| | | GStreamer 0.8 Core Reference Manual | |
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GstObject — Base class for the GStreamer object hierarchy
#include <gst/gst.h> struct GstObject; enum GstObjectFlags; #define GST_FLAGS (obj) #define GST_FLAG_IS_SET (obj,flag) #define GST_FLAG_SET (obj,flag) #define GST_FLAG_UNSET (obj,flag) #define GST_OBJECT_NAME (obj) #define GST_OBJECT_PARENT (obj) #define GST_OBJECT_DESTROYED (obj) #define GST_OBJECT_FLOATING (obj) #define GST_LOCK (obj) #define GST_TRYLOCK (obj) #define GST_UNLOCK (obj) #define GST_GET_LOCK (obj) void gst_object_set_name (GstObject *object, const gchar *name); G_CONST_RETURN gchar* gst_object_get_name (GstObject *object); void gst_object_set_parent (GstObject *object, GstObject *parent); GstObject* gst_object_get_parent (GstObject *object); void gst_object_unparent (GstObject *object); void gst_object_default_deep_notify (GObject *object, GstObject *orig, GParamSpec *pspec, gchar **excluded_props); gboolean gst_object_check_uniqueness (GList *list, const gchar *name); xmlNodePtr gst_object_save_thyself (GstObject *object, xmlNodePtr parent); void gst_object_restore_thyself (GstObject *object, xmlNodePtr self); GstObject* gst_object_ref (GstObject *object); void gst_object_unref (GstObject *object); void gst_object_sink (GstObject *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
+----GstElement
+----GstPadTemplate
+----GstClock
+----GstIndex
+----GstScheduler
+----GstXML
"deep-notify" void user_function (GstObject *gstobject, GObject *arg1, GParamSpec *arg2, gpointer user_data); "object-saved" void user_function (GstObject *gstobject, gpointer arg1, gpointer user_data); "parent-set" void user_function (GstObject *gstobject, GObject *arg1, gpointer user_data); "parent-unset" void user_function (GstObject *gstobject, GObject *arg1, 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 */ gtk_bin_add (GTK_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().
gst_object_set_name() and gst_object_get_name() are used to set/get the name of the object.
typedef enum
{
GST_DESTROYED = 0,
GST_FLOATING,
GST_OBJECT_FLAG_LAST = 4
} GstObjectFlags;
Flags for an object
| GST_DESTROYED | The object is flagged for destruction |
| GST_FLOATING | The object is created but has no parent yet to manage it |
| GST_OBJECT_FLAG_LAST | subclasses can add additional flags starting from this flag |
#define GST_FLAGS(obj) (GST_OBJECT (obj)->flags)
This macro returns the entire set of flags for the object.
| obj : | Object to return flags for. |
#define GST_FLAG_IS_SET(obj,flag) (GST_FLAGS (obj) & (1<<(flag)))
This macro checks to see if the given flag is set.
| obj : | GstSrc to check for flag in. |
| flag : | Flag to check for, must be a single bit in guint32. |
#define GST_FLAG_SET(obj,flag) G_STMT_START{ (GST_FLAGS (obj) |= (1<<(flag))); }G_STMT_END
This macro sets the given bits.
| obj : | Object to set flag in. |
| flag : | Flag to set, can by any number of bits in guint32. |
#define GST_FLAG_UNSET(obj,flag) G_STMT_START{ (GST_FLAGS (obj) &= ~(1<<(flag))); }G_STMT_END
This macro usets the given bits.
| obj : | Object to unset flag in. |
| flag : | Flag to set, must be a single bit in guint32. |
#define GST_OBJECT_NAME(obj) (const gchar*)(((GstObject *)(obj))->name)
Get the name of this object
| obj : | Object to get the name of. |
#define GST_OBJECT_PARENT(obj) (((GstObject *)(obj))->parent)
Get the parent of this object
| obj : | Object to get the parent of. |
#define GST_OBJECT_DESTROYED(obj) (GST_FLAG_IS_SET (obj, GST_DESTROYED))
Check if the object has been destroyed.
| obj : | The Object to check |
#define GST_OBJECT_FLOATING(obj) (GST_FLAG_IS_SET (obj, GST_FLOATING))
Check if the object is floating.
| obj : | The Object to check |
#define GST_LOCK(obj) (g_mutex_lock(GST_OBJECT(obj)->lock))
This macro will obtain a lock on the object, making serialization possible.
| obj : | Object to lock. |
#define GST_TRYLOCK(obj) (g_mutex_trylock(GST_OBJECT(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_UNLOCK(obj) (g_mutex_unlock(GST_OBJECT(obj)->lock))
This macro releases a lock on the object.
| obj : | Object to unlock. |
#define GST_GET_LOCK(obj) (GST_OBJECT(obj)->lock)
Acquire a reference to the mutex of this object.
| obj : | Object to get the mutex of. |
void gst_object_set_name (GstObject *object, const gchar *name);
Sets the name of the object, or gives the element a guaranteed unique name (if name is NULL).
| object : | GstObject to set the name of |
| name : | new name of object |
G_CONST_RETURN gchar* gst_object_get_name (GstObject *object);
Get the name of the object.
| object : | GstObject to get the name of |
| Returns : | name of the object |
void 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 |
GstObject* gst_object_get_parent (GstObject *object);
Returns the parent of object.
| object : | GstObject to get parent of |
| Returns : | parent of the object |
void gst_object_unparent (GstObject *object);
Clear the parent of object, removing the associated reference.
| object : | GstObject to unparent |
void gst_object_default_deep_notify (GObject *object,
GstObject *orig,
GParamSpec *pspec,
gchar **excluded_props);Adds a default deep_notify signal callback to 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.
| 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. |
gboolean gst_object_check_uniqueness (GList *list,
const gchar *name);Checks to see if there is any object named name in list.
| 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. |
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 |
GstObject* gst_object_ref (GstObject *object);
Increments the refence count on the object.
| object : | GstObject to reference |
| Returns : | A pointer to the object |
void gst_object_unref (GstObject *object);
Decrements the refence count on the object. If reference count hits zero, destroy the object.
| object : | GstObject to unreference |
void gst_object_sink (GstObject *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.
| 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.
| 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 |
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. |
void gst_class_signal_emit_by_name (GstObject *object, const gchar *name, xmlNodePtr self);
emits the named class signal.
| object : | the object that sends the signal |
| name : | the name of the signal to emit |
| self : | data for the signal |
void user_function (GstObject *gstobject, GObject *arg1, GParamSpec *arg2, 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. |
| arg1 : | the object that originated the signal |
| arg2 : | the property that changed |
| user_data : | user data set when the signal handler was connected. |
void user_function (GstObject *gstobject, gpointer arg1, 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. |
| arg1 : | the xmlNodePtr of the parent node |
| user_data : | user data set when the signal handler was connected. |
void user_function (GstObject *gstobject, GObject *arg1, gpointer user_data);
Is emitted when the parent of an object is set.
| gstobject : | the object which received the signal. |
| arg1 : | the new parent |
| user_data : | user data set when the signal handler was connected. |
void user_function (GstObject *gstobject, GObject *arg1, gpointer user_data);
Is emitted when the parent of an object is unset.
| gstobject : | the object which received the signal. |
| arg1 : | the old parent |
| user_data : | user data set when the signal handler was connected. |
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