glib/gio/gperiodic.c

/*
 * Copyright © 2010 Codethink Limited
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * licence, 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser 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.
 *
 * Author: Ryan Lortie <desrt@desrt.ca>
 */

#include "config.h"

#include "gperiodic.h"

#include "gio-marshal.h"

/**
 * SECTION:gperiodic
 * @title: GPeriodic
 * @short_description: a periodic event clock
 *
 * #GPeriodic is a periodic event clock that fires a configurable number
 * of times per second and is capable of being put into synch with an
 * external time source.
 *
 * A number of #GPeriodicTickFunc<!-- -->s are registered with
 * g_periodic_add() and are called each time the clock "ticks".
 *
 * The tick functions can report "damage" (ie: updates that need to be
 * performed) that are handled in a "repair" phase that follows all the
 * tick functions having been run.  It is also possible to report damage
 * while the clock is not running, in which case the rate of repairs
 * will be rate limited as if the clock were running.
 *
 * #GPeriodic has a configurable priority range consisting of a high and
 * low value.  Other sources with a priority higher than the high value
 * might starve #GPeriodic and sources with the priority lower than the
 * low value may be starved by #GPeriodic.
 *
 * #GPeriodic will engage in dynamic scheduling with respect to sources
 * that have their priorities within the high to low range.  A given
 * #GPeriodic will ensure that the events dispatched from itself are
 * generally using less than 50% of the CPU (on average) if other tasks
 * are pending.  If no other sources within the range are pending then
 * #GPeriodic will use up to all of the available CPU (which can lead to
 * starvation of lower-priority sources, as mentioned above).  The 50%
 * figure is entirely arbitrary and may change or become configurable in
 * the future.
 *
 * For example, if a #GPeriodic has been set to run at 10Hz and a
 * particular iteration uses 140ms of time, then 2 ticks will be
 * "skipped" to give other sources a chance to run (ie: the next tick
 * will occur 300ms later rather than 100ms later, giving 160ms of time
 * for other sources).
 *
 * This means that the high priority value for #GPeriodic should be set
 * quite high (above anything else) and the low priority value for
 * #GPeriodic should be set lower than everything except true "idle"
 * handlers (ie: things that you want to run only when the program is
 * truly idle).
 *
 * #GPeriodic generally assumes that although the things attached to it
 * may be poorly behaved in terms of non-yielding behaviour (either
 * individually or in aggregate), the other sources on the main loop
 * should be "well behaved".  Other sources should try not to block the
 * CPU for a substantial portion of the periodic interval.
 *
 * The sources attached to a #GPeriodic are permitted to be somewhat
 * less well-behaved because they are generally rendering the UI for the
 * user (which should be done smoothly) and also because they will be
 * throttled by #GPeriodic.
 *
 * #GPeriodic is intended to be used as a paint clock for managing
 * geometry updates and painting of windows.
 *
 * Since: 2.28
 **/

/**
 * GPeriodic:
 *
 * #GPeriodic is an opaque structure type.
 *
 * Since: 2.28
 **/

typedef struct
{
  GPeriodicTickFunc callback;
  gpointer          user_data;
  GDestroyNotify    notify;
  guint             id;
} GPeriodicTick;

typedef struct
{
  GSource    source;
  GPeriodic *periodic;
} GPeriodicSource;

struct _GPeriodicPrivate
{
  GSource *source;            /* GPeriodicSource */
  guint64  last_run;
  guint    blocked;
  guint    hz;
  guint    skip_frames;
  guint    stop_skip_id;
  gint     low_priority;

  GSList  *ticks;             /* List<GPeriodicTick> */

  guint    damaged   : 1;

  /* debug */
  guint    in_tick   : 1;
  guint    in_repair : 1;
};

G_DEFINE_TYPE (GPeriodic, g_periodic, G_TYPE_OBJECT)

