gstclock.c

/* GStreamer
 * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
 *                    2000 Wim Taymans <wtay@chello.be>
 *                    2004 Wim Taymans <wim@fluendo.com>
 *
 * gstclock.c: Clock subsystem for maintaining time sync
 *
 * 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:gstclock
 * @short_description: Abstract class for global clocks
 * @see_also: #GstSystemClock, #GstPipeline
 *
 * GStreamer uses a global clock to synchronize the plugins in a pipeline.
 * Different clock implementations are possible by implementing this abstract
 * base class or, more conveniently, by subclassing #GstSystemClock.
 *
 * The #GstClock returns a monotonically increasing time with the method
 * gst_clock_get_time(). Its accuracy and base time depend on the specific
 * clock implementation but time is always expressed in nanoseconds. Since the
 * baseline of the clock is undefined, the clock time returned is not
 * meaningful in itself, what matters are the deltas between two clock times.
 * The time returned by a clock is called the absolute time.
 *
 * The pipeline uses the clock to calculate the running time. Usually all
 * renderers synchronize to the global clock using the buffer timestamps, the
 * newsegment events and the element's base time, see #GstPipeline.
 *
 * 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.
 *
 * Periodic callbacks scheduled async will be repeatedly called automatically
 * until it is unscheduled. To schedule a sync periodic callback,
 * gst_clock_id_wait() should be called repeatedly.
 *
 * 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, a new #GstClockID should be created and the old unscheduled one
 * should be destroyed with gst_clock_id_unref().
 *
 * 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 for
 * the thread registering the entry last.
 *
 * 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 the entry would be unreffed automatically, the handle 
 * might become invalid without any notification.
 *
 * These clock operations do not operate on the running 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.
 *
 * 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 repeatedly
 * sampling the master clock and the slave clock and recalibrating the slave
 * clock with gst_clock_set_calibration(). This feature is mostly useful 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. 
 *
 * The master/slave synchronisation can be tuned with the #GstClock:timeout,
 * #GstClock:window-size and #GstClock:window-threshold properties.
 * The #GstClock:timeout property defines the interval to sample the master
 * clock and run the calibration functions. #GstClock:window-size defines the
 * number of samples to use when calibrating and #GstClock:window-threshold
 * defines the minimum number of samples before the calibration is performed.
 *
 * Last reviewed on 2009-05-21 (0.10.24)
 */


#include "gst_private.h"
#include <time.h>

#include "gstclock.h"
#include "gstinfo.h"
#include "gstutils.h"

#ifndef GST_DISABLE_TRACE
/* #define GST_WITH_ALLOC_TRACE */
#include "gsttrace.h"
static GstAllocTrace *_gst_clock_entry_trace;
#endif

/* #define DEBUGGING_ENABLED */

#define DEFAULT_STATS                   FALSE
#define DEFAULT_WINDOW_SIZE             32
#define DEFAULT_WINDOW_THRESHOLD        4
#define DEFAULT_TIMEOUT                 GST_SECOND / 10

enum
{
  PROP_0,
  PROP_STATS,
  PROP_WINDOW_SIZE,
  PROP_WINDOW_THRESHOLD,
  PROP_TIMEOUT
};

struct _GstClockPrivate
{
  gint pre_count;
  gint post_count;
};

/* seqlocks */
#define read_seqbegin(clock)                                   \
  g_atomic_int_get (&clock->ABI.priv->post_count);

static inline gboolean
read_seqretry (GstClock * clock, gint seq)
{
  /* no retry if the seqnum did not change */
  if (G_LIKELY (seq == g_atomic_int_get (&clock->ABI.priv->pre_count)))
    return FALSE;

  /* wait for the writer to finish and retry */
  GST_OBJECT_LOCK (clock);
  GST_OBJECT_UNLOCK (clock);
  return TRUE;
}

#define write_seqlock(clock)                      \
G_STMT_START {                                    \
  GST_OBJECT_LOCK (clock);                        \
  g_atomic_int_inc (&clock->ABI.priv->pre_count);     \
} G_STMT_END;

#define write_sequnlock(clock)                    \
G_STMT_START {                                    \
  g_atomic_int_inc (&clock->ABI.priv->post_count);    \
  GST_OBJECT_UNLOCK (clock);                      \
} G_STMT_END;

static void gst_clock_dispose (GObject * object);
static void gst_clock_finalize (GObject * object);

