gstreamer/gst/gstiterator.c

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/* GStreamer
* Copyright (C) 2004 Wim Taymans <wim@fluendo.com>
*
* gstiterator.h: Base class for iterating datastructures.
*
* 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.
*/
#include "gst_private.h"
#include <gst/gstiterator.h>
static void
gst_iterator_init (GstIterator * it,
GMutex * lock,
guint32 * master_cookie,
GstIteratorNextFunction next,
GstIteratorItemFunction item,
GstIteratorResyncFunction resync, GstIteratorFreeFunction free)
{
it->lock = lock;
it->master_cookie = master_cookie;
it->cookie = *master_cookie;
it->next = next;
it->item = item;
it->resync = resync;
it->free = free;
it->pushed = NULL;
}
/**
* gst_iterator_new:
* @size: the size of the iterator structure
* @lock: pointer to a #GMutex.
* @master_cookie: pointer to a guint32 to protect the iterated object.
* @next: function to get next item
* @item: function to call on each item retrieved
* @resync: function to resync the iterator
* @free: function to free the iterator
*
* Create a new iterator. This function is mainly used for objects
* implementing the next/resync/free function to iterate a data structure.
*
* Returns: the new #GstIterator.
*
* MT safe.
*/
GstIterator *
gst_iterator_new (guint size,
GMutex * lock,
guint32 * master_cookie,
GstIteratorNextFunction next,
GstIteratorItemFunction item,
GstIteratorResyncFunction resync, GstIteratorFreeFunction free)
{
GstIterator *result;
g_return_val_if_fail (size >= sizeof (GstIterator), NULL);
g_return_val_if_fail (master_cookie != NULL, NULL);
g_return_val_if_fail (next != NULL, NULL);
g_return_val_if_fail (resync != NULL, NULL);
g_return_val_if_fail (free != NULL, NULL);
result = g_malloc (size);
gst_iterator_init (result, lock, master_cookie, next, item, resync, free);
return result;
}
More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Original commit message from CVS: * docs/design/part-MT-refcounting.txt: * docs/design/part-conventions.txt: * gst/gstbin.c: (gst_bin_set_index), (gst_bin_set_clock), (gst_bin_add_func), (gst_bin_remove_func), (gst_bin_iterate_elements), (gst_bin_change_state), (gst_bin_dispose), (gst_bin_get_by_name_recurse_up): * gst/gstcaps.c: * gst/gstelement.c: (gst_element_add_pad), (gst_element_remove_pad), (pad_compare_name), (gst_element_get_static_pad), (gst_element_get_request_pad), (gst_element_get_pad), (gst_element_iterate_pads), (gst_element_class_get_pad_template_list), (gst_element_class_get_pad_template), (gst_element_get_random_pad), (gst_element_get_event_masks), (gst_element_send_event), (gst_element_seek), (gst_element_get_query_types), (gst_element_query), (gst_element_get_formats), (gst_element_convert), (gst_element_post_message), (gst_element_set_locked_state), (gst_element_get_state), (gst_element_set_state), (gst_element_pads_activate), (gst_element_dispose), (gst_element_set_manager_func), (gst_element_get_manager): * gst/gstelement.h: * gst/gstiterator.c: (gst_iterator_new), (gst_list_iterator_next), (gst_list_iterator_resync), (gst_list_iterator_free), (gst_iterator_new_list): * gst/gstiterator.h: * gst/gstmessage.c: (_gst_message_copy): * gst/gstobject.c: (gst_object_class_init), (gst_object_init), (gst_object_ref), (gst_object_unref), (gst_object_sink), (gst_object_replace), (gst_object_dispose), (gst_object_dispatch_properties_changed), (gst_object_set_name), (gst_object_set_parent), (gst_object_get_parent), (gst_object_unparent), (gst_object_check_uniqueness), (gst_object_get_path_string): * gst/gstobject.h: * gst/gstpad.c: (gst_pad_dispose), (gst_pad_set_active), (gst_pad_is_active), (gst_pad_set_blocked_async), (gst_pad_is_blocked), (gst_pad_unlink), (gst_pad_is_linked), (gst_pad_link_prepare_filtered), (gst_pad_link_filtered), (gst_pad_get_real_parent), (gst_pad_relink_filtered), (gst_pad_get_peer), (gst_pad_realize), (gst_pad_get_allowed_caps), (gst_pad_alloc_buffer), (gst_pad_push), (gst_pad_pull), (gst_pad_pull_range), (gst_pad_push_event): * gst/gstpad.h: * gst/gstpipeline.c: (gst_pipeline_init), (gst_pipeline_dispose), (is_eos), (pipeline_bus_handler): * gst/gstutils.c: (gst_element_get_compatible_pad_filtered), (gst_element_link_pads_filtered), (gst_element_unlink): * gst/parse/grammar.y: * tools/gst-compprep.c: (main): * tools/gst-inspect.c: (print_pad_info): * tools/gst-launch.c: (main): * tools/gst-xmlinspect.c: (print_element_info): More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Fixed unsafe ghostpad dereffing. Removed old unsafe methods.
