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GStreamer 0.10 Core Reference Manual | ![]() |
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#include <gst/gst.h> GstIterator; enum GstIteratorItem; enum GstIteratorResult; void (*GstIteratorDisposeFunction) (gpointer owner); GstIteratorResult (*GstIteratorNextFunction) (GstIterator *it, gpointer *result); GstIteratorItem (*GstIteratorItemFunction) (GstIterator *it, gpointer item); void (*GstIteratorResyncFunction) (GstIterator *it); void (*GstIteratorFreeFunction) (GstIterator *it); gboolean (*GstIteratorFoldFunction) (gpointer item, GValue *ret, gpointer user_data); gpointer (*GstCopyFunction) (gpointer object); #define GST_ITERATOR (it) #define GST_ITERATOR_LOCK (it) #define GST_ITERATOR_COOKIE (it) #define GST_ITERATOR_ORIG_COOKIE (it) GstIterator* gst_iterator_new (guint size, GType type, GMutex *lock, guint32 *master_cookie, GstIteratorNextFunction next, GstIteratorItemFunction item, GstIteratorResyncFunction resync, GstIteratorFreeFunction free); GstIterator* gst_iterator_new_list (GType type, GMutex *lock, guint32 *master_cookie, GList **list, gpointer owner, GstIteratorItemFunction item, GstIteratorDisposeFunction free); GstIterator* gst_iterator_new_single (GType type, gpointer object, GstCopyFunction copy, GFreeFunc free); GstIteratorResult gst_iterator_next (GstIterator *it, gpointer *elem); void gst_iterator_resync (GstIterator *it); void gst_iterator_free (GstIterator *it); void gst_iterator_push (GstIterator *it, GstIterator *other); GstIterator* gst_iterator_filter (GstIterator *it, GCompareFunc func, gpointer user_data); GstIteratorResult gst_iterator_fold (GstIterator *it, GstIteratorFoldFunction func, GValue *ret, gpointer user_data); GstIteratorResult gst_iterator_foreach (GstIterator *it, GFunc func, gpointer user_data); gpointer gst_iterator_find_custom (GstIterator *it, GCompareFunc func, gpointer user_data);
A GstIterator is used to retrieve multiple objects from another object in a threadsafe way.
Various GStreamer objects provide access to their internal structures using an iterator.
In general, whenever calling a GstIterator function results in your code receiving a refcounted object, the refcount for that object will have been increased. Your code is responsible for unrefing that object after use.
The basic use pattern of an iterator is as follows:
Example 13. Using an iterator
it = _get_iterator(object); done = FALSE; while (!done) { switch (gst_iterator_next (it, &item)) { case GST_ITERATOR_OK: ... use/change item here... gst_object_unref (item); break; case GST_ITERATOR_RESYNC: ...rollback changes to items... gst_iterator_resync (it); break; case GST_ITERATOR_ERROR: ...wrong parameters were given... done = TRUE; break; case GST_ITERATOR_DONE: done = TRUE; break; } } gst_iterator_free (it);
Last reviewed on 2009-06-16 (0.10.24)
typedef struct { } GstIterator;
GstIterator base structure. The values of this structure are protected for subclasses, use the methods to use the GstIterator.
typedef enum { GST_ITERATOR_ITEM_SKIP = 0, GST_ITERATOR_ITEM_PASS = 1, GST_ITERATOR_ITEM_END = 2 } GstIteratorItem;
The result of a GstIteratorItemFunction.
typedef enum { GST_ITERATOR_DONE = 0, GST_ITERATOR_OK = 1, GST_ITERATOR_RESYNC = 2, GST_ITERATOR_ERROR = 3 } GstIteratorResult;
The result of gst_iterator_next()
.
void (*GstIteratorDisposeFunction) (gpointer owner);
The function that will be called when a GList iterator is freed. The owner of the GList iterator can then clean up its resources.
owner : |
the owner of the iterator |
GstIteratorResult (*GstIteratorNextFunction) (GstIterator *it, gpointer *result);
The function that will be called when the next element of the iterator should be retrieved.
Implementors of a GstIterator should implement this function and pass it to the constructor of the custom iterator. The function will be called with the iterator lock held.
it : |
the iterator |
result : |
a pointer to hold the next item |
Returns : | the result of the operation. |
GstIteratorItem (*GstIteratorItemFunction) (GstIterator *it, gpointer item);
The function that will be called after the next item of the iterator has been retrieved. This function will typically increase the refcount of the item or make a copy.
