gstreamer/gst/gstminiobject.c
Wim Taymans ee235a6b07 miniobject: avoid race in bufferpool release
Avoid playing with the refcount to decide when a buffer has been recycled by the
dispose function. The problem is that we then temporarily can have a buffer with
a refcount > 1 being acquired from the pool, which is not writable. Instead use
a simple boolean return value from the dispose function to inform the called
that the object was recycled or not.
2011-07-25 12:53:10 +02:00

484 lines
13 KiB
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
/* Mutex used for weak referencing */
G_LOCK_DEFINE_STATIC (weak_refs_mutex);
/* 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->flags = 0;
mini_object->size = size;
mini_object->n_weak_refs = 0;
mini_object->weak_refs = NULL;
}
/**
* 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);
}
/**
* 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 {
ret = gst_mini_object_copy (mini_object);
GST_CAT_DEBUG (GST_CAT_PERFORMANCE, "copy %s miniobject %p -> %p",
g_type_name (GST_MINI_OBJECT_TYPE (mini_object)), mini_object, ret);
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: (transfer full): 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);
*/
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;
}
static void
weak_refs_notify (GstMiniObject * obj)
{
guint i;
for (i = 0; i < obj->n_weak_refs; i++)
obj->weak_refs[i].notify (obj->weak_refs[i].data, obj);
g_free (obj->weak_refs);
}
/**
* 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 (mini_object != NULL);
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))) {
gboolean do_free;
if (mini_object->dispose)
do_free = mini_object->dispose (mini_object);
else
do_free = TRUE;
/* if the subclass recycled the object (and returned FALSE) we don't
* want to free the instance anymore */
if (G_LIKELY (do_free)) {
/* The weak reference stack is freed in the notification function */
if (mini_object->n_weak_refs)
weak_refs_notify (mini_object);
#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
*
* Atomically modifies a pointer to point to a new mini-object.
* The reference count of @olddata is decreased and the reference count of
* @newdata is increased.
*
* Either @newdata and the value pointed to by @olddata may be NULL.
*
* Returns: TRUE if @newdata was different from @olddata
*/
gboolean
gst_mini_object_replace (GstMiniObject ** olddata, GstMiniObject * newdata)
{
GstMiniObject *olddata_val;
g_return_val_if_fail (olddata != NULL, FALSE);
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 (G_UNLIKELY (olddata_val == newdata))
return FALSE;
if (newdata)
gst_mini_object_ref (newdata);
while (G_UNLIKELY (!g_atomic_pointer_compare_and_exchange ((gpointer *)
olddata, olddata_val, newdata))) {
olddata_val = g_atomic_pointer_get ((gpointer *) olddata);
if (G_UNLIKELY (olddata_val == newdata))
break;
}
if (olddata_val)
gst_mini_object_unref (olddata_val);
return olddata_val != newdata;
}
/**
* gst_mini_object_steal:
* @olddata: (inout) (transfer full): pointer to a pointer to a mini-object to
* be stolen
*
* Replace the current #GstMiniObject pointer to by @olddata with NULL and
* return the old value.
*
* Returns: the #GstMiniObject at @oldata
*/
GstMiniObject *
gst_mini_object_steal (GstMiniObject ** olddata)
{
GstMiniObject *olddata_val;
g_return_val_if_fail (olddata != NULL, NULL);
GST_CAT_TRACE (GST_CAT_REFCOUNTING, "steal %p (%d)",
*olddata, *olddata ? (*olddata)->refcount : 0);
do {
olddata_val = g_atomic_pointer_get ((gpointer *) olddata);
if (olddata_val == NULL)
break;
} while (G_UNLIKELY (!g_atomic_pointer_compare_and_exchange ((gpointer *)
olddata, olddata_val, NULL)));
return olddata_val;
}
/**
* gst_mini_object_take:
* @olddata: (inout) (transfer full): pointer to a pointer to a mini-object to
* be replaced
*
* Modifies a pointer to point to a new mini-object. The modification
* is done atomically. This version is similar to gst_mini_object_replace()
* except that it does not increase the refcount of @newdata and thus
* takes ownership of @newdata.