#define PERIODIC_FROM_SOURCE(src) (((GPeriodicSource *) (src))->periodic)

enum
{
  PROP_NONE,
  PROP_HZ,
  PROP_HIGH_PRIORITY,
  PROP_LOW_PRIORITY
};

static guint g_periodic_tick;
static guint g_periodic_repair;

static guint64
g_periodic_get_microticks (GPeriodic *periodic)
{
  return g_source_get_time (periodic->priv->source) * periodic->priv->hz;
}

static gboolean
g_periodic_stop_skip (gpointer data)
{
  GPeriodic *periodic = data;

  periodic->priv->skip_frames = 0;

  g_message ("Skipping frames ends");

  periodic->priv->stop_skip_id = 0;

  return FALSE;
}

static void
g_periodic_real_tick (GPeriodic *periodic,
                      gint64     timestamp)
{
  GSList *iter;

  for (iter = periodic->priv->ticks; iter; iter = iter->next)
    {
      GPeriodicTick *tick = iter->data;

      tick->callback (periodic, timestamp, tick->user_data);
    }
}

static void
g_periodic_real_repair (GPeriodic *periodic)
{
  periodic->priv->damaged = FALSE;
}

static void
g_periodic_run (GPeriodic *periodic)
{
  gint64 start, usec;

  g_assert (periodic->priv->blocked == 0);

  start = g_get_monotonic_time ();

  if (periodic->priv->ticks)
    {
      guint64 microseconds;

      periodic->priv->in_tick = TRUE;
      microseconds = periodic->priv->last_run / periodic->priv->hz;
      g_signal_emit (periodic, g_periodic_tick, 0, microseconds);
      periodic->priv->in_tick = FALSE;
    }

  g_assert (periodic->priv->blocked == 0);

  if (periodic->priv->damaged)
    {
      periodic->priv->in_repair = TRUE;
      g_signal_emit (periodic, g_periodic_repair, 0);
      periodic->priv->in_repair = FALSE;
    }

  g_assert (!periodic->priv->damaged);

  usec = g_get_monotonic_time () - start;
  g_assert (usec >= 0);

  /* Take the time it took to render, multiply by two and round down to
   * a whole number of frames.  This ensures that we don't take more
   * than 50% of the CPU with rendering.
   *
   * Examples (at 10fps for easy math.  1 frame = 100ms):
   *
   *   0-49ms to render: no frames skipped
   *
   *     We used less than half of the time to render.  OK.  We will run
   *     the next frame 100ms after this one ran (no skips).
   *
   *   50-99ms to render: 1 frame skipped
   *
   *     We used more than half the time.  Skip one frame so that we run
   *     200ms later rather than 100ms later.  We already used up to
   *     99ms worth of that 200ms window, so that gives 101ms for other
   *     things to run (50%).  For figures closer to 50ms the other
   *     stuff will actually get more than 50%.
   *
   *   100-150ms to render: 2 frames skipped, etc.
   */
  periodic->priv->skip_frames = 2 * usec * periodic->priv->hz / 1000000;

  if (periodic->priv->skip_frames)
    {
      g_message ("Slow painting; (possibly) skipping %d frames\n",
                 periodic->priv->skip_frames);

      if (periodic->priv->stop_skip_id == 0)
        periodic->priv->stop_skip_id =
          g_idle_add_full (periodic->priv->low_priority,
                           g_periodic_stop_skip,
                           periodic, NULL);
    }
}

static gboolean
g_periodic_prepare (GSource *source,
                    gint    *timeout)
{
  GPeriodic *periodic = PERIODIC_FROM_SOURCE (source);

  if ((periodic->priv->ticks || periodic->priv->damaged) && !periodic->priv->blocked)
    /* We need to run. */
    {
      gint64 remaining;
     
      remaining = periodic->priv->last_run + 1000000 * (1 + periodic->priv->skip_frames) -
                  g_periodic_get_microticks (periodic);

      if (remaining > 0)
        /* It's too soon.  Wait some more before running. */
        {
          /* Round-up the timeout.
           *
           * If we round down, then we will quite often wake to discover
           * that not enough time has passed and want to sleep again, so
           * save ourselves the future bother.
           */
          *timeout = (remaining + periodic->priv->hz - 1) / periodic->priv->hz / 1000;

          return FALSE;
        }

      else
        /* Enough time has passed.  Run now. */
        {
          *timeout = 0;
          return TRUE;
        }
    }
  else
    /* We shouldn't be running now at all. */
    {
      *timeout = -1;
      return FALSE;
    }
}

static gboolean
g_periodic_check (GSource *source)
{
  GPeriodic *periodic = PERIODIC_FROM_SOURCE (source);

  if ((periodic->priv->ticks || periodic->priv->damaged) && !periodic->priv->blocked)
    /* We need to run. */
    {
      guint64 now = g_periodic_get_microticks (periodic);