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);


static GstObjectClass *parent_class = NULL;

/* static guint gst_clock_signals[LAST_SIGNAL] = { 0 }; */

static GstClockID
gst_clock_entry_new (GstClock * clock, GstClockTime time,
    GstClockTime interval, GstClockEntryType type)
{
  GstClockEntry *entry;

  entry = g_slice_new (GstClockEntry);
#ifndef GST_DISABLE_TRACE
  gst_alloc_trace_new (_gst_clock_entry_trace, entry);
#endif
  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
      "created entry %p, time %" GST_TIME_FORMAT, entry, GST_TIME_ARGS (time));

  entry->refcount = 1;
  entry->clock = clock;
  entry->type = type;
  entry->time = time;
  entry->interval = interval;
  entry->status = GST_CLOCK_OK;
  entry->func = NULL;
  entry->user_data = NULL;
  entry->destroy_data = NULL;

  return (GstClockID) entry;
}

/**
 * gst_clock_id_ref:
 * @id: The #GstClockID to ref
 *
 * Increase the refcount of given @id.
 *
 * Returns: The same #GstClockID with increased refcount.
 *
 * MT safe.
 */
GstClockID
gst_clock_id_ref (GstClockID id)
{
  g_return_val_if_fail (id != NULL, NULL);

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

  return id;
}

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

  GST_CAT_DEBUG (GST_CAT_CLOCK, "freed entry %p", id);
  entry = (GstClockEntry *) id;
  if (entry->destroy_data)
    entry->destroy_data (entry->user_data);

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

/**
 * gst_clock_id_unref:
 * @id: The #GstClockID to unref
 *
 * Unref given @id. 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);

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

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

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

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

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

/**
 * gst_clock_id_compare_func
 * @id1: A #GstClockID
 * @id2: A #GstClockID 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 0;
}

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

  return GST_CLOCK_ENTRY_TIME ((GstClockEntry *) id);
}

/**
 * gst_clock_id_wait
 * @id: The #GstClockID to wait on
 * @jitter: A pointer that will contain the jitter, can be %NULL.
 *
 * Perform a blocking wait on @id. 
 * @id should have been created with gst_clock_new_single_shot_id()
 * or gst_clock_new_periodic_id() and should not have been unscheduled
 * with a call to gst_clock_id_unschedule(). 
 *
 * If the @jitter argument is not %NULL and this function returns #GST_CLOCK_OK
 * or #GST_CLOCK_EARLY, it will contain the difference
 * against the clock and the time of @id when this method was
 * called. 
 * Positive values indicate how late @id was relative to the clock
 * (in which case this function will return #GST_CLOCK_EARLY). 
 * Negative values indicate how much time was spent waiting on the clock 
 * before this function returned.
 *
 * Returns: the result of the blocking wait. #GST_CLOCK_EARLY will be returned
 * if the current clock time is past the time of @id, #GST_CLOCK_OK if 
 * @id was scheduled in time. #GST_CLOCK_UNSCHEDULED if @id was 
 * unscheduled with gst_clock_id_unschedule().
 *
 * MT safe.
 */
GstClockReturn
gst_clock_id_wait (GstClockID id, GstClockTimeDiff * jitter)
{
  GstClockEntry *entry;
  GstClock *clock;
  GstClockReturn res;
  GstClockTime requested;
  GstClockClass *cclass;

  g_return_val_if_fail (id != NULL, GST_CLOCK_ERROR);

  entry = (GstClockEntry *) id;
  requested = GST_CLOCK_ENTRY_TIME (entry);

  clock = GST_CLOCK_ENTRY_CLOCK (entry);

  /* can't sync on invalid times */
  if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (requested)))
    goto invalid_time;

  cclass = GST_CLOCK_GET_CLASS (clock);

  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "waiting on clock entry %p", id);

