gstreamer/gst/gstminiobject.c

/* GStreamer
 * Copyright (C) 2005 David Schleef <ds@schleef.org>
 *
 * gstminiobject.h: Header for GstMiniObject
 *
 * 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:gstminiobject
 * @short_description: Lightweight base class for the GStreamer object hierarchy
 *
 * #GstMiniObject is a baseclass like #GObject, but has been stripped down of
 * features to be fast and small.
 * It offers sub-classing and ref-counting in the same way as #GObject does.
 * It has no properties and no signal-support though.
 *
 * Last reviewed on 2005-11-23 (0.9.5)
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "gst/gst_private.h"
#include "gst/gstminiobject.h"
#include "gst/gstinfo.h"
#include <gobject/gvaluecollector.h>

#define GST_DISABLE_TRACE

#ifndef GST_DISABLE_TRACE
#include "gsttrace.h"
static GstAllocTrace *_gst_mini_object_trace;
#endif

#define GST_MINI_OBJECT_GET_CLASS_UNCHECKED(obj) \
    ((GstMiniObjectClass *) (((GTypeInstance*)(obj))->g_class))

/* boxed copy and free functions. Don't real copy or free but simply
 * change the refcount */
static GstMiniObject *
_gst_mini_object_boxed_copy (GstMiniObject * mini_object)
{
  if (mini_object)
    return gst_mini_object_ref (mini_object);
  else
    return NULL;
}

static void
_gst_mini_object_boxed_free (GstMiniObject * mini_object)
{
  if (mini_object)
    gst_mini_object_unref (mini_object);
}

/**
 * gst_mini_object_register:
 * @name: name of the new boxed type
 *
 * This function creates a new G_TYPE_BOXED derived type id for a new boxed type
 * with name @name. The default miniobject refcounting copy and free function
 * are used for the boxed type.
 *
 * Returns: a new G_TYPE_BOXED derived type id for @name.
 */
GType
gst_mini_object_register (const gchar * name)
{
  GType type;

  g_return_val_if_fail (name != NULL, 0);

  type = g_boxed_type_register_static (name,
      (GBoxedCopyFunc) _gst_mini_object_boxed_copy,
      (GBoxedFreeFunc) _gst_mini_object_boxed_free);

  return type;
}

/**
 * gst_mini_object_init:
 * @mini_object: a #GstMiniObject 
 * @type: the #GType of the mini-object to create
 * @size: the size of the data
 *
 * Initializes a mini-object with the desired type and size.
 *
 * MT safe
 *
 * Returns: (transfer full): the new mini-object.
 */
void
gst_mini_object_init (GstMiniObject * mini_object, GType type, gsize size)
{
  mini_object->type = type;
  mini_object->refcount = 1;
  mini_object->size = size;
}

/* FIXME 0.11: Current way of doing the copy makes it impossible
 * to currectly chain to the parent classes and do a copy in a
 * subclass without knowing all internals of the parent classes.
 *
 * For 0.11 we should do something like the following:
 *  - The GstMiniObjectClass::copy() implementation of GstMiniObject
 *    should call g_type_create_instance() with the type of the source
 *    object.
 *  - All GstMiniObjectClass::copy() implementations should as first
 *    thing chain up to the parent class and then do whatever they need
 *    to do to copy their type specific data. Note that this way the
 *    instance_init() functions are called!
 */

/**
 * gst_mini_object_copy:
 * @mini_object: the mini-object to copy
 *
 * Creates a copy of the mini-object.
 *
 * MT safe
 *
 * Returns: (transfer full): the new mini-object.
 */
GstMiniObject *
gst_mini_object_copy (const GstMiniObject * mini_object)
{
  GstMiniObject *copy;

  g_return_val_if_fail (mini_object != NULL, NULL);

  if (mini_object->copy)
    copy = mini_object->copy (mini_object);
  else
    copy = NULL;

  return copy;
}

/**
 * gst_mini_object_is_writable:
 * @mini_object: the mini-object to check
 *
 * Checks if a mini-object is writable.  A mini-object is writable
 * if the reference count is one and the #GST_MINI_OBJECT_FLAG_READONLY
 * flag is not set.  Modification of a mini-object should only be
 * done after verifying that it is writable.
 *
 * MT safe
 *
 * Returns: TRUE if the object is writable.
 */
gboolean
gst_mini_object_is_writable (const GstMiniObject * mini_object)
{
  g_return_val_if_fail (mini_object != NULL, FALSE);

  return (GST_MINI_OBJECT_REFCOUNT_VALUE (mini_object) == 1) &&
      ((mini_object->flags & GST_MINI_OBJECT_FLAG_READONLY) == 0);
}