      /* Run if it's not too soon. */
      return !(now < periodic->priv->last_run + 1000000 * (periodic->priv->skip_frames + 1));
    }

  else
    /* We shouldn't be running now at all. */
    return FALSE;
}

static gboolean
g_periodic_dispatch (GSource     *source,
                     GSourceFunc  callback,
                     gpointer     user_data)
{
  GPeriodic *periodic = PERIODIC_FROM_SOURCE (source);
  guint64 elapsed_ticks;
  guint64 now;

  g_assert (periodic->priv->blocked == 0);

  /* Update the last_run.
   *
   * In the normal case we want to add exactly 1 tick to it.  This
   * ensures that the clock runs at the proper rate in the normal case
   * (ie: the dispatch overhead time is not lost).
   *
   * If more than one tick has elapsed, we set it equal to the current
   * time.  This has two purposes:
   *
   *   - sets last_run to something reasonable if the clock is running
   *     for the first time or after a long period of inactivity
   *
   *   - resets our stride if we missed a frame
   */
  now = g_periodic_get_microticks (periodic);
  elapsed_ticks = (now - periodic->priv->last_run) / 1000000;
  g_assert (elapsed_ticks > 0);

  if G_LIKELY (elapsed_ticks == 1)
    periodic->priv->last_run += 1000000;
  else
    periodic->priv->last_run = now;

  g_periodic_run (periodic);

  return TRUE;
}

static void
g_periodic_get_property (GObject *object, guint prop_id,
                         GValue *value, GParamSpec *pspec)
{
  GPeriodic *periodic = G_PERIODIC (object);

  switch (prop_id)
    {
    case PROP_HIGH_PRIORITY:
      g_value_set_int (value, g_source_get_priority (periodic->priv->source));
      break;

    case PROP_LOW_PRIORITY:
      g_value_set_int (value, periodic->priv->low_priority);
      break;

    case PROP_HZ:
      g_value_set_uint (value, periodic->priv->hz);
      break;

    default:
      g_assert_not_reached ();
    }
}

static void
g_periodic_set_property (GObject *object, guint prop_id,
                         const GValue *value, GParamSpec *pspec)
{
  GPeriodic *periodic = G_PERIODIC (object);

  switch (prop_id)
    {
    case PROP_HIGH_PRIORITY:
      g_source_set_priority (periodic->priv->source, g_value_get_int (value));
      break;

    case PROP_LOW_PRIORITY:
      periodic->priv->low_priority = g_value_get_int (value);
      break;

    case PROP_HZ:
      periodic->priv->hz = g_value_get_uint (value);
      break;

    default:
      g_assert_not_reached ();
    }
}

static void
g_periodic_finalize (GObject *object)
{
  GPeriodic *periodic = G_PERIODIC (object);

  g_source_destroy (periodic->priv->source);
  g_source_unref (periodic->priv->source);

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

static void
g_periodic_init (GPeriodic *periodic)
{
  static GSourceFuncs source_funcs = {
    g_periodic_prepare, g_periodic_check, g_periodic_dispatch
  };

  periodic->priv = G_TYPE_INSTANCE_GET_PRIVATE (periodic,
                                                G_TYPE_PERIODIC,
                                                GPeriodicPrivate);

  periodic->priv->source = g_source_new (&source_funcs,
                                         sizeof (GPeriodicSource));
  ((GPeriodicSource *) periodic->priv->source)->periodic = periodic;
  g_source_attach (periodic->priv->source,
                   g_main_context_get_thread_default ());
}

static void
g_periodic_class_init (GPeriodicClass *class)
{
  GObjectClass *object_class = G_OBJECT_CLASS (class);

  class->tick = g_periodic_real_tick;
  class->repair = g_periodic_real_repair;

  object_class->get_property = g_periodic_get_property;
  object_class->set_property = g_periodic_set_property;
  object_class->finalize = g_periodic_finalize;

  g_periodic_tick = g_signal_new ("tick", G_TYPE_PERIODIC,
                                  G_SIGNAL_RUN_LAST,
                                  G_STRUCT_OFFSET(GPeriodicClass, tick),
                                  NULL, NULL, _gio_marshal_VOID__INT64,
                                  G_TYPE_NONE, 1, G_TYPE_INT64);
  g_periodic_repair = g_signal_new ("repair", G_TYPE_PERIODIC,
                                    G_SIGNAL_RUN_LAST,
                                    G_STRUCT_OFFSET (GPeriodicClass, repair),
                                    NULL, NULL, g_cclosure_marshal_VOID__VOID,
                                    G_TYPE_NONE, 0);