Implementors of a GstIterator should implement this function and pass it to the constructor of the custom iterator. The function will be called with the iterator lock held.
it : |
the iterator |
item : |
the item being retrieved. |
Returns : | the result of the operation. |
void (*GstIteratorResyncFunction) (GstIterator *it);
This function will be called whenever a concurrent update happened to the iterated datastructure. The implementor of the iterator should restart the iterator from the beginning and clean up any state it might have.
Implementors of a GstIterator should implement this function and pass it to the constructor of the custom iterator. The function will be called with the iterator lock held.
it : |
the iterator |
void (*GstIteratorFreeFunction) (GstIterator *it);
This function will be called when the iterator is freed.
Implementors of a GstIterator should implement this function and pass it to the constructor of the custom iterator. The function will be called with the iterator lock held.
it : |
the iterator |
gboolean (*GstIteratorFoldFunction) (gpointer item, GValue *ret, gpointer user_data);
A function to be passed to gst_iterator_fold()
.
item : |
the item to fold |
ret : |
a GValue collecting the result |
user_data : |
data passed to gst_iterator_fold()
|
Returns : | TRUE if the fold should continue, FALSE if it should stop. |
gpointer (*GstCopyFunction) (gpointer object);
A function to create a copy of some object or increase its reference count.
object : |
The object to copy |
Returns : | a copy of the object or the same object with increased reference count |
Since 0.10.25
#define GST_ITERATOR(it) ((GstIterator*)(it))
Macro to cast to a GstIterator
it : |
the GstIterator value |
#define GST_ITERATOR_LOCK(it) (GST_ITERATOR(it)->lock)
Macro to get the lock protecting the datastructure being iterated.
it : |
the GstIterator to get the lock of |
#define GST_ITERATOR_COOKIE(it) (GST_ITERATOR(it)->cookie)
Macro to get the cookie of a GstIterator. The cookie of the iterator is the value of the master cookie when the iterator was created. Whenever the iterator is iterated, the value is compared to the value of the master cookie. If they are different, a concurrent modification happened to the iterator and a resync is needed.
it : |
the GstIterator to get the cookie of |
#define GST_ITERATOR_ORIG_COOKIE(it) (GST_ITERATOR(it)->master_cookie)
Macro to get a pointer to where the master cookie is stored. The master cookie protects the structure being iterated and gets updated whenever the datastructure changes.
it : |
the GstIterator to get the master cookie of |
GstIterator* gst_iterator_new (guint size, GType type, GMutex *lock, guint32 *master_cookie, GstIteratorNextFunction next, GstIteratorItemFunction item, GstIteratorResyncFunction resync, GstIteratorFreeFunction free);
Create a new iterator. This function is mainly used for objects implementing the next/resync/free function to iterate a data structure.
For each item retrieved, the item
function is called with the lock
held. The free
function is called when the iterator is freed.
size : |
the size of the iterator structure |
type : |
GType of children |
lock : |
pointer to a GMutex. |
master_cookie : |
pointer to a guint32 that is changed when the items in the iterator changed. |
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 |
Returns : | the new GstIterator. MT safe. |
GstIterator* gst_iterator_new_list (GType type, GMutex *lock, guint32 *master_cookie, GList **list, gpointer owner, GstIteratorItemFunction item, GstIteratorDisposeFunction free);
Create a new iterator designed for iterating list
.
The list you iterate is usually part of a data structure owner
and is
protected with lock
.
The iterator will use lock
to retrieve the next item of the list and it
will then call the item
function before releasing lock
again.
The item
function usualy makes sure that the item remains alive while
lock
is released and the application is using the item. The application is
responsible for freeing/unreffing the item after usage as explained in
gst_iterator_next()
.
When a concurrent update to the list is performed, usually by owner
while
holding lock
, master_cookie
will be updated. The iterator implementation
will notice the update of the cookie and will return GST_ITERATOR_RESYNC
to
the user of the iterator in the next call to gst_iterator_next()
.
owner
will be passed to the free
function when the iterator is freed.
type : |
GType of elements |
lock : |
pointer to a GMutex protecting the list. |
master_cookie : |
pointer to a guint32 that is incremented when the list is changed. |
list : |
pointer to the list |
owner : |
object owning the list |
item : |
function to call for each item |
free : |
function to call when the iterator is freed |
Returns : | the new GstIterator for list .