2004-12-13 11:33:55 +00:00
/*
* list iterator
*/
typedef struct _GstListIterator
{
GstIterator iterator;
gpointer owner;
GList **orig;
GList *list; /* pointer in list */
GstIteratorDisposeFunction freefunc;
} GstListIterator;
static GstIteratorResult
gst_list_iterator_next (GstListIterator * it, gpointer * elem)
{
if (it->list == NULL)
return GST_ITERATOR_DONE;
*elem = it->list->data;
it->list = g_list_next (it->list);
return GST_ITERATOR_OK;
}
static void
gst_list_iterator_resync (GstListIterator * it)
{
it->list = *it->orig;
}
static void
gst_list_iterator_free (GstListIterator * it)
{
if (it->freefunc) {
it->freefunc (it->owner);
}
g_free (it);
}
/**
* gst_iterator_new_list:
* @lock: pointer to a #GMutex protecting the list.
* @master_cookie: pointer to a guint32 to protect the list.
* @list: pointer to the list
* @owner: object owning the list
* @ref: function to ref each item
* @unref: function to unref each item
* @free: function to free the owner of the list
*
* Create a new iterator designed for iterating @list.
*
* Returns: the new #GstIterator for @list.
*
* MT safe.
*/
More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Original commit message from CVS: * docs/design/part-MT-refcounting.txt: * docs/design/part-conventions.txt: * gst/gstbin.c: (gst_bin_set_index), (gst_bin_set_clock), (gst_bin_add_func), (gst_bin_remove_func), (gst_bin_iterate_elements), (gst_bin_change_state), (gst_bin_dispose), (gst_bin_get_by_name_recurse_up): * gst/gstcaps.c: * gst/gstelement.c: (gst_element_add_pad), (gst_element_remove_pad), (pad_compare_name), (gst_element_get_static_pad), (gst_element_get_request_pad), (gst_element_get_pad), (gst_element_iterate_pads), (gst_element_class_get_pad_template_list), (gst_element_class_get_pad_template), (gst_element_get_random_pad), (gst_element_get_event_masks), (gst_element_send_event), (gst_element_seek), (gst_element_get_query_types), (gst_element_query), (gst_element_get_formats), (gst_element_convert), (gst_element_post_message), (gst_element_set_locked_state), (gst_element_get_state), (gst_element_set_state), (gst_element_pads_activate), (gst_element_dispose), (gst_element_set_manager_func), (gst_element_get_manager): * gst/gstelement.h: * gst/gstiterator.c: (gst_iterator_new), (gst_list_iterator_next), (gst_list_iterator_resync), (gst_list_iterator_free), (gst_iterator_new_list): * gst/gstiterator.h: * gst/gstmessage.c: (_gst_message_copy): * gst/gstobject.c: (gst_object_class_init), (gst_object_init), (gst_object_ref), (gst_object_unref), (gst_object_sink), (gst_object_replace), (gst_object_dispose), (gst_object_dispatch_properties_changed), (gst_object_set_name), (gst_object_set_parent), (gst_object_get_parent), (gst_object_unparent), (gst_object_check_uniqueness), (gst_object_get_path_string): * gst/gstobject.h: * gst/gstpad.c: (gst_pad_dispose), (gst_pad_set_active), (gst_pad_is_active), (gst_pad_set_blocked_async), (gst_pad_is_blocked), (gst_pad_unlink), (gst_pad_is_linked), (gst_pad_link_prepare_filtered), (gst_pad_link_filtered), (gst_pad_get_real_parent), (gst_pad_relink_filtered), (gst_pad_get_peer), (gst_pad_realize), (gst_pad_get_allowed_caps), (gst_pad_alloc_buffer), (gst_pad_push), (gst_pad_pull), (gst_pad_pull_range), (gst_pad_push_event): * gst/gstpad.h: * gst/gstpipeline.c: (gst_pipeline_init), (gst_pipeline_dispose), (is_eos), (pipeline_bus_handler): * gst/gstutils.c: (gst_element_get_compatible_pad_filtered), (gst_element_link_pads_filtered), (gst_element_unlink): * gst/parse/grammar.y: * tools/gst-compprep.c: (main): * tools/gst-inspect.c: (print_pad_info): * tools/gst-launch.c: (main): * tools/gst-xmlinspect.c: (print_element_info): More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Fixed unsafe ghostpad dereffing. Removed old unsafe methods.
