Checks if task's #GCancellable has been cancelled, and if so, sets task's error accordingly and completes the task (see gio.task.Task.returnPointer for more discussion of exactly what this means).
true if task has been cancelled, false if not
Checks if task's #GCancellable has been cancelled, and if so, sets task's error accordingly and completes the task (see gio.task.Task.returnPointer for more discussion of exactly what this means).