Interface

Gio-2.0 ▶ Gio ▶ Cancellable ▶ SignalSignatures

interface SignalSignatures {
    cancelled: () => void;
    notify: (arg0: GObject.ParamSpec) => void;
}

Hierarchy (View Summary)

Index

Properties

cancelled

Properties - Inherited from GObject

notify

Properties

cancelled: () => void

Emitted when the operation has been cancelled.

Can be used by implementations of cancellable operations. If the operation is cancelled from another thread, the signal will be emitted in the thread that cancelled the operation, not the thread that is running the operation.

Note that disconnecting from this signal (or any signal) in a multi-threaded program is prone to race conditions. For instance it is possible that a signal handler may be invoked even after a call to g_signal_handler_disconnect() for that handler has already returned.

There is also a problem when cancellation happens right before connecting to the signal. If this happens the signal will unexpectedly not be emitted, and checking before connecting to the signal leaves a race condition where this is still happening.

In order to make it safe and easy to connect handlers there are two helper functions: g_cancellable_connect() and g_cancellable_disconnect() which protect against problems like this.

An example of how to us this:

    // Make sure we don't do unnecessary work if already cancelled
    if (g_cancellable_set_error_if_cancelled (cancellable, error))
      return;

    // Set up all the data needed to be able to handle cancellation
    // of the operation
    my_data = my_data_new (...);

    id = 0;
    if (cancellable)
      id = g_cancellable_connect (cancellable,
    			      G_CALLBACK (cancelled_handler)
    			      data, NULL);

    // cancellable operation here...

    g_cancellable_disconnect (cancellable, id);

    // cancelled_handler is never called after this, it is now safe
    // to free the data
    my_data_free (my_data);

Note that the cancelled signal is emitted in the thread that the user cancelled from, which may be the main thread. So, the cancellable signal should not do something that can block.

Properties - Inherited from GObject

notify: (arg0: GObject.ParamSpec) => void

The notify signal is emitted on an object when one of its properties has its value set through g_object_set_property(), g_object_set(), et al.

Note that getting this signal doesn’t itself guarantee that the value of the property has actually changed. When it is emitted is determined by the derived GObject class. If the implementor did not create the property with GObject.ParamFlags.EXPLICIT_NOTIFY, then any call to g_object_set_property() results in ::notify being emitted, even if the new value is the same as the old. If they did pass GObject.ParamFlags.EXPLICIT_NOTIFY, then this signal is emitted only when they explicitly call g_object_notify() or g_object_notify_by_pspec(), and common practice is to do that only when the value has actually changed.

This signal is typically used to obtain change notification for a single property, by specifying the property name as a detail in the g_signal_connect() call, like this:

g_signal_connect (text_view->buffer, "notify::paste-target-list",
                  G_CALLBACK (gtk_text_view_target_list_notify),
                  text_view)

It is important to note that you must use [canonical parameter names][class@GObject.ParamSpec#parameter-names] as detail strings for the notify signal.