2004-12-13 11:33:55 +00:00
GstIterator *
gst_iterator_new_list (GMutex * lock,
guint32 * master_cookie,
GList ** list,
gpointer owner,
GstIteratorItemFunction item, GstIteratorDisposeFunction free)
More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Original commit message from CVS: * docs/design/part-MT-refcounting.txt: * docs/design/part-conventions.txt: * gst/gstbin.c: (gst_bin_set_index), (gst_bin_set_clock), (gst_bin_add_func), (gst_bin_remove_func), (gst_bin_iterate_elements), (gst_bin_change_state), (gst_bin_dispose), (gst_bin_get_by_name_recurse_up): * gst/gstcaps.c: * gst/gstelement.c: (gst_element_add_pad), (gst_element_remove_pad), (pad_compare_name), (gst_element_get_static_pad), (gst_element_get_request_pad), (gst_element_get_pad), (gst_element_iterate_pads), (gst_element_class_get_pad_template_list), (gst_element_class_get_pad_template), (gst_element_get_random_pad), (gst_element_get_event_masks), (gst_element_send_event), (gst_element_seek), (gst_element_get_query_types), (gst_element_query), (gst_element_get_formats), (gst_element_convert), (gst_element_post_message), (gst_element_set_locked_state), (gst_element_get_state), (gst_element_set_state), (gst_element_pads_activate), (gst_element_dispose), (gst_element_set_manager_func), (gst_element_get_manager): * gst/gstelement.h: * gst/gstiterator.c: (gst_iterator_new), (gst_list_iterator_next), (gst_list_iterator_resync), (gst_list_iterator_free), (gst_iterator_new_list): * gst/gstiterator.h: * gst/gstmessage.c: (_gst_message_copy): * gst/gstobject.c: (gst_object_class_init), (gst_object_init), (gst_object_ref), (gst_object_unref), (gst_object_sink), (gst_object_replace), (gst_object_dispose), (gst_object_dispatch_properties_changed), (gst_object_set_name), (gst_object_set_parent), (gst_object_get_parent), (gst_object_unparent), (gst_object_check_uniqueness), (gst_object_get_path_string): * gst/gstobject.h: * gst/gstpad.c: (gst_pad_dispose), (gst_pad_set_active), (gst_pad_is_active), (gst_pad_set_blocked_async), (gst_pad_is_blocked), (gst_pad_unlink), (gst_pad_is_linked), (gst_pad_link_prepare_filtered), (gst_pad_link_filtered), (gst_pad_get_real_parent), (gst_pad_relink_filtered), (gst_pad_get_peer), (gst_pad_realize), (gst_pad_get_allowed_caps), (gst_pad_alloc_buffer), (gst_pad_push), (gst_pad_pull), (gst_pad_pull_range), (gst_pad_push_event): * gst/gstpad.h: * gst/gstpipeline.c: (gst_pipeline_init), (gst_pipeline_dispose), (is_eos), (pipeline_bus_handler): * gst/gstutils.c: (gst_element_get_compatible_pad_filtered), (gst_element_link_pads_filtered), (gst_element_unlink): * gst/parse/grammar.y: * tools/gst-compprep.c: (main): * tools/gst-inspect.c: (print_pad_info): * tools/gst-launch.c: (main): * tools/gst-xmlinspect.c: (print_element_info): More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Fixed unsafe ghostpad dereffing. Removed old unsafe methods.