  /* if we have a wait_jitter function, use that */
  if (G_LIKELY (cclass->wait_jitter)) {
    res = cclass->wait_jitter (clock, entry, jitter);
  } else {
    /* check if we have a simple _wait function otherwise. The function without
     * the jitter arg is less optimal as we need to do an additional _get_time()
     * which is not atomic with the _wait() and a typical _wait() function does
     * yet another _get_time() anyway. */
    if (G_UNLIKELY (cclass->wait == NULL))
      goto not_supported;

    if (jitter) {
      GstClockTime now = gst_clock_get_time (clock);

      /* jitter is the diff against the clock when this entry is scheduled. Negative
       * values mean that the entry was in time, a positive value means that the
       * entry was too late. */
      *jitter = GST_CLOCK_DIFF (requested, now);
    }
    res = cclass->wait (clock, entry);
  }

  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
      "done waiting entry %p, res: %d", id, res);

  if (entry->type == GST_CLOCK_ENTRY_PERIODIC)
    entry->time = requested + entry->interval;

  if (G_UNLIKELY (clock->stats))
    gst_clock_update_stats (clock);

  return res;

  /* ERRORS */
invalid_time:
  {
    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "invalid time requested, returning _BADTIME");
    return GST_CLOCK_BADTIME;
  }
not_supported:
  {
    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "clock wait is not supported");
    return GST_CLOCK_UNSUPPORTED;
  }
}

/**
 * gst_clock_id_wait_async_full:
 * @id: a #GstClockID to wait on
 * @func: The callback function
 * @user_data: User data passed in the callback
 * @destroy_data: #GDestroyNotify for user_data
 *
 * Register a callback on the given #GstClockID @id with the given
 * function and user_data. When passing a #GstClockID with an invalid
 * time to this function, the callback will be called immediately
 * with  a time set to GST_CLOCK_TIME_NONE. The callback will
 * be called when the time of @id has been reached.
 *
 * The callback @func can be invoked from any thread, either provided by the
 * core or from a streaming thread. The application should be prepared for this.
 *
 * Returns: the result of the non blocking wait.
 *
 * MT safe.
 *
 * Since: 0.10.30
 */
GstClockReturn
gst_clock_id_wait_async_full (GstClockID id,
    GstClockCallback func, gpointer user_data, GDestroyNotify destroy_data)
{
  GstClockEntry *entry;
  GstClock *clock;
  GstClockReturn res;
  GstClockClass *cclass;
  GstClockTime requested;

  g_return_val_if_fail (id != NULL, GST_CLOCK_ERROR);
  g_return_val_if_fail (func != NULL, GST_CLOCK_ERROR);

  entry = (GstClockEntry *) id;
  requested = GST_CLOCK_ENTRY_TIME (entry);
  clock = GST_CLOCK_ENTRY_CLOCK (entry);

  /* can't sync on invalid times */
  if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (requested)))
    goto invalid_time;

  cclass = GST_CLOCK_GET_CLASS (clock);

  if (G_UNLIKELY (cclass->wait_async == NULL))
    goto not_supported;

  entry->func = func;
  entry->user_data = user_data;
  entry->destroy_data = destroy_data;

  res = cclass->wait_async (clock, entry);

  return res;

  /* ERRORS */
invalid_time:
  {
    (func) (clock, GST_CLOCK_TIME_NONE, id, user_data);
    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "invalid time requested, returning _BADTIME");
    return GST_CLOCK_BADTIME;
  }
not_supported:
  {
    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "clock wait is not supported");
    return GST_CLOCK_UNSUPPORTED;
  }
}

/**
 * gst_clock_id_wait_async:
 * @id: a #GstClockID to wait on
 * @func: The callback function
 * @user_data: User data passed in the callback
 *
 * Register a callback on the given #GstClockID @id with the given
 * function and user_data. When passing a #GstClockID with an invalid
 * time to this function, the callback will be called immediately
 * with  a time set to GST_CLOCK_TIME_NONE. The callback will
 * be called when the time of @id has been reached.
 *
 * The callback @func can be invoked from any thread, either provided by the
 * core or from a streaming thread. The application should be prepared for this.
 *
 * Returns: the result of the non blocking wait.
 *
 * MT safe.
 */
GstClockReturn
gst_clock_id_wait_async (GstClockID id,
    GstClockCallback func, gpointer user_data)
{
  return gst_clock_id_wait_async_full (id, func, user_data, NULL);
}

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

  g_return_if_fail (id != NULL);

