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GStreamer 0.9 Core Reference Manual | ![]() |
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GstObjectGstObject — Base class for the GStreamer object hierarchy |
#include <gst/gst.h> GstObject; enum GstObjectFlags; #define GST_OBJECT_FLAGS (obj) #define GST_OBJECT_FLAG_IS_SET (obj,flag) #define GST_OBJECT_FLAG_SET (obj,flag) #define GST_OBJECT_FLAG_UNSET (obj,flag) #define GST_OBJECT_NAME (obj) #define GST_OBJECT_PARENT (obj) #define GST_LOCK (obj) #define GST_TRYLOCK (obj) #define GST_UNLOCK (obj) #define GST_GET_LOCK (obj) #define GST_OBJECT_IS_DISPOSING (obj) #define GST_OBJECT_IS_FLOATING (obj) #define GST_OBJECT_REFCOUNT (obj) #define GST_OBJECT_REFCOUNT_VALUE (obj) #define GST_CLASS_GET_LOCK (obj) #define GST_CLASS_LOCK (obj) #define GST_CLASS_TRYLOCK (obj) #define GST_CLASS_UNLOCK (obj) gboolean gst_object_set_name (GstObject *object, const gchar *name); gchar* gst_object_get_name (GstObject *object); gboolean gst_object_set_parent (GstObject *object, GstObject *parent); GstObject* gst_object_get_parent (GstObject *object); void gst_object_unparent (GstObject *object); gchar* gst_object_get_name_prefix (GstObject *object); void gst_object_set_name_prefix (GstObject *object, const gchar *name_prefix); void gst_object_default_deep_notify (GObject *object, GstObject *orig, GParamSpec *pspec, gchar **excluded_props); void gst_object_default_error (GstObject *source, GError *error, gchar *debug); gboolean gst_object_check_uniqueness (GList *list, const gchar *name); gboolean gst_object_has_ancestor (GstObject *object, GstObject *ancestor); xmlNodePtr gst_object_save_thyself (GstObject *object, xmlNodePtr parent); void gst_object_restore_thyself (GstObject *object, xmlNodePtr self); gpointer gst_object_ref (gpointer object); void gst_object_unref (gpointer object); void gst_object_sink (gpointer object); void gst_object_replace (GstObject **oldobj, GstObject *newobj); gchar* gst_object_get_path_string (GstObject *object); guint gst_class_signal_connect (GstObjectClass *klass, const gchar *name, gpointer func, gpointer func_data); void gst_class_signal_emit_by_name (GstObject *object, const gchar *name, xmlNodePtr self);
GObject +----GstObject +----GstPad +----GstPluginFeature +----GstElement +----GstPlugin +----GstRegistry +----GstPadTemplate +----GstBus +----GstClock +----GstIndex +----GstTask +----GstXML +----GstCollectPads
"deep-notify" void user_function (GstObject *gstobject, GObject *prop_object, GParamSpec *prop, gpointer user_data); "object-saved" void user_function (GstObject *gstobject, gpointer xml_node, gpointer user_data); "parent-set" void user_function (GstObject *gstobject, GObject *parent, gpointer user_data); "parent-unset" void user_function (GstObject *gstobject, GObject *parent, gpointer user_data);
GstObject provides a root for the object hierarchy tree filed in by the GST library. It is currently a thin wrapper on top of GObject. It is an abstract class that is not very usable on its own.
GstObject gives us basic refcounting, parenting functionality and locking.
Most of the function are just extended for special gstreamer needs and can be
found under the same name in the base class of GstObject which is GObject
(e.g. g_object_ref()
becomes gst_object_ref()
).
The most interesting difference between GstObject and GObject is the
"floating" reference count. A GObject is created with a reference count of
1, owned by the creator of the GObject. (The owner of a reference is the
code section that has the right to call gst_object_unref()
in order to
remove that reference.) A GstObject is created with a reference count of 1
also, but it isn't owned by anyone; calling gst_object_unref()
on the
newly-created GtkObject is incorrect. Instead, the initial reference count
of a GstObject is "floating". The floating reference can be removed by
anyone at any time, by calling gst_object_sink()
. gst_object_sink()
does
nothing if an object is already sunk (has no floating reference).
