 * MT safe.
 */
GstClockTime
gst_clock_get_time (GstClock * clock)
{
  GstClockTime ret;

  g_return_val_if_fail (GST_IS_CLOCK (clock), GST_CLOCK_TIME_NONE);

  ret = gst_clock_get_internal_time (clock);

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  GST_OBJECT_LOCK (clock);
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  /* this will scale for rate and offset */
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  ret = gst_clock_adjust_unlocked (clock, ret);
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  GST_OBJECT_UNLOCK (clock);
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  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "adjusted time %" GST_TIME_FORMAT,
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      GST_TIME_ARGS (ret));
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  return ret;
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}

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/**
 * gst_clock_set_calibration
 * @clock: a #GstClock to calibrate
 * @internal: a reference internal time
 * @external: a reference external time
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 * @rate_num: the numerator of the rate of the clock relative to its
 *            internal time 
 * @rate_denom: the denominator of the rate of the clock
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 *
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 * Adjusts the rate and time of @clock. A rate of 1/1 is the normal speed of
 * the clock. Values bigger than 1/1 make the clock go faster.
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 *
 * @internal and @external are calibration parameters that arrange that
 * gst_clock_get_time() should have been @external at internal time @internal.
 * This internal time should not be in the future; that is, it should be less
 * than the value of gst_clock_get_internal_time() when this function is called.
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 *
 * Subsequent calls to gst_clock_get_time() will return clock times computed as
 * follows:
 *
 * <programlisting>
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 *   time = (internal_time - @internal) * @rate_num / @rate_denom + @external
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 * </programlisting>
 *
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 * This formula is implemented in gst_clock_adjust_unlocked(). Of course, it
 * tries to do the integer arithmetic as precisely as possible.
 *
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 * Note that gst_clock_get_time() always returns increasing values so when you
 * move the clock backwards, gst_clock_get_time() will report the previous value
 * until the clock catches up.
 *
 * MT safe.
 */
void
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gst_clock_set_calibration (GstClock * clock, GstClockTime internal, GstClockTime
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    external, GstClockTime rate_num, GstClockTime rate_denom)
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{
  g_return_if_fail (GST_IS_CLOCK (clock));
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  g_return_if_fail (rate_num > 0);
  g_return_if_fail (rate_denom > 0);
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  g_return_if_fail (internal <= gst_clock_get_internal_time (clock));
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  GST_OBJECT_LOCK (clock);
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  clock->internal_calibration = internal;
  clock->external_calibration = external;
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  clock->rate_numerator = rate_num;
  clock->rate_denominator = rate_denom;
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  GST_OBJECT_UNLOCK (clock);
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}

/**
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 * gst_clock_get_calibration
 * @clock: a #GstClock 
 * @internal: a location to store the internal time
 * @external: a location to store the external time
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 * @rate_num: a location to store the rate numerator
 * @rate_denom: a location to store the rate denominator
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 *
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 * Gets the internal rate and reference time of @clock. See
 * gst_clock_set_calibration() for more information.
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 *
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 * @internal, @external, @rate_num, and @rate_denom can be left NULL if the
 * caller is not interested in the values.
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 *
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 * MT safe.
 */
void
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gst_clock_get_calibration (GstClock * clock, GstClockTime * internal,
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    GstClockTime * external, GstClockTime * rate_num, GstClockTime * rate_denom)
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{
  g_return_if_fail (GST_IS_CLOCK (clock));

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  GST_OBJECT_LOCK (clock);
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  if (rate_num)
    *rate_num = clock->rate_numerator;
  if (rate_denom)
    *rate_denom = clock->rate_denominator;
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  if (external)
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    *external = clock->external_calibration;
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  if (internal)
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    *internal = clock->internal_calibration;
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  GST_OBJECT_UNLOCK (clock);
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}

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/* will be called repeadedly to sample the master and slave clock
 * to recalibrate the clock */
static gboolean
gst_clock_slave_callback (GstClock * master, GstClockTime time,
    GstClockID id, GstClock * clock)
{
  GstClockTime stime, mtime;
  gdouble r_squared;

  stime = gst_clock_get_internal_time (clock);
  mtime = gst_clock_get_time (master);

  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
      "master %" GST_TIME_FORMAT ", slave %" GST_TIME_FORMAT,
      GST_TIME_ARGS (mtime), GST_TIME_ARGS (stime));

  gst_clock_add_observation (clock, stime, mtime, &r_squared);