  g_object_class_install_property (object_class, PROP_HZ,
    g_param_spec_uint ("hz", "ticks per second",
                       "rate (in Hz) at which the 'tick' signal is emitted",
                       1, 120, 1, G_PARAM_READWRITE |
                       G_PARAM_CONSTRUCT_ONLY | G_PARAM_STATIC_STRINGS));

  g_object_class_install_property (object_class, PROP_HIGH_PRIORITY,
    g_param_spec_int ("high-priority", "high priority level",
                      "the GSource priority level to run at",
                      G_MININT, G_MAXINT, 0, G_PARAM_READWRITE |
                      G_PARAM_CONSTRUCT_ONLY | G_PARAM_STATIC_STRINGS));

  g_object_class_install_property (object_class, PROP_LOW_PRIORITY,
    g_param_spec_int ("low-priority", "low priority level",
                      "ignore tasks below this priority level",
                      G_MININT, G_MAXINT, 0, G_PARAM_READWRITE |
                      G_PARAM_CONSTRUCT_ONLY | G_PARAM_STATIC_STRINGS));

  g_type_class_add_private (class, sizeof (GPeriodicPrivate));
}

/**
 * g_periodic_block:
 * @periodic: a #GPeriodic clock
 *
 * Temporarily blocks @periodic from running in order to bring it in
 * synch with an external time source.
 *
 * This function must be called from a handler of the "repair" signal.
 *
 * If this function is called, emission of the tick signal will be
 * suspended until g_periodic_unblock() is called an equal number of
 * times.  Once that happens, the "tick" signal will run immediately and
 * future "tick" signals will be emitted relative to the time at which
 * the last call to g_periodic_unblock() occured.
 *
 * Since: 2.28
 **/
void
g_periodic_block (GPeriodic *periodic)
{
  g_return_if_fail (G_IS_PERIODIC (periodic));
  g_return_if_fail (periodic->priv->in_repair);

  periodic->priv->blocked++;
}

/**
 * g_periodic_unblock:
 * @periodic: a #GPeriodic clock
 * @unblock_time: the unblock time
 *
 * Reverses the effect of a previous call to g_periodic_block().
 *
 * If this call removes the last block, the tick signal is immediately
 * run.  The repair signal may also be run if the clock is marked as
 * damaged.
 *
 * @unblock_time is the monotonic time, as per g_get_monotonic_time(),
 * at which the event causing the unblock occured.
 *
 * This function may not be called from handlers of any signal emitted
 * by @periodic.
 *
 * Since: 2.28
 **/
void
g_periodic_unblock (GPeriodic       *periodic,
                    gint64           unblock_time)
{
  g_return_if_fail (G_IS_PERIODIC (periodic));
  g_return_if_fail (!periodic->priv->in_repair);
  g_return_if_fail (!periodic->priv->in_tick);
  g_return_if_fail (periodic->priv->blocked);

  if (--periodic->priv->blocked)
    {
      periodic->priv->last_run = unblock_time * periodic->priv->hz;
      g_periodic_run (periodic);
    }
}

/**
 * g_periodic_add:
 * @periodic: a #GPeriodic clock
 * @callback: a #GPeriodicTickFunc function
 * @user_data: data for @callback
 * @notify: for freeing @user_data when it is no longer needed
 *
 * Request periodic calls to @callback to start.  The periodicity of the
 * calls is determined by the 'hz' property.
 *
 * This function may not be called from a handler of the repair signal,
 * but it is perfectly reasonable to call it from a handler of the tick
 * signal.
 *
 * The callback may be cancelled later by using g_periodic_remove() on
 * the return value of this function.
 *
 * Returns: a non-zero tag identifying this callback
 *
 * Since: 2.28
 **/
/**
 * GPeriodicTickFunc:
 * @periodic: the #GPeriodic clock that is ticking
 * @timestamp: the timestamp at the time of the tick
 * @user_data: the user data given to g_periodic_add()
 *
 * The signature of the callback function that is called when the
 * #GPeriodic clock ticks.
 *
 * The @timestamp parameter is equal for all callbacks called during a
 * particular tick on a given clock.
 *
 * Since: 2.28
 **/
guint
g_periodic_add (GPeriodic         *periodic,
                GPeriodicTickFunc  callback,
                gpointer           user_data,
                GDestroyNotify     notify)
{
  GPeriodicTick *tick;
  static guint id;