When you add a GstElement to its parent container, the parent container will do this:
gst_object_ref (GST_OBJECT (child_element)); gst_object_sink (GST_OBJECT (child_element));
This means that the container now owns a reference to the child element
(since it called gst_object_ref()
), and the child element has no floating
reference.
The purpose of the floating reference is to keep the child element alive until you add it to a parent container:
element = gst_element_factory_make (factoryname, name); // element has one floating reference to keep it alive gst_bin_add (GST_BIN (bin), element); // element has one non-floating reference owned by the container
Another effect of this is, that calling gst_object_unref()
on a bin object,
will also destoy all the GstElement objects in it. The same is true for
calling gst_bin_remove()
.
In contrast to GObject instances GstObject add a name property. The functions
gst_object_set_name()
and gst_object_get_name()
are used to set/get the name
of the object.
typedef struct { gint refcount; GMutex *lock; /* object LOCK */ gchar *name; /* object name */ gchar *name_prefix; /* used for debugging */ GstObject *parent; /* this object's parent, weak ref */ guint32 flags; } GstObject;
GStreamer base object class.
typedef enum { GST_OBJECT_DISPOSING = (1<<0), GST_OBJECT_FLOATING = (1<<1), /* padding */ GST_OBJECT_FLAG_LAST = (1<<4) } GstObjectFlags;
The standard flags that an gstobject may have.
GST_OBJECT_DISPOSING |
the object is been destroyed, do use it anymore |
GST_OBJECT_FLOATING |
the object has a floating reference count (e.g. its not assigned to a bin) |
GST_OBJECT_FLAG_LAST |
subclasses can add additional flags starting from this flag |
#define GST_OBJECT_FLAGS(obj) (GST_OBJECT_CAST (obj)->flags)
This macro returns the entire set of flags for the object.
obj : |
Object to return flags for. |
#define GST_OBJECT_FLAG_IS_SET(obj,flag) (GST_OBJECT_FLAGS (obj) & (flag))
This macro checks to see if the given flag is set.
obj : |
Object to check for flags. |
flag : |
Flag to check for |
#define GST_OBJECT_FLAG_SET(obj,flag) (GST_OBJECT_FLAGS (obj) |= (flag))
This macro sets the given bits.
obj : |
Object to set flag in. |
flag : |
Flag to set |
#define GST_OBJECT_FLAG_UNSET(obj,flag) (GST_OBJECT_FLAGS (obj) &= ~(flag))
This macro usets the given bits.
obj : |
Object to unset flag in. |
flag : |
Flag to set |
#define GST_OBJECT_NAME(obj) (GST_OBJECT_CAST(obj)->name)
Get the name of this object
obj : |
Object to get the name of. |
#define GST_OBJECT_PARENT(obj) (GST_OBJECT_CAST(obj)->parent)
Get the parent of this object
obj : |
Object to get the parent of. |
#define GST_LOCK(obj) g_mutex_lock(GST_OBJECT_CAST(obj)->lock)
Acquire a reference to the mutex of this object.
obj : |
Object to get the mutex of. |
#define GST_TRYLOCK(obj) g_mutex_trylock(GST_OBJECT_CAST(obj)->lock)
This macro will try to obtain a lock on the object, but will return with FALSE if it can't get it immediately.
obj : |
Object to try to get a lock on. |
#define GST_OBJECT_IS_DISPOSING(obj) (GST_OBJECT_FLAG_IS_SET (obj, GST_OBJECT_DISPOSING))
Check if the given object is beeing destroyed.
obj : |
Object to check |
#define GST_OBJECT_IS_FLOATING(obj) (GST_OBJECT_FLAG_IS_SET (obj, GST_OBJECT_FLOATING))
Check if the given object is floating (has no owner).
obj : |
Object to check |
#define GST_OBJECT_REFCOUNT(obj)
Get access to the reference count field of the object.
obj : |
Object get the refcount for. |
#define GST_OBJECT_REFCOUNT_VALUE(obj)
Get the reference count value of the object.
