Convenience function to connect to the "cancelled"
signal. Also handles the race condition that may happen
if the cancellable is cancelled right before connecting.
callback is called at most once, either directly at the
time of the connect if cancellable is already cancelled,
or when cancellable is cancelled in some thread.
data_destroy_func will be called when the handler is
disconnected, or immediately if the cancellable is already
cancelled.
See "cancelled" for details on how to use this.
Since 2.22
Convenience function to connect to the "cancelled" signal. Also handles the race condition that may happen if the cancellable is cancelled right before connecting. callback is called at most once, either directly at the time of the connect if cancellable is already cancelled, or when cancellable is cancelled in some thread. data_destroy_func will be called when the handler is disconnected, or immediately if the cancellable is already cancelled. See "cancelled" for details on how to use this. Since 2.22