GIO Reference Manual: Watching Bus Names

## Watching Bus Names Watching Bus Names — Simple API for watching bus names |

## Functions

void | (*GBusNameAppearedCallback) ()
void | (*GBusNameVanishedCallback) ()
guint | g_bus_watch_name ()
guint | g_bus_watch_name_on_connection ()
void | g_bus_unwatch_name ()
guint | g_bus_watch_name_with_closures ()
guint | g_bus_watch_name_on_connection_with_closures ()

## Types and Values

enum | GBusNameWatcherFlags

## Includes

    #include <gio/gio.h>

## Description

Convenience API for watching bus names.

A simple example for watching a name can be found in gdbus-example-watch-name.c

## Functions

### GBusNameAppearedCallback ()

    void
    (*GBusNameAppearedCallback) (GDBusConnection *connection,
                                 const gchar *name,
                                 const gchar *name_owner,
                                 gpointer user_data);

Invoked when the name being watched is known to have to have a owner.

#### Parameters

connection | The GDBusConnection the name is being watched on. |
name | The name being watched. |
name_owner | Unique name of the owner of the name being watched. |
user_data | User data passed to `g_bus_watch_name()`. |

Since 2.26

### GBusNameVanishedCallback ()

    void
    (*GBusNameVanishedCallback) (GDBusConnection *connection,
                                 const gchar *name,
                                 gpointer user_data);

Invoked when the name being watched is known not to have to have a owner.

This is also invoked when the GDBusConection on which the watch was established has been closed. In that case, `connection` will be `NULL`.

#### Parameters

connection | The GDBusConnection the name is being watched on, or `NULL`. |
name | The name being watched. |
user_data | User data passed to `g_bus_watch_name()`. |

Since 2.26

### g_bus_watch_name ()

    guint
    g_bus_watch_name (GBusType bus_type,
                      const gchar *name,
                      GBusNameWatcherFlags flags,
                      GBusNameAppearedCallback name_appeared_handler,
                      GBusNameVanishedCallback name_vanished_handler,
                      gpointer user_data,
                      GDestroyNotify user_data_free_func);

Starts watching `name` on the bus specified by `bus_type` and calls `name_appeared_handler` and `name_vanished_handler` when the name is known to have a owner respectively known to lose its owner. Callbacks will be invoked in the thread-default main context of the thread you are calling this function from.

You are guaranteed that one of the handlers will be invoked after calling this function. When you are done watching the name, just call `g_bus_unwatch_name()` with the watcher id this function returns.

If the name vanishes or appears (for example the application owning the name could restart), the handlers are also invoked. If the GDBusConnection that is used for watching the name disconnects, then `name_vanished_handler` is invoked since it is no longer possible to access the name.

Another guarantee is that invocations of `name_appeared_handler` and `name_vanished_handler` are guaranteed to alternate; that is, if `name_appeared_handler` is invoked then you are guaranteed that the next time one of the handlers is invoked, it will be `name_vanished_handler` . The reverse is also true.

This behavior makes it very simple to write applications that want to take action when a certain name exists. Basically, the application should create object proxies in `name_appeared_handler` and destroy them again (if any) in `name_vanished_handler` .

#### Parameters

bus_type | The type of bus to watch a name on. |
name | The name (well-known or unique) to watch. |
flags | Flags from the GBusNameWatcherFlags enumeration. |
name_appeared_handler | Handler to invoke when `name` is known to exist or `NULL`. | [allow-none]
name_vanished_handler | Handler to invoke when `name` is known to not exist or `NULL`. | [allow-none]
user_data | User data to pass to handlers. |
user_data_free_func | Function for freeing `user_data` or `NULL`. | [allow-none]

#### Returns

An identifier (never 0) that an be used with `g_bus_unwatch_name()` to stop watching the name.

Since 2.26

### g_bus_watch_name_on_connection ()

    guint
    g_bus_watch_name_on_connection (GDBusConnection *connection,
                                    const gchar *name,
                                    GBusNameWatcherFlags flags,
                                    GBusNameAppearedCallback name_appeared_handler,
                                    GBusNameVanishedCallback name_vanished_handler,
                                    gpointer user_data,
                                    GDestroyNotify user_data_free_func);

Like `g_bus_watch_name()` but takes a GDBusConnection instead of a GBusType.

#### Parameters

connection | A GDBusConnection. |
name | The name (well-known or unique) to watch. |
flags | Flags from the GBusNameWatcherFlags enumeration. |
name_appeared_handler | Handler to invoke when `name` is known to exist or `NULL`. | [allow-none]
name_vanished_handler | Handler to invoke when `name` is known to not exist or `NULL`. | [allow-none]
user_data | User data to pass to handlers. |
user_data_free_func | Function for freeing `user_data` or `NULL`. | [allow-none]

#### Returns

An identifier (never 0) that an be used with `g_bus_unwatch_name()` to stop watching the name.

Since 2.26

### g_bus_unwatch_name ()

    void
    g_bus_unwatch_name (guint watcher_id);

Stops watching a name.

#### Parameters

watcher_id | An identifier obtained from `g_bus_watch_name()` |

Since 2.26

### g_bus_watch_name_with_closures ()

    guint
    g_bus_watch_name_with_closures (GBusType bus_type,
                                    const gchar *name,
                                    GBusNameWatcherFlags flags,
                                    GClosure *name_appeared_closure,
                                    GClosure *name_vanished_closure);

Version of `g_bus_watch_name()` using closures instead of callbacks for easier binding in other languages.

#### Parameters

bus_type | The type of bus to watch a name on. |
name | The name (well-known or unique) to watch. |
flags | Flags from the GBusNameWatcherFlags enumeration. |
name_appeared_closure | GClosure to invoke when `name` is known to exist or `NULL`. | [allow-none]
name_vanished_closure | GClosure to invoke when `name` is known to not exist or `NULL`. | [allow-none]

#### Returns

An identifier (never 0) that an be used with `g_bus_unwatch_name()` to stop watching the name.

Rename to: g_bus_watch_name

Since 2.26

### g_bus_watch_name_on_connection_with_closures ()

    guint
    g_bus_watch_name_on_connection_with_closures
                                   (GDBusConnection *connection,
                                    const gchar *name,
                                    GBusNameWatcherFlags flags,
                                    GClosure *name_appeared_closure,
                                    GClosure *name_vanished_closure);

Version of `g_bus_watch_name_on_connection()` using closures instead of callbacks for easier binding in other languages.

#### Parameters

connection | A GDBusConnection. |
name | The name (well-known or unique) to watch. |
flags | Flags from the GBusNameWatcherFlags enumeration. |
name_appeared_closure | GClosure to invoke when `name` is known to exist or `NULL`. | [allow-none]
name_vanished_closure | GClosure to invoke when `name` is known to not exist or `NULL`. | [allow-none]

#### Returns

An identifier (never 0) that an be used with `g_bus_unwatch_name()` to stop watching the name.

Rename to: g_bus_watch_name_on_connection

Since 2.26

## Types and Values

### enum GBusNameWatcherFlags

Flags used in `g_bus_watch_name()`.

#### Members

G_BUS_NAME_WATCHER_FLAGS_NONE | No flags set. |
G_BUS_NAME_WATCHER_FLAGS_AUTO_START | If no-one owns the name when beginning to watch the name, ask the bus to launch an owner for the name. |

Since 2.26