Creates a source that triggers if @cancellable is cancelled and
calls its callback of type #GCancellableSourceFunc. This is
primarily useful for attaching to another (non-cancellable) source
with g_source_add_child_source() to add cancellability to it.
For convenience, you can call this with a %NULL #GCancellable,
in which case the source will never trigger.
The new #GSource will hold a reference to the #GCancellable.
Creates a source that triggers if @cancellable is cancelled and calls its callback of type #GCancellableSourceFunc. This is primarily useful for attaching to another (non-cancellable) source with g_source_add_child_source() to add cancellability to it.
For convenience, you can call this with a %NULL #GCancellable, in which case the source will never trigger.
The new #GSource will hold a reference to the #GCancellable.
Return: the new #GSource.