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gdbusconnection: Document threading and refcounting for signals

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This is essentially a mini writeup of #978.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #978
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Philip Withnall 2020-01-20 11:37:48 +00:00
parent a434bfbb3d
commit 37b1acdf8c
1 changed files with 18 additions and 0 deletions
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18
gio/gdbusconnection.c
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@ -3468,6 +3468,24 @@ is_signal_data_for_name_lost_or_acquired (SignalData *signal_data)
* signal is unsubscribed from, and may be called after @connection * signal is unsubscribed from, and may be called after @connection
* has been destroyed.) * has been destroyed.)
* *
* As @callback is potentially invoked in a different thread from where it’s
* emitted, it’s possible for this to happen after
* g_dbus_connection_signal_unsubscribe() has been called in another thread.
* Due to this, @user_data should have a strong reference which is freed with
* @user_data_free_func, rather than pointing to data whose lifecycle is tied
* to the signal subscription. For example, if a #GObject is used to store the
* subscription ID from g_dbus_connection_signal_subscribe(), a strong reference
* to that #GObject must be passed to @user_data, and g_object_unref() passed to
* @user_data_free_func. You are responsible for breaking the resulting
* reference count cycle by explicitly unsubscribing from the signal when
* dropping the last external reference to the #GObject. Alternatively, a weak
* reference may be used.
*
* It is guaranteed that if you unsubscribe from a signal using
* g_dbus_connection_signal_unsubscribe() from the same thread which made the
* corresponding g_dbus_connection_signal_subscribe() call, @callback will not
* be invoked after g_dbus_connection_signal_unsubscribe() returns.
*
* The returned subscription identifier is an opaque value which is guaranteed * The returned subscription identifier is an opaque value which is guaranteed
* to never be zero. * to never be zero.
* *