2004-12-13 11:33:55 +00:00
{
GstListIterator *result;
/* no need to lock, nothing can change here */
result = (GstListIterator *) gst_iterator_new (sizeof (GstListIterator),
lock,
master_cookie,
(GstIteratorNextFunction) gst_list_iterator_next,
(GstIteratorItemFunction) item,
More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Original commit message from CVS: * docs/design/part-MT-refcounting.txt: * docs/design/part-conventions.txt: * gst/gstbin.c: (gst_bin_set_index), (gst_bin_set_clock), (gst_bin_add_func), (gst_bin_remove_func), (gst_bin_iterate_elements), (gst_bin_change_state), (gst_bin_dispose), (gst_bin_get_by_name_recurse_up): * gst/gstcaps.c: * gst/gstelement.c: (gst_element_add_pad), (gst_element_remove_pad), (pad_compare_name), (gst_element_get_static_pad), (gst_element_get_request_pad), (gst_element_get_pad), (gst_element_iterate_pads), (gst_element_class_get_pad_template_list), (gst_element_class_get_pad_template), (gst_element_get_random_pad), (gst_element_get_event_masks), (gst_element_send_event), (gst_element_seek), (gst_element_get_query_types), (gst_element_query), (gst_element_get_formats), (gst_element_convert), (gst_element_post_message), (gst_element_set_locked_state), (gst_element_get_state), (gst_element_set_state), (gst_element_pads_activate), (gst_element_dispose), (gst_element_set_manager_func), (gst_element_get_manager): * gst/gstelement.h: * gst/gstiterator.c: (gst_iterator_new), (gst_list_iterator_next), (gst_list_iterator_resync), (gst_list_iterator_free), (gst_iterator_new_list): * gst/gstiterator.h: * gst/gstmessage.c: (_gst_message_copy): * gst/gstobject.c: (gst_object_class_init), (gst_object_init), (gst_object_ref), (gst_object_unref), (gst_object_sink), (gst_object_replace), (gst_object_dispose), (gst_object_dispatch_properties_changed), (gst_object_set_name), (gst_object_set_parent), (gst_object_get_parent), (gst_object_unparent), (gst_object_check_uniqueness), (gst_object_get_path_string): * gst/gstobject.h: * gst/gstpad.c: (gst_pad_dispose), (gst_pad_set_active), (gst_pad_is_active), (gst_pad_set_blocked_async), (gst_pad_is_blocked), (gst_pad_unlink), (gst_pad_is_linked), (gst_pad_link_prepare_filtered), (gst_pad_link_filtered), (gst_pad_get_real_parent), (gst_pad_relink_filtered), (gst_pad_get_peer), (gst_pad_realize), (gst_pad_get_allowed_caps), (gst_pad_alloc_buffer), (gst_pad_push), (gst_pad_pull), (gst_pad_pull_range), (gst_pad_push_event): * gst/gstpad.h: * gst/gstpipeline.c: (gst_pipeline_init), (gst_pipeline_dispose), (is_eos), (pipeline_bus_handler): * gst/gstutils.c: (gst_element_get_compatible_pad_filtered), (gst_element_link_pads_filtered), (gst_element_unlink): * gst/parse/grammar.y: * tools/gst-compprep.c: (main): * tools/gst-inspect.c: (print_pad_info): * tools/gst-launch.c: (main): * tools/gst-xmlinspect.c: (print_element_info): More MT fixes, added design document describing refcounting policies used in GStreamer and locking involved. Fixed unsafe ghostpad dereffing. Removed old unsafe methods.
2004-12-13 11:33:55 +00:00
(GstIteratorResyncFunction) gst_list_iterator_resync,
(GstIteratorFreeFunction) gst_list_iterator_free);
result->owner = owner;
result->orig = list;
result->list = *list;
result->freefunc = free;
return GST_ITERATOR (result);
}
static void
gst_iterator_pop (GstIterator * it)
{
if (it->pushed) {
gst_iterator_free (it->pushed);
it->pushed = NULL;
}
}
/**
* gst_iterator_next:
* @it: The #GstIterator to iterate
* @elem: pointer to hold next element
*
* Get the next item from the iterator.