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

  cclass = GST_CLOCK_GET_CLASS (clock);

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


/*
 * GstClock abstract base class implementation
 */
G_DEFINE_TYPE (GstClock, gst_clock, GST_TYPE_OBJECT);

static void
gst_clock_class_init (GstClockClass * klass)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

  parent_class = g_type_class_peek_parent (klass);

#ifndef GST_DISABLE_TRACE
  _gst_clock_entry_trace =
      gst_alloc_trace_register (GST_CLOCK_ENTRY_TRACE_NAME);
#endif

  gobject_class->dispose = gst_clock_dispose;
  gobject_class->finalize = gst_clock_finalize;
  gobject_class->set_property = gst_clock_set_property;
  gobject_class->get_property = gst_clock_get_property;

  g_object_class_install_property (gobject_class, PROP_STATS,
      g_param_spec_boolean ("stats", "Stats",
          "Enable clock stats (unimplemented)", DEFAULT_STATS,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, 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_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, 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_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, 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 | G_PARAM_STATIC_STRINGS));

  g_type_class_add_private (klass, sizeof (GstClockPrivate));
}

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

  clock->ABI.priv =
      G_TYPE_INSTANCE_GET_PRIVATE (clock, GST_TYPE_CLOCK, GstClockPrivate);

  clock->internal_calibration = 0;
  clock->external_calibration = 0;
  clock->rate_numerator = 1;
  clock->rate_denominator = 1;

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

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

  GST_OBJECT_LOCK (clock);
  master_p = &clock->master;
  gst_object_replace ((GstObject **) master_p, NULL);
  GST_OBJECT_UNLOCK (clock);

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

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

  GST_CLOCK_SLAVE_LOCK (clock);
  if (clock->clockid) {
    gst_clock_id_unschedule (clock->clockid);
    gst_clock_id_unref (clock->clockid);
    clock->clockid = NULL;
  }
  g_free (clock->times);
  clock->times = NULL;
  GST_CLOCK_SLAVE_UNLOCK (clock);

  g_cond_free (clock->entries_changed);
  g_mutex_free (clock->slave_lock);

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

/**
 * gst_clock_set_resolution
 * @clock: a #GstClock
 * @resolution: The resolution to set
 *
 * Set the accuracy of the clock. Some clocks have the possibility to operate
 * with different accuracy at the expense of more resource usage. There is
 * normally no need to change the default resolution of a clock. The resolution
 * of a clock can only be changed if the clock has the
 * #GST_CLOCK_FLAG_CAN_SET_RESOLUTION flag set.
 *
 * Returns: the new resolution of the clock.
 */
GstClockTime
gst_clock_set_resolution (GstClock * clock, GstClockTime resolution)
{
  GstClockClass *cclass;

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

  cclass = GST_CLOCK_GET_CLASS (clock);

  if (cclass->change_resolution)
    clock->resolution =
        cclass->change_resolution (clock, clock->resolution, resolution);

  return clock->resolution;
}

/**
 * gst_clock_get_resolution
 * @clock: a #GstClock
 *
 * Get the accuracy of the clock. The accuracy of the clock is the granularity
 * of the values returned by gst_clock_get_time().
 *
 * Returns: the resolution of the clock in units of #GstClockTime.
 *
 * MT safe.
 */
GstClockTime
gst_clock_get_resolution (GstClock * clock)
{
  GstClockClass *cclass;

  g_return_val_if_fail (GST_IS_CLOCK (clock), 0);

  cclass = GST_CLOCK_GET_CLASS (clock);

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

  return 1;
}

/**
 * gst_clock_adjust_unlocked
 * @clock: a #GstClock to use
 * @internal: a clock time
 *
 * Converts the given @internal clock time to the external time, adjusting for the
 * 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
 * clock's OBJECT_LOCK held and is mainly used by clock subclasses.
 *
 * This function is the reverse of gst_clock_unadjust_unlocked().
 *
 * Returns: the converted time of the clock.
 */
GstClockTime
gst_clock_adjust_unlocked (GstClock * clock, GstClockTime internal)
{
  GstClockTime ret, cinternal, cexternal, cnum, cdenom;

