GstObject

GstObject — Base class for the GStreamer object hierarchy

Synopsis


#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_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)
#define             GST_OBJECT_LOCK                     (obj)
#define             GST_OBJECT_TRYLOCK                  (obj)
#define             GST_OBJECT_UNLOCK                   (obj)
#define             GST_OBJECT_GET_LOCK                 (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);
GstXmlNodePtr       gst_object_save_thyself             (GstObject *object,
                                                         GstXmlNodePtr parent);
void                gst_object_restore_thyself          (GstObject *object,
                                                         GstXmlNodePtr 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,
                                                         GstXmlNodePtr self);


Object Hierarchy


  GObject
   +----GstObject
         +----GstPad
         +----GstPluginFeature
         +----GstElement
         +----GstPlugin
         +----GstRegistry
         +----GstBus
         +----GstClock
         +----GstIndex
         +----GstPadTemplate
         +----GstTask
         +----GstXML

Known Derived Interfaces

GstObject is required by GstChildProxy.

Properties


  "name"                     gchararray            : Read / Write / Construct

Signals


  "deep-notify"                                    : Run First / No Recursion / Has Details / No Hooks
  "object-saved"                                   : Run Last
  "parent-set"                                     : Run Last
  "parent-unset"                                   : Run Last

Description

GstObject provides a root for the object hierarchy tree filed in by the GStreamer 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; 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, which then manages the lifetime of the object itself:

   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().

Special care has to be taken for all methods that gst_object_sink() an object since if the caller of those functions had a floating reference to the object, the object reference is now invalid.

In contrast to GObject instances, GstObject adds a name property. The functions gst_object_set_name() and gst_object_get_name() are used to set/get the name of the object.

Last reviewed on 2005-11-09 (0.9.4)

Details

GstObject

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.

gint refcount; unused
GMutex *lock; object LOCK
gchar *name; The name of the object
gchar *name_prefix; used for debugging
GstObject *parent; this object's parent, weak ref
guint32 flags; use GST_OBJECT_IS_XXX macros to access the flags

enum GstObjectFlags

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

GST_OBJECT_FLAGS()

#define GST_OBJECT_FLAGS(obj)                  (GST_OBJECT_CAST (obj)->flags)

This macro returns the entire set of flags for the object.

obj : a GstObject

GST_OBJECT_FLAG_IS_SET()

#define GST_OBJECT_FLAG_IS_SET(obj,flag)       ((GST_OBJECT_FLAGS (obj) & (flag)) == (flag))

This macro checks to see if the given flag is set.

obj : a GstObject
flag : Flag to check for

GST_OBJECT_FLAG_SET()

#define GST_OBJECT_FLAG_SET(obj,flag)          (GST_OBJECT_FLAGS (obj) |= (flag))

This macro sets the given bits.

obj : a GstObject
flag : Flag to set

GST_OBJECT_FLAG_UNSET()

#define GST_OBJECT_FLAG_UNSET(obj,flag)        (GST_OBJECT_FLAGS (obj) &= ~(flag))

This macro usets the given bits.

obj : a GstObject
flag : Flag to set

GST_OBJECT_NAME()

#define GST_OBJECT_NAME(obj)            (GST_OBJECT_CAST(obj)->name)

Get the name of this object

obj : a GstObject

GST_OBJECT_PARENT()

#define GST_OBJECT_PARENT(obj)          (GST_OBJECT_CAST(obj)->parent)

Get the parent of this object

obj : a GstObject

GST_OBJECT_IS_DISPOSING()

#define GST_OBJECT_IS_DISPOSING(obj)    (GST_OBJECT_FLAG_IS_SET (obj, GST_OBJECT_DISPOSING))

Check if the given object is beeing destroyed.

obj : a GstObject

GST_OBJECT_IS_FLOATING()

#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 : a GstObject

GST_OBJECT_REFCOUNT()

#define GST_OBJECT_REFCOUNT(obj)                (((GObject*)(obj))->ref_count)

Get access to the reference count field of the object.

obj : a GstObject

GST_OBJECT_REFCOUNT_VALUE()

#define GST_OBJECT_REFCOUNT_VALUE(obj)          g_atomic_int_get ((gint *) &GST_OBJECT_REFCOUNT(obj))

Get the reference count value of the object.

obj : a GstObject

GST_CLASS_GET_LOCK()

#define GST_CLASS_GET_LOCK(obj)         (GST_OBJECT_CLASS_CAST(obj)->lock)