*
* Returns: The result of the iteration.
*
* MT safe.
*/
GstIteratorResult
gst_iterator_next (GstIterator * it, gpointer * elem)
{
GstIteratorResult result;
g_return_val_if_fail (it != NULL, GST_ITERATOR_ERROR);
g_return_val_if_fail (elem != NULL, GST_ITERATOR_ERROR);
restart:
if (it->pushed) {
result = gst_iterator_next (it->pushed, elem);
if (result == GST_ITERATOR_DONE) {
/* we are done with this iterator, pop it and
* fallthrough iterating the main iterator again. */
gst_iterator_pop (it);
} else {
return result;
}
}
if (G_LIKELY (it->lock))
g_mutex_lock (it->lock);
if (G_UNLIKELY (*it->master_cookie != it->cookie)) {
result = GST_ITERATOR_RESYNC;
goto done;
}
result = it->next (it, elem);
if (it->item) {
GstIteratorItem itemres;
itemres = it->item (it, *elem);
switch (itemres) {
case GST_ITERATOR_ITEM_SKIP:
if (G_LIKELY (it->lock))
g_mutex_unlock (it->lock);
goto restart;
case GST_ITERATOR_ITEM_END:
result = GST_ITERATOR_DONE;
break;
case GST_ITERATOR_ITEM_PASS:
break;
}
}
done:
if (G_LIKELY (it->lock))
g_mutex_unlock (it->lock);
return result;
}
/**
* gst_iterator_resync:
* @it: The #GstIterator to resync
*
* Resync the iterator. this function is mostly called
* after #gst_iterator_next() returned #GST_ITERATOR_RESYNC.
*
* MT safe.
*/
void
gst_iterator_resync (GstIterator * it)
{
g_return_if_fail (it != NULL);
gst_iterator_pop (it);
if (G_LIKELY (it->lock))
g_mutex_lock (it->lock);
it->resync (it);
it->cookie = *it->master_cookie;
if (G_LIKELY (it->lock))
g_mutex_unlock (it->lock);
}
/**
* gst_iterator_free:
* @it: The #GstIterator to free
*
* Free the iterator.
*
* MT safe.
*/
void
gst_iterator_free (GstIterator * it)
{
g_return_if_fail (it != NULL);
gst_iterator_pop (it);
it->free (it);
}
/**
* gst_iterator_push:
* @it: The #GstIterator to use
* @other: The #GstIterator to push
*
* Pushes @other iterator onto @it. All calls performed on @it are
* forwarded tot @other. If @other returns #GST_ITERATOR_DONE, it is
* popped again and calls are handled by @it again.
*
* This function is mainly used by objects implementing the iterator
* next function to recurse into substructures.
*
* MT safe.
*/
void
gst_iterator_push (GstIterator * it, GstIterator * other)
{
g_return_if_fail (it != NULL);
g_return_if_fail (other != NULL);
it->pushed = other;
}
typedef struct _GstIteratorFilter
{
GstIterator iterator;
GstIterator *slave;
GCompareFunc func;
gpointer user_data;
gboolean compare;
gboolean first;
gboolean found;
} GstIteratorFilter;
/* this function can iterate in 3 modes:
* filter, foreach and find_custom.
*/
static GstIteratorResult
filter_next (GstIteratorFilter * it, gpointer * elem)
{
GstIteratorResult result;
gboolean done = FALSE;
*elem = NULL;
if (G_UNLIKELY (it->found))
return GST_ITERATOR_DONE;
while (G_LIKELY (!done)) {
gpointer item;
result = gst_iterator_next (it->slave, &item);
switch (result) {
case GST_ITERATOR_OK:
if (G_LIKELY (GST_ITERATOR (it)->lock))
g_mutex_unlock (GST_ITERATOR (it)->lock);
if (it->compare) {
if (it->func (item, it->user_data) == 0) {
*elem = item;
done = TRUE;
if (it->first)
it->found = TRUE;
}
} else {
it->func (item, it->user_data);
}
if (G_LIKELY (GST_ITERATOR (it)->lock))
g_mutex_lock (GST_ITERATOR (it)->lock);
break;
case GST_ITERATOR_RESYNC:
case GST_ITERATOR_DONE:
done = TRUE;
break;
default:
g_assert_not_reached ();
break;
}
}
return result;
}
static void
filter_resync (GstIteratorFilter * it)
{
gst_iterator_resync (it->slave);
it->found = FALSE;
}
static void
filter_uninit (GstIteratorFilter * it)
{
it->slave->lock = GST_ITERATOR (it)->lock;
}
static void
filter_free (GstIteratorFilter * it)
{
filter_uninit (it);
gst_iterator_free (it->slave);
g_free (it);
}
/**
* gst_iterator_filter:
* @it: The #GstIterator to filter
* @user_data: user data passed to the compare function
* @func: the compare function to select elements
*
* Create a new iterator from an existing iterator. The new iterator
* will only return those elements that match the given compare function.
* The GCompareFunc should return 0 for elements that should be included
* in the iterator.
*
* When this iterator is freed, @it will also be freed.
*
* Returns: a new #GstIterator.
*
* MT safe.
*/
GstIterator *
gst_iterator_filter (GstIterator * it, gpointer user_data, GCompareFunc func)
{
GstIteratorFilter *result;
g_return_val_if_fail (it != NULL, NULL);
g_return_val_if_fail (func != NULL, NULL);
result = (GstIteratorFilter *) gst_iterator_new (sizeof (GstIteratorFilter),
it->lock, it->master_cookie,
(GstIteratorNextFunction) filter_next,
(GstIteratorItemFunction) NULL,
(GstIteratorResyncFunction) filter_resync,
(GstIteratorFreeFunction) filter_free);
it->lock = NULL;
result->func = func;
result->user_data = user_data;
result->slave = it;
result->compare = TRUE;
result->first = FALSE;
result->found = FALSE;
return GST_ITERATOR (result);
}
/**
* gst_iterator_foreach:
* @it: The #GstIterator to iterate
* @function: the function to call for each element.
* @user_data: user data passed to the function
*
* Iterate over all element of @it and call the given function for
* each element.
*
* MT safe.
*/
void
gst_iterator_foreach (GstIterator * it, GFunc function, gpointer user_data)
{
GstIteratorFilter filter;
gpointer dummy;
g_return_if_fail (it != NULL);
g_return_if_fail (function != NULL);
gst_iterator_init (GST_ITERATOR (&filter),
it->lock, it->master_cookie,
(GstIteratorNextFunction) filter_next,
(GstIteratorItemFunction) NULL,
(GstIteratorResyncFunction) filter_resync,
(GstIteratorFreeFunction) filter_uninit);
it->lock = NULL;
filter.func = (GCompareFunc) function;
filter.user_data = user_data;
filter.slave = it;
filter.compare = FALSE;
filter.first = FALSE;
filter.found = FALSE;
gst_iterator_next (GST_ITERATOR (&filter), &dummy);
gst_iterator_free (GST_ITERATOR (&filter));
}
/**
* gst_iterator_find_custom:
* @it: The #GstIterator to iterate
* @user_data: user data passed to the compare function
* @func: the compare function to use
*
* Find the first element in @it that matches the compare function.
* The compare function should return 0 when the element is found.
*
* Returns: The element in the iterator that matches the compare
* function or NULL when no element matched.
*
* MT safe.
*/
gpointer
gst_iterator_find_custom (GstIterator * it, gpointer user_data,
GCompareFunc func)
{
GstIteratorFilter filter;
gpointer result = NULL;
g_return_val_if_fail (it != NULL, NULL);
g_return_val_if_fail (func != NULL, NULL);
gst_iterator_init (GST_ITERATOR (&filter),
it->lock, it->master_cookie,
(GstIteratorNextFunction) filter_next,
(GstIteratorItemFunction) NULL,
(GstIteratorResyncFunction) filter_resync,
(GstIteratorFreeFunction) filter_uninit);
it->lock = NULL;
filter.func = func;
filter.user_data = user_data;
filter.slave = it;
filter.compare = TRUE;
filter.first = TRUE;
filter.found = FALSE;
gst_iterator_next (GST_ITERATOR (&filter), &result);
gst_iterator_free (GST_ITERATOR (&filter));
return result;
}