  /* FIXME, we can use the r_squared value to adjust the timeout
   * value of the clockid */

  return TRUE;
}

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/**
 * gst_clock_set_master
 * @clock: a #GstClock 
 * @master: a master #GstClock 
 *
 * Set @master as the master clock for @clock. @clock will be automatically
 * calibrated so that gst_clock_get_time() reports the same time as the
 * master clock.  
 * 
 * A clock provider that slaves its clock to a master can get the current
 * calibration values with gst_clock_get_calibration().
 *
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 * Returns: TRUE if the clock is capable of being slaved to a master clock.
 *
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 * MT safe.
 */
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gboolean
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gst_clock_set_master (GstClock * clock, GstClock * master)
{
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  g_return_val_if_fail (GST_IS_CLOCK (clock), FALSE);

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  GST_OBJECT_LOCK (clock);
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  /* we always allow setting the master to NULL */
  if (master && !GST_OBJECT_FLAG_IS_SET (clock, GST_CLOCK_FLAG_CAN_SET_MASTER))
    goto not_supported;

  GST_DEBUG_OBJECT (clock, "slaving to master clock %p", master);
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  gst_object_replace ((GstObject **) & clock->master, (GstObject *) master);
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  GST_OBJECT_UNLOCK (clock);

  GST_CLOCK_SLAVE_LOCK (clock);

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  if (clock->clockid) {
    gst_clock_id_unschedule (clock->clockid);
    gst_clock_id_unref (clock->clockid);
    clock->clockid = NULL;
  }
  if (master) {
    clock->filling = TRUE;
    clock->time_index = 0;
    /* use the master periodic id to schedule sampling and
     * clock calibration. */
    clock->clockid = gst_clock_new_periodic_id (master,
        gst_clock_get_time (master), clock->timeout);
    gst_clock_id_wait_async (clock->clockid,
        (GstClockCallback) gst_clock_slave_callback, clock);
  }
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  GST_CLOCK_SLAVE_UNLOCK (clock);
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  return TRUE;

not_supported:
  {
    GST_DEBUG_OBJECT (clock, "cannot be slaved to a master clock");
    return FALSE;
  }
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}

/**
 * gst_clock_get_master
 * @clock: a #GstClock 
 *
 * Get the master clock that @clock is slaved to or NULL when the clock is
 * not slaved to any master clock.
 *
 * Returns: a master #GstClock or NULL when this clock is not slaved to a master
 * clock. Unref after usage.
 *
 * MT safe.
 */
GstClock *
gst_clock_get_master (GstClock * clock)
{
  GstClock *result = NULL;

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  g_return_val_if_fail (GST_IS_CLOCK (clock), NULL);

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  GST_OBJECT_LOCK (clock);
  if (clock->master)
    result = gst_object_ref (clock->master);
  GST_OBJECT_UNLOCK (clock);

  return result;
}

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/* http://mathworld.wolfram.com/LeastSquaresFitting.html
 * with SLAVE_LOCK
 */
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static gboolean
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do_linear_regression (GstClock * clock, GstClockTime * m_num,
    GstClockTime * m_denom, GstClockTime * b, GstClockTime * xbase,
    gdouble * r_squared)
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{
  GstClockTime *newx, *newy;
  GstClockTime xmin, ymin, xbar, ybar, xbar4, ybar4;
  GstClockTimeDiff sxx, sxy, syy;
  GstClockTime *x, *y;
  gint i, j;
  guint n;

  xbar = ybar = sxx = syy = sxy = 0;

  x = clock->times;
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  y = clock->times + 2;
  n = clock->filling ? clock->time_index : clock->window_size;
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#ifdef DEBUGGING_ENABLED
  DEBUG ("doing regression on:");
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  for (i = j = 0; i < n; i++, j += 4)
    DEBUG ("  %" G_GUINT64_FORMAT "  %" G_GUINT64_FORMAT, x[j], y[j]);
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#endif

  xmin = ymin = G_MAXUINT64;
  for (i = j = 0; i < n; i++, j += 4) {
    xmin = MIN (xmin, x[j]);
    ymin = MIN (ymin, y[j]);
  }

  DEBUG ("min x: %" G_GUINT64_FORMAT, xmin);
  DEBUG ("min y: %" G_GUINT64_FORMAT, ymin);

  newx = clock->times + 1;
  newy = clock->times + 3;

  /* strip off unnecessary bits of precision */
  for (i = j = 0; i < n; i++, j += 4) {
    newx[j] = x[j] - xmin;