This macro will return the class lock used to protect deep_notify signal emission on thread-unsafe glib versions (glib < 2.8).

obj : a GstObjectClass

GST_CLASS_LOCK()

#define GST_CLASS_LOCK(obj)             (g_static_rec_mutex_lock(GST_CLASS_GET_LOCK(obj)))

Lock the class.

obj : a GstObjectClass

GST_CLASS_TRYLOCK()

#define GST_CLASS_TRYLOCK(obj)          (g_static_rec_mutex_trylock(GST_CLASS_GET_LOCK(obj)))

Try to lock the class, returns TRUE if class could be locked.

obj : a GstObjectClass

GST_CLASS_UNLOCK()

#define GST_CLASS_UNLOCK(obj)           (g_static_rec_mutex_unlock(GST_CLASS_GET_LOCK(obj)))

Unlock the class.

obj : a GstObjectClass

GST_OBJECT_LOCK()

#define GST_OBJECT_LOCK(obj)                   g_mutex_lock(GST_OBJECT_GET_LOCK(obj))

This macro will obtain a lock on the object, making serialization possible. It blocks until the lock can be obtained.

obj : a GstObject to lock

GST_OBJECT_TRYLOCK()

#define GST_OBJECT_TRYLOCK(obj)                g_mutex_trylock(GST_OBJECT_GET_LOCK(obj))

This macro will try to obtain a lock on the object, but will return with FALSE if it can't get it immediately.

obj : a Object.

GST_OBJECT_UNLOCK()

#define GST_OBJECT_UNLOCK(obj)                 g_mutex_unlock(GST_OBJECT_GET_LOCK(obj))

This macro releases a lock on the object.

obj : a GstObject to unlock.

GST_OBJECT_GET_LOCK()

#define GST_OBJECT_GET_LOCK(obj)               (GST_OBJECT_CAST(obj)->lock)

Acquire a reference to the mutex of this object.

obj : a GstObject

gst_object_set_name ()

gboolean            gst_object_set_name                 (GstObject *object,
                                                         const gchar *name);

Sets the name of object, or gives 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
name : new name of object
Returns : TRUE if the name could be set. Since Objects that have a parent cannot be renamed, this function returns FALSE in those cases. MT safe. This function grabs and releases object's LOCK.

gst_object_get_name ()

gchar*              gst_object_get_name                 (GstObject *object);

Returns a copy of the name of 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.

object : a GstObject
Returns : the name of object. g_free() after usage. MT safe. This function grabs and releases object's LOCK.

gst_object_set_parent ()

gboolean            gst_object_set_parent               (GstObject *object,
                                                         GstObject *parent);

Sets the parent of object to parent. The object's reference count will be incremented, and any floating reference will be removed (see gst_object_sink()).

This function causes the parent-set signal to be emitted when the parent was successfully set.

object : a GstObject
parent : new parent of object
Returns : TRUE if parent could be set or FALSE when object already had a parent or object and parent are the same. MT safe. Grabs and releases object's LOCK.

gst_object_get_parent ()

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 : a GstObject
Returns : parent of object, this can be NULL if object has no parent. unref after usage. MT safe. Grabs and releases object's LOCK.

gst_object_unparent ()

void                gst_object_unparent                 (GstObject *object);

Clear the parent of object, removing the associated reference. This function decreases the refcount of object.

MT safe. Grabs and releases object's lock.

object : a GstObject to unparent

gst_object_get_name_prefix ()

gchar*              gst_object_get_name_prefix          (GstObject *object);

Returns a copy of the name prefix of 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.

object : a GstObject
Returns : the name prefix of object. g_free() after usage. MT safe. This function grabs and releases object's LOCK.

gst_object_set_name_prefix ()

void                gst_object_set_name_prefix          (GstObject *object,
                                                         const gchar *name_prefix);

Sets the name prefix of object to name_prefix. 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 object's LOCK.

object : a GstObject
name_prefix : new name prefix of object

gst_object_default_deep_notify ()

void                gst_object_default_deep_notify      (GObject *object,
                                                         GstObject *orig,
                                                         GParamSpec *pspec,
                                                         gchar **excluded_props);

A default deep_notify signal callback for an object. 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 object's LOCK for getting its path string.

