🚀 go-pugleaf

In article <justin.726213640@tasman>, justin@tasman.cc.utas.edu.au
(Justin Ridge) wrote:
> Is it possible to cancel a job which is being processed in a PS
> printer - specifically, in a Apple LaserWriter IINT/NTX/f/g?

For any PostScript printer data stream there is an "interrupt" command.
On serial and parallel streams, emit a ^C character. On Appletalk, I
do not know the command, but you could look it up in Inside Appletalk.
The effect of the command depends on the state of the printer job.

If the printer has already received and acknowledged the end-of-job,
the interrