Stops further processing of a print job.
If a service supports this method it cannot be concluded that
job cancellation will always suceeed. A job may not be able to be
cancelled once it has reached and passed some point in its processing.
A successful cancellation means only that the entire job was not
printed, some portion may already have printed when cancel returns.
The service will throw a PrintException if the cancellation did not
succeed. A job which has not yet been submitted for printing should
throw this exception.
Cancelling an already successfully cancelled Print Job is not
considered an error and will always succeed.
Cancellation in some services may be a lengthy process, involving
requests to a server and processing of its print queue. Clients
may wish to execute cancel in a thread which does not affect
application execution.