  g_return_val_if_fail (G_IS_PERIODIC (periodic), 0);
  g_return_val_if_fail (!periodic->priv->in_repair, 0);

  tick = g_slice_new (GPeriodicTick);
  tick->callback = callback;
  tick->user_data = user_data;
  tick->notify = notify;
  tick->id = ++id;

  periodic->priv->ticks = g_slist_prepend (periodic->priv->ticks, tick);

  return tick->id;
}

/**
 * g_periodic_remove:
 * @periodic: a #GPeriodic clock
 * @tag: the ID of the callback to remove
 *
 * Reverse the effect of a previous call to g_periodic_start().
 *
 * @tag is the ID returned by that function.
 *
 * This function may not be called from a handler of the repair signal,
 * but it is perfectly reasonable to call it from a handler of the tick
 * signal.
 *
 * Since: 2.28
 **/
void
g_periodic_remove (GPeriodic *periodic,
                   guint      tag)
{
  GSList **iter;

  g_return_if_fail (G_IS_PERIODIC (periodic));
  g_return_if_fail (!periodic->priv->in_repair);

  for (iter = &periodic->priv->ticks; *iter; iter = &(*iter)->next)
    {
      GPeriodicTick *tick = (*iter)->data;

      if (tick->id == tag)
        {
          /* do this first incase the destroy notify re-enters */
          *iter = g_slist_remove (*iter, tick);

          if (tick->notify)
            tick->notify (tick->user_data);

          g_slice_free (GPeriodicTick, tick);
          return;
        }
    }

  g_critical ("GPeriodic: tag %u not registered", tag);
}

/**
 * g_periodic_damaged:
 * @periodic: a #GPeriodic clock
 *
 * Report damage and schedule the "repair" signal to be emitted during
 * the next repair phase.
 *
 * You may not call this function during the repair phase.
 *
 * Since: 2.28
 **/
void
g_periodic_damaged (GPeriodic *periodic)
{
  g_return_if_fail (G_IS_PERIODIC (periodic));
  g_return_if_fail (!periodic->priv->in_repair);

  periodic->priv->damaged = TRUE;
}

/**
 * g_periodic_get_hz:
 * @periodic: a #GPeriodic clock
 *
 * Gets the frequency of the clock.
 *
 * Returns: the frquency of the clock, in Hz
 *
 * Since: 2.28
 **/
guint
g_periodic_get_hz (GPeriodic *periodic)
{
  return periodic->priv->hz;
}

/**
 * g_periodic_get_high_priority:
 * @periodic: a #GPeriodic clock
 *
 * Gets the #GSource priority of the clock.
 *
 * Returns: the high priority level
 *
 * Since: 2.28
 **/
gint
g_periodic_get_high_priority (GPeriodic *periodic)
{
  return g_source_get_priority (periodic->priv->source);
}

/**
 * g_periodic_get_low_priority:
 * @periodic: a #GPeriodic clock
 *
 * Gets the priority level that #GPeriodic uses to check for mainloop
 * inactivity.  Other sources scheduled below this level of priority are
 * effectively ignored by #GPeriodic and may be starved.
 *
 * Returns: the low priority level
 *
 * Since: 2.28
 **/
gint
g_periodic_get_low_priority (GPeriodic *periodic)
{
  return periodic->priv->low_priority;
}

/**
 * g_periodic_new:
 * @hz: the frequency of the new clock in Hz (between 1 and 120)
 * @priority: the #GSource priority to run at
 *
 * Creates a new #GPeriodic clock.
 *
 * The created clock is attached to the thread-default main context in
 * effect at the time of the call to this function.  See
 * g_main_context_push_thread_default() for more information.
 *
 * Due to the fact that #GMainContext is only accurate to the nearest
 * millisecond, the frequency can not meaningfully get too close to
 * 1000.  For this reason, it is arbitrarily bounded at 120.
 *
 * Returns: a new #GPeriodic
 *
 * Since: 2.28
 **/
GPeriodic *
g_periodic_new (guint hz,
                gint  high_priority,
                gint  low_priority)
{
  g_return_val_if_fail (1 <= hz && hz <= 120, NULL);

  return g_object_new (G_TYPE_PERIODIC,
                       "hz", hz,
                       "high-priority", high_priority,
                       "low-priority", low_priority,
                       NULL);
}