## GstObject

GstObject — Base class for the GStreamer object hierarchy

## Synopsis

    #include <gst/gst.h>

                        GstObject;
                        GstObjectClass;
    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_ref_sink                 (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
             +----GstPadTemplate
             +----GstPluginFeature
             +----GstElement
             +----GstBus
             +----GstTask
             +----GstTaskPool
             +----GstClock
             +----GstPlugin
             +----GstRegistry
             +----GstIndex
             +----GstXML

## Known Derived Interfaces

GstObject is required by GstChildProxy.

## Properties

      "name"                     gchar*                : 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:

    1
    2

    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:

    1
    2
    3
    4

    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;    /* unused (FIXME 0.11: remove) */

      GMutex        *lock;        /* object LOCK */
      gchar         *name;        /* object name */
      gchar         *name_prefix; /* (un)used for debugging (FIXME 0.11: remove) */
      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`; | unused
GstObject *`parent`; | this object's parent, weak ref
guint32 `flags`; | use GST_OBJECT_IS_XXX macros to access the flags

### GstObjectClass

    typedef struct {
      GObjectClass parent_class;

      const gchar *path_string_separator;
      GObject *signal_object;

      /* FIXME-0.11: remove this, plus the above GST_CLASS_*_LOCK macros */
      GStaticRecMutex *lock;

      /* signals */
      /* FIXME-0.11: remove, and pass NULL in g_signal_new(), we never used them */
      void          (*parent_set)       (GstObject * object, GstObject * parent);
      void          (*parent_unset)     (GstObject * object, GstObject * parent);
      /* FIXME 0.11: Remove this, it's deprecated */
      void          (*object_saved)     (GstObject * object, GstXmlNodePtr parent);
      void          (*deep_notify)      (GstObject * object, GstObject * orig, GParamSpec * pspec);

      /* virtual methods for subclasses */
      /* FIXME 0.11: Remove this, it's deprecated */
      GstXmlNodePtr (*save_thyself)     (GstObject * object, GstXmlNodePtr parent);
      void          (*restore_thyself)  (GstObject * object, GstXmlNodePtr self);
    } GstObjectClass;

GStreamer base object class.

GObjectClass `parent_class`; | parent
const gchar *`path_string_separator`; | separator used by `gst_object_get_path_string()`
GObject *`signal_object`; | is used to signal to the whole class
GStaticRecMutex *`lock`; | class lock to be used with `GST_CLASS_GET_LOCK()`, `GST_CLASS_LOCK()`, `GST_CLASS_UNLOCK()` and others.
`parent_set` () | default signal handler
`parent_unset` () | default signal handler
`object_saved` () | default signal handler
`deep_notify` () | default signal handler
`save_thyself` () | xml serialisation
`restore_thyself` () | xml de-serialisation

### 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, don't 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 GstObject.

### 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);

### Warning

`gst_object_get_name_prefix` is deprecated and should not be used in newly-written code. deprecated because the name prefix has never actually been used for anything.

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);

### Warning

`gst_object_set_name_prefix` is deprecated and should not be used in newly-written code. deprecated because the name prefix has never actually been used for anything.

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. One can e.g. check if a GstElement is inside a GstPipeline.

`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);

### Warning

`gst_object_save_thyself` is deprecated and should not be used in newly-written code.

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);

### Warning

`gst_object_restore_thyself` is deprecated and should not be used in newly-written code.

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 reference 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 reference 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_ref_sink ()

    void                gst_object_ref_sink                 (gpointer object);

Increase the reference count of `object`, and possibly remove the floating reference, if `object` has a floating reference.

In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

MT safe. This function grabs and releases `object` lock.

`object` : | a GstObject to sink

Since 0.10.24

### 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);

### Warning

`gst_class_signal_emit_by_name` is deprecated and should not be used in newly-written code.

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"                     gchar*                : 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,
                                                            GstObject *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,
                                                            GstObject *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.