  /* get calibration values for readability */
  cinternal = clock->internal_calibration;
  cexternal = clock->external_calibration;
  cnum = clock->rate_numerator;
  cdenom = clock->rate_denominator;

  /* avoid divide by 0 */
  if (G_UNLIKELY (cdenom == 0))
    cnum = cdenom = 1;

  /* The formula is (internal - cinternal) * cnum / cdenom + cexternal
   *
   * Since we do math on unsigned 64-bit ints we have to special case for
   * internal < cinternal to get the sign right. this case is not very common,
   * though.
   */
  if (G_LIKELY (internal >= cinternal)) {
    ret = internal - cinternal;
    ret = gst_util_uint64_scale (ret, cnum, cdenom);
    ret += cexternal;
  } else {
    ret = cinternal - internal;
    ret = gst_util_uint64_scale (ret, cnum, cdenom);
    /* clamp to 0 */
    if (G_LIKELY (cexternal > ret))
      ret = cexternal - ret;
    else
      ret = 0;
  }

  /* make sure the time is increasing */
  clock->last_time = MAX (ret, clock->last_time);

  return clock->last_time;
}

/**
 * gst_clock_unadjust_unlocked
 * @clock: a #GstClock to use
 * @external: an external clock time
 *
 * Converts the given @external clock time to the internal time of @clock,
 * using the rate and reference time set with gst_clock_set_calibration().
 * This function should be called with the clock's OBJECT_LOCK held and
 * is mainly used by clock subclasses.
 *
 * This function is the reverse of gst_clock_adjust_unlocked().
 *
 * Returns: the internal time of the clock corresponding to @external.
 *
 * Since: 0.10.13
 */
GstClockTime
gst_clock_unadjust_unlocked (GstClock * clock, GstClockTime external)
{
  GstClockTime ret, cinternal, cexternal, cnum, cdenom;

  /* get calibration values for readability */
  cinternal = clock->internal_calibration;
  cexternal = clock->external_calibration;
  cnum = clock->rate_numerator;
  cdenom = clock->rate_denominator;

  /* avoid divide by 0 */
  if (G_UNLIKELY (cnum == 0))
    cnum = cdenom = 1;

  /* The formula is (external - cexternal) * cdenom / cnum + cinternal */
  if (G_LIKELY (external >= cexternal)) {
    ret = external - cexternal;
    ret = gst_util_uint64_scale (ret, cdenom, cnum);
    ret += cinternal;
  } else {
    ret = cexternal - external;
    ret = gst_util_uint64_scale (ret, cdenom, cnum);
    if (G_LIKELY (cinternal > ret))
      ret = cinternal - ret;
    else
      ret = 0;
  }
  return ret;
}

/**
 * gst_clock_get_internal_time
 * @clock: a #GstClock to query
 *
 * Gets the current internal time of the given clock. The time is returned
 * unadjusted for the offset and the rate.
 *
 * Returns: the internal time of the clock. Or GST_CLOCK_TIME_NONE when
 * given invalid input.
 *
 * MT safe.
 */
GstClockTime
gst_clock_get_internal_time (GstClock * clock)
{
  GstClockTime ret;
  GstClockClass *cclass;

  g_return_val_if_fail (GST_IS_CLOCK (clock), GST_CLOCK_TIME_NONE);

  cclass = GST_CLOCK_GET_CLASS (clock);

  if (G_UNLIKELY (cclass->get_internal_time == NULL))
    goto not_supported;

  ret = cclass->get_internal_time (clock);

  GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock, "internal time %" GST_TIME_FORMAT,
      GST_TIME_ARGS (ret));

  return ret;

  /* ERRORS */
not_supported:
  {
    GST_CAT_DEBUG_OBJECT (GST_CAT_CLOCK, clock,
        "internal time not supported, return 0");
    return G_GINT64_CONSTANT (0);
  }
}

/**
 * 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
 * given invalid input.
 *
 * MT safe.
 */
GstClockTime
gst_clock_get_time (GstClock * clock)
{
  GstClockTime ret;
  gint seq;

  g_return_val_if_fail (GST_IS_CLOCK (clock), GST_CLOCK_TIME_NONE);

  do {
    /* reget the internal time when we retry to get the most current
     * timevalue */
    ret = gst_clock_get_internal_time (clock);