*
* Either @newdata and the value pointed to by @olddata may be NULL.
*
* Returns: TRUE if @newdata was different from @olddata
*/
gboolean
gst_mini_object_take (GstMiniObject ** olddata, GstMiniObject * newdata)
{
GstMiniObject *olddata_val;
g_return_val_if_fail (olddata != NULL, FALSE);
GST_CAT_TRACE (GST_CAT_REFCOUNTING, "take %p (%d) with %p (%d)",
*olddata, *olddata ? (*olddata)->refcount : 0,
newdata, newdata ? newdata->refcount : 0);
do {
olddata_val = g_atomic_pointer_get ((gpointer *) olddata);
if (G_UNLIKELY (olddata_val == newdata))
break;
} while (G_UNLIKELY (!g_atomic_pointer_compare_and_exchange ((gpointer *)
olddata, olddata_val, newdata)));
if (olddata_val)
gst_mini_object_unref (olddata_val);
return olddata_val != newdata;
}
/**
* gst_mini_object_weak_ref: (skip)
* @object: #GstMiniObject to reference weakly
* @notify: callback to invoke before the mini object is freed
* @data: extra data to pass to notify
*
* Adds a weak reference callback to a mini object. Weak references are
* used for notification when a mini object is finalized. They are called
* "weak references" because they allow you to safely hold a pointer
* to the mini object without calling gst_mini_object_ref()
* (gst_mini_object_ref() adds a strong reference, that is, forces the object
* to stay alive).
*
* Since: 0.10.35
*/
void
gst_mini_object_weak_ref (GstMiniObject * object,
GstMiniObjectWeakNotify notify, gpointer data)
{
guint i;
g_return_if_fail (object != NULL);
g_return_if_fail (notify != NULL);
g_return_if_fail (GST_MINI_OBJECT_REFCOUNT_VALUE (object) >= 1);
G_LOCK (weak_refs_mutex);
if (object->n_weak_refs) {
/* Don't add the weak reference if it already exists. */
for (i = 0; i < object->n_weak_refs; i++) {
if (object->weak_refs[i].notify == notify &&
object->weak_refs[i].data == data) {
g_warning ("%s: Attempt to re-add existing weak ref %p(%p) failed.",
G_STRFUNC, notify, data);
goto found;
}
}
i = object->n_weak_refs++;
object->weak_refs =
g_realloc (object->weak_refs, sizeof (object->weak_refs[0]) * i);
} else {
object->weak_refs = g_malloc0 (sizeof (object->weak_refs[0]));
object->n_weak_refs = 1;
i = 0;
}
object->weak_refs[i].notify = notify;
object->weak_refs[i].data = data;
found:
G_UNLOCK (weak_refs_mutex);
}
/**
* gst_mini_object_weak_unref: (skip)
* @object: #GstMiniObject to remove a weak reference from
* @notify: callback to search for
* @data: data to search for
*
* Removes a weak reference callback to a mini object.
*
* Since: 0.10.35
*/
void
gst_mini_object_weak_unref (GstMiniObject * object,
GstMiniObjectWeakNotify notify, gpointer data)
{
gboolean found_one = FALSE;
g_return_if_fail (object != NULL);
g_return_if_fail (notify != NULL);
G_LOCK (weak_refs_mutex);
if (object->n_weak_refs) {
guint i;
for (i = 0; i < object->n_weak_refs; i++)
if (object->weak_refs[i].notify == notify &&
object->weak_refs[i].data == data) {
found_one = TRUE;
object->n_weak_refs -= 1;
if (i != object->n_weak_refs)
object->weak_refs[i] = object->weak_refs[object->n_weak_refs];
break;
}
}
G_UNLOCK (weak_refs_mutex);
if (!found_one)
g_warning ("%s: couldn't find weak ref %p(%p)", G_STRFUNC, notify, data);
}