obj : |
Object get the refcount value for. |
#define GST_CLASS_LOCK(obj) (g_static_rec_mutex_lock(GST_OBJECT_CLASS_CAST(obj)->lock))
obj : |
#define GST_CLASS_TRYLOCK(obj) (g_static_rec_mutex_trylock(GST_OBJECT_CLASS_CAST(obj)->lock))
obj : |
#define GST_CLASS_UNLOCK(obj) (g_static_rec_mutex_unlock(GST_OBJECT_CLASS_CAST(obj)->lock))
obj : |
gboolean gst_object_set_name (GstObject *object, const gchar *name);
Sets the name of the object, or gives the object a guaranteed unique
name (if name
is NULL).
This function makes a copy of the provided name, so the caller
retains ownership of the name it sent.
object : |
a GstObject to set the name of |
name : |
new name of object |
Returns : | TRUE if the name could be set. Objects that have a parent cannot be renamed. MT safe. This function grabs and releases the object's LOCK. |
gchar* gst_object_get_name (GstObject *object);
Returns a copy of the name of the object.
Caller should g_free()
the return value after usage.
For a nameless object, this returns NULL, which you can safely g_free()
as well.
gboolean gst_object_set_parent (GstObject *object, GstObject *parent);
Sets the parent of object
. The object's reference count will be incremented,
and any floating reference will be removed (see gst_object_sink()
).
Causes the parent-set signal to be emitted.
object : |
GstObject to set parent of |
parent : |
new parent of object |
Returns : | TRUE if the parent could be set or FALSE when the object already had a parent, the object and parent are the same or wrong parameters were provided. MT safe. Grabs and releases the object's LOCK. |
GstObject* gst_object_get_parent (GstObject *object);
Returns the parent of object
. This function increases the refcount
of the parent object so you should gst_object_unref()
it after usage.
object : |
GstObject to get parent of |
Returns : | parent of the object, this can be NULL if the object has no parent. unref after usage. MT safe. Grabs and releases the object's LOCK. |
void gst_object_unparent (GstObject *object);
Clear the parent of object
, removing the associated reference.
This function decreases the refcount of the object so the object
might not point to valid memory anymore after calling this function.
MT safe. Grabs and releases the object's lock.
object : |
GstObject to unparent |
gchar* gst_object_get_name_prefix (GstObject *object);
Returns a copy of the name prefix of the object.
Caller should g_free()
the return value after usage.
For a prefixless object, this returns NULL, which you can safely g_free()
as well.
void gst_object_set_name_prefix (GstObject *object, const gchar *name_prefix);
Sets the name prefix of the object. This function makes a copy of the provided name prefix, so the caller retains ownership of the name prefix it sent.
MT safe. This function grabs and releases the object's LOCK.
object : |
a GstObject to set the name prefix of |
name_prefix : |
new name prefix of object |
void gst_object_default_deep_notify (GObject *object, GstObject *orig, GParamSpec *pspec, gchar **excluded_props);
A default deep_notify signal callback for an element. The user data should contain a pointer to an array of strings that should be excluded from the notify. The default handler will print the new value of the property using g_print.
MT safe. This function grabs and releases the object's LOCK or getting the path string of the object.
object : |
the GObject that signalled the notify. |
orig : |
a GstObject that initiated the notify. |
pspec : |
a GParamSpec of the property. |
excluded_props : |
a set of user-specified properties to exclude or NULL to show all changes. |
void gst_object_default_error (GstObject *source, GError *error, gchar *debug);
A default error function.
The default handler will simply print the error string using g_print.
source : |
the GstObject that initiated the error. |
error : |
the GError. |
debug : |
an additional debug information string, or NULL. |
gboolean gst_object_check_uniqueness (GList *list, const gchar *name);
Checks to see if there is any object named name
in list
. This function
does not do any locking of any kind. You might want to protect the
provided list with the lock of the owner of the list. This function
will lock each GstObject in the list to compare the name, so be
carefull when passing a list with a locked object.
list : |
a list of GstObject to check through |
name : |
the name to search for |
Returns : | TRUE if the name does not appear in the list, FALSE if it does. MT safe. Grabs and releases the LOCK of each object in the list. |
gboolean gst_object_has_ancestor (GstObject *object, GstObject *ancestor);
Check if object
has an ancestor ancestor
somewhere up in
the hierarchy.
object : |
GstObject to check |
ancestor : |
GstObject to check as ancestor |
Returns : | TRUE if ancestor is an ancestor of object .