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.

gst_object_default_error ()

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.

gst_object_check_uniqueness ()

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 a GstObject named name does not appear in list, FALSE if it does. MT safe. Grabs and releases the LOCK of each object in the list.

gst_object_has_ancestor ()

gboolean            gst_object_has_ancestor             (GstObject *object,
                                                         GstObject *ancestor);

Check if object has an ancestor ancestor somewhere up in the hierarchy.

object : a GstObject to check
ancestor : a GstObject to check as ancestor
Returns : TRUE if ancestor is an ancestor of object. MT safe. Grabs and releases object's locks.

gst_object_save_thyself ()

GstXmlNodePtr       gst_object_save_thyself             (GstObject *object,
                                                         GstXmlNodePtr parent);

Saves object into the parent XML node.

object : a GstObject to save
parent : The parent XML node to save object into
Returns : the new xmlNodePtr with the saved object

gst_object_restore_thyself ()

void                gst_object_restore_thyself          (GstObject *object,
                                                         GstXmlNodePtr self);

Restores object with the data from the parent XML node.

object : a GstObject to load into
self : The XML node to load object from

gst_object_ref ()

gpointer            gst_object_ref                      (gpointer object);

Increments the refence count on object. This function does not take the lock on 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 : a GstObject to reference
Returns : A pointer to object

gst_object_unref ()

void                gst_object_unref                    (gpointer object);

Decrements the refence count on object. If reference count hits zero, destroy object. This function does not take the lock on 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 : a GstObject to unreference

gst_object_sink ()

void                gst_object_sink                     (gpointer object);

If object was floating, the GST_OBJECT_FLOATING flag is removed and object is unreffed. When object was not floating, this function does nothing.

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 object. This done by first doing a gst_object_ref() to keep a reference to object and then gst_object_sink() to remove and unref any floating references to object. Use gst_object_set_parent() to have this done for you.

MT safe. This function grabs and releases object lock.

object : a GstObject to sink

gst_object_replace ()

void                gst_object_replace                  (GstObject **oldobj,
                                                         GstObject *newobj);

Unrefs the GstObject pointed to by oldobj, refs newobj and puts newobj in *oldobj. Be carefull when calling this function, it does not take any locks. You might want to lock the object owning oldobj pointer before calling this function.

Make sure not to LOCK oldobj because it might be unreffed which could cause a deadlock when it is disposed.

oldobj : pointer to a place of a GstObject to replace
newobj : a new GstObject

gst_object_get_path_string ()

gchar*              gst_object_get_path_string          (GstObject *object);

Generates a string describing the path of object in the object hierarchy. Only useful (or used) for debugging.

object : a GstObject
Returns : a string describing the path of object. You must g_free() the string after usage. MT safe. Grabs and releases the GstObject's LOCK for all objects in the hierarchy.

gst_class_signal_connect ()

guint               gst_class_signal_connect            (GstObjectClass *klass,
                                                         const gchar *name,
                                                         gpointer func,
                                                         gpointer func_data);

Connect to a class signal.

klass : a 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.

gst_class_signal_emit_by_name ()

void                gst_class_signal_emit_by_name       (GstObject *object,
                                                         const gchar *name,
                                                         GstXmlNodePtr self);

emits the named class signal.

object : a GstObject that emits the signal
name : the name of the signal to emit
self : data for the signal

Property Details

The "name" property

  "name"                     gchararray            : Read / Write / Construct

The name of the object.

Default value: NULL

Signal Details

The "deep-notify" signal

void                user_function                      (GstObject  *gstobject,
                                                        GstObject  *prop_object,
                                                        GParamSpec *prop,
                                                        gpointer    user_data)        : Run First / No Recursion / Has Details / No Hooks

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 : a GstObject
prop_object : the object that originated the signal
prop : the property that changed
user_data : user data set when the signal handler was connected.

The "object-saved" signal

void                user_function                      (GstObject *gstobject,
                                                        gpointer   xml_node,
                                                        gpointer   user_data)      : Run Last

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 : a GstObject
xml_node : the xmlNodePtr of the parent node
user_data : user data set when the signal handler was connected.

The "parent-set" signal

void                user_function                      (GstObject *gstobject,
                                                        GObject   *parent,
                                                        gpointer   user_data)      : Run Last

Emitted when the parent of an object is set.

gstobject : a GstObject
parent : the new parent
user_data : user data set when the signal handler was connected.

The "parent-unset" signal

void                user_function                      (GstObject *gstobject,
                                                        GObject   *parent,
                                                        gpointer   user_data)      : Run Last

Emitted when the parent of an object is unset.

gstobject : a GstObject
parent : the old parent
user_data : user data set when the signal handler was connected.