MT safe.
|
GstIterator* gst_iterator_new_single (GType type, gpointer object, GstCopyFunction copy, GFreeFunc free);
This GstIterator is a convenient iterator for the common case where a GstIterator needs to be returned but only a single object has the be considered. This happens often for the GstPadIterIntLinkFunction.
type : |
GType of the passed object |
object : |
object that this iterator should return |
copy : |
Function that returns a copy of object or increases its refcount
|
free : |
Function to be called for freeing object
|
Returns : | the new GstIterator for object .
|
Since 0.10.25
GstIteratorResult gst_iterator_next (GstIterator *it, gpointer *elem);
Get the next item from the iterator in elem
.
Only when this function returns GST_ITERATOR_OK
, elem
will contain a valid
value. For iterators that return refcounted objects, the returned object
will have its refcount increased and should therefore be unreffed after
usage.
When this function returns GST_ITERATOR_DONE
, no more elements can be
retrieved from it
.
A return value of GST_ITERATOR_RESYNC
indicates that the element list was
concurrently updated. The user of it
should call gst_iterator_resync()
to
get the newly updated list.
A return value of GST_ITERATOR_ERROR
indicates an unrecoverable fatal error.
it : |
The GstIterator to iterate |
elem : |
pointer to hold next element |
Returns : | The result of the iteration. Unref elem after usage if this
is a refcounted object.
MT safe.
|
void gst_iterator_resync (GstIterator *it);
Resync the iterator. this function is mostly called
after gst_iterator_next()
returned GST_ITERATOR_RESYNC
.
When an iterator was pushed on it
, it will automatically be popped again
with this function.
MT safe.
it : |
The GstIterator to resync |
void gst_iterator_free (GstIterator *it);
Free the iterator.
MT safe.
it : |
The GstIterator to free |
void gst_iterator_push (GstIterator *it, GstIterator *other);
Pushes other
iterator onto it
. All calls performed on it
are
forwarded to 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.
When gst_iterator_resync()
is called on it
, other
will automatically be
popped.
MT safe.
it : |
The GstIterator to use |
other : |
The GstIterator to push |
GstIterator* gst_iterator_filter (GstIterator *it, GCompareFunc func, gpointer user_data);
Create a new iterator from an existing iterator. The new iterator
will only return those elements that match the given compare function func
.
func
should return 0 for elements that should be included
in the iterator.
When this iterator is freed, it
will also be freed.
it : |
The GstIterator to filter |
func : |
the compare function to select elements |
user_data : |
user data passed to the compare function |
Returns : | a new GstIterator. MT safe. |
GstIteratorResult gst_iterator_fold (GstIterator *it, GstIteratorFoldFunction func, GValue *ret, gpointer user_data);
Folds func
over the elements of iter
. That is to say, func
will be called
as func
(object, ret
, user_data
) for each object in it
. The normal use
of this procedure is to accumulate the results of operating on the objects in
ret
. If object is a refcounted object its refcount will be increased
before func
is called, and it should be unrefed after use in func
.
This procedure can be used (and is used internally) to implement the
gst_iterator_foreach()
and gst_iterator_find_custom()
operations.
The fold will proceed as long as func
returns TRUE. When the iterator has no
more arguments, GST_ITERATOR_DONE
will be returned. If func
returns FALSE,
the fold will stop, and GST_ITERATOR_OK
will be returned. Errors or resyncs
will cause fold to return GST_ITERATOR_ERROR
or GST_ITERATOR_RESYNC
as
appropriate.
The iterator will not be freed.
it : |
The GstIterator to fold over |
func : |
the fold function |
ret : |
the seed value passed to the fold function |
user_data : |
user data passed to the fold function |
Returns : | A GstIteratorResult, as described above. MT safe. |
GstIteratorResult gst_iterator_foreach (GstIterator *it, GFunc func, gpointer user_data);
Iterate over all element of it
and call the given function func
for
each element. As in gst_iterator_fold()
, the refcount of a refcounted
object will be increased before func
is called, and should be unrefed
after use.
it : |
The GstIterator to iterate |
func : |
the function to call for each element. |
user_data : |
user data passed to the function |
Returns : | the result call to gst_iterator_fold() . The iterator will not be
freed.
MT safe.
|
gpointer gst_iterator_find_custom (GstIterator *it, GCompareFunc func, gpointer user_data);
Find the first element in it
that matches the compare function func
.
func
should return 0 when the element is found. As in gst_iterator_fold()
,
the refcount of a refcounted object will be increased before func
is
called, and should be unrefed after use.
The iterator will not be freed.
This function will return NULL if an error or resync happened to the iterator.
it : |
The GstIterator to iterate |
func : |
the compare function to use |
user_data : |
user data passed to the compare function |
Returns : | The element in the iterator that matches the compare function or NULL when no element matched. MT safe. |