MT safe. Grabs and releases the object's locks.
|
xmlNodePtr gst_object_save_thyself (GstObject *object, xmlNodePtr parent);
Saves the given object into the parent XML node.
object : |
GstObject to save |
parent : |
The parent XML node to save the object into |
Returns : | the new xmlNodePtr with the saved object |
void gst_object_restore_thyself (GstObject *object, xmlNodePtr self);
Restores the given object with the data from the parent XML node.
object : |
GstObject to load into |
self : |
The XML node to load the object from |
gpointer gst_object_ref (gpointer object);
Increments the refence count on the object. This function does not take the lock on the object because it relies on atomic refcounting.
This object returns the input parameter to ease writing constructs like : result = gst_object_ref (object->parent);
object : |
GstObject to reference |
Returns : | A pointer to the object |
void gst_object_unref (gpointer object);
Decrements the refence count on the object. If reference count hits zero, destroy the object. This function does not take the lock on the object as it relies on atomic refcounting.
The unref method should never be called with the LOCK held since this might deadlock the dispose function.
object : |
GstObject to unreference |
void gst_object_sink (gpointer object);
Removes floating reference on an object. Any newly created object has a refcount of 1 and is FLOATING. This function should be used when creating a new object to symbolically 'take ownership' of the object. Use gst_object_set_parent to have this done for you.
MT safe. This function grabs and releases the object lock.
object : |
GstObject to sink |
void gst_object_replace (GstObject **oldobj, GstObject *newobj);
Unrefs the object pointer to by oldobj, refs the newobj and puts the newobj in *oldobj. Be carefull when calling this function, it does not take any locks. You might want to lock the object owning the oldobj pointer before calling this function.
Make sure not to LOCK the oldobj because it might be unreffed which could cause a deadlock when it is disposed.
oldobj : |
pointer to place of old GstObject |
newobj : |
new GstObject |
gchar* gst_object_get_path_string (GstObject *object);
Generates a string describing the path of the object in the object hierarchy. Only useful (or used) for debugging.
object : |
GstObject to get the path from |
Returns : | a string describing the path of the object. You must
g_free() the string after usage.
MT safe. Grabs and releases the object's LOCK for all objects
in the hierarchy.
|
guint gst_class_signal_connect (GstObjectClass *klass, const gchar *name, gpointer func, gpointer func_data);
Connect to a class signal.
klass : |
the GstObjectClass to attach the signal to |
name : |
the name of the signal to attach to |
func : |
the signal function |
func_data : |
a pointer to user data |
Returns : | the signal id. |
name
" property"name" gchararray : Read / Write / Construct
The name of the object.
Default value: NULL
void user_function (GstObject *gstobject, GObject *prop_object, GParamSpec *prop, gpointer user_data);
The deep notify signal is used to be notified of property changes. It is typically attached to the toplevel bin to receive notifications from all the elements contained in that bin.
gstobject : |
the object which received the signal. |
prop_object : |
the object that originated the signal |
prop : |
the property that changed |
user_data : |
user data set when the signal handler was connected. |
void user_function (GstObject *gstobject, gpointer xml_node, gpointer user_data);
Is trigered whenever a new object is saved to XML. You can connect to this signal to insert custom XML tags into the core XML.
gstobject : |
the object which received the signal. |
xml_node : |
the xmlNodePtr of the parent node |
user_data : |
user data set when the signal handler was connected. |
void user_function (GstObject *gstobject, GObject *parent, gpointer user_data);
Is emitted when the parent of an object is set.
gstobject : |
the object which received the signal. |
parent : |
the new parent |
user_data : |
user data set when the signal handler was connected. |
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