/**
 * gst_mini_object_make_writable:
 * @mini_object: (transfer full): the mini-object to make writable
 *
 * Checks if a mini-object is writable.  If not, a writable copy is made and
 * returned.  This gives away the reference to the original mini object,
 * and returns a reference to the new object.
 *
 * MT safe
 *
 * Returns: (transfer full): a mini-object (possibly the same pointer) that
 *     is writable.
 */
GstMiniObject *
gst_mini_object_make_writable (GstMiniObject * mini_object)
{
  GstMiniObject *ret;

  g_return_val_if_fail (mini_object != NULL, NULL);

  if (gst_mini_object_is_writable (mini_object)) {
    ret = mini_object;
  } else {
    GST_CAT_DEBUG (GST_CAT_PERFORMANCE, "copy %s miniobject",
        g_type_name (G_TYPE_FROM_INSTANCE (mini_object)));
    ret = gst_mini_object_copy (mini_object);
    gst_mini_object_unref (mini_object);
  }

  return ret;
}

/**
 * gst_mini_object_ref:
 * @mini_object: the mini-object
 *
 * Increase the reference count of the mini-object.
 *
 * Note that the refcount affects the writeability
 * of @mini-object, see gst_mini_object_is_writable(). It is
 * important to note that keeping additional references to
 * GstMiniObject instances can potentially increase the number
 * of memcpy operations in a pipeline, especially if the miniobject
 * is a #GstBuffer.
 *
 * Returns: the mini-object.
 */
GstMiniObject *
gst_mini_object_ref (GstMiniObject * mini_object)
{
  g_return_val_if_fail (mini_object != NULL, NULL);
  /* we can't assert that the refcount > 0 since the _free functions
   * increments the refcount from 0 to 1 again to allow resurecting
   * the object
   g_return_val_if_fail (mini_object->refcount > 0, NULL);
   */
  g_return_val_if_fail (GST_IS_MINI_OBJECT (mini_object), NULL);

  GST_CAT_TRACE (GST_CAT_REFCOUNTING, "%p ref %d->%d", mini_object,
      GST_MINI_OBJECT_REFCOUNT_VALUE (mini_object),
      GST_MINI_OBJECT_REFCOUNT_VALUE (mini_object) + 1);

  g_atomic_int_inc (&mini_object->refcount);

  return mini_object;
}

/**
 * gst_mini_object_unref:
 * @mini_object: the mini-object
 *
 * Decreases the reference count of the mini-object, possibly freeing
 * the mini-object.
 */
void
gst_mini_object_unref (GstMiniObject * mini_object)
{
  g_return_if_fail (GST_IS_MINI_OBJECT (mini_object));
  g_return_if_fail (mini_object->refcount > 0);

  GST_CAT_TRACE (GST_CAT_REFCOUNTING, "%p unref %d->%d",
      mini_object,
      GST_MINI_OBJECT_REFCOUNT_VALUE (mini_object),
      GST_MINI_OBJECT_REFCOUNT_VALUE (mini_object) - 1);

  if (G_UNLIKELY (g_atomic_int_dec_and_test (&mini_object->refcount))) {
    /* At this point, the refcount of the object is 0. We increase the refcount
     * here because if a subclass recycles the object and gives out a new
     * reference we don't want to free the instance anymore. */
    gst_mini_object_ref (mini_object);

    if (mini_object->dispose)
      mini_object->dispose (mini_object);

    /* decrement the refcount again, if the subclass recycled the object we don't
     * want to free the instance anymore */
    if (G_LIKELY (g_atomic_int_dec_and_test (&mini_object->refcount))) {
#ifndef GST_DISABLE_TRACE
      gst_alloc_trace_free (_gst_mini_object_trace, mini_object);
#endif
      if (mini_object->free)
        mini_object->free (mini_object);
    }
  }
}

/**
 * gst_mini_object_replace:
 * @olddata: (inout) (transfer full): pointer to a pointer to a mini-object to
 *     be replaced
 * @newdata: pointer to new mini-object
 *
 * Modifies a pointer to point to a new mini-object.  The modification
 * is done atomically, and the reference counts are updated correctly.
 * Either @newdata and the value pointed to by @olddata may be NULL.
 */
void
gst_mini_object_replace (GstMiniObject ** olddata, GstMiniObject * newdata)
{
  GstMiniObject *olddata_val;

  g_return_if_fail (olddata != NULL);

  GST_CAT_TRACE (GST_CAT_REFCOUNTING, "replace %p (%d) with %p (%d)",
      *olddata, *olddata ? (*olddata)->refcount : 0,
      newdata, newdata ? newdata->refcount : 0);

  olddata_val = g_atomic_pointer_get ((gpointer *) olddata);

  if (olddata_val == newdata)
    return;

  if (newdata)
    gst_mini_object_ref (newdata);

  while (!g_atomic_pointer_compare_and_exchange ((gpointer *) olddata,
          olddata_val, newdata)) {
    olddata_val = g_atomic_pointer_get ((gpointer *) olddata);
  }

  if (olddata_val)
    gst_mini_object_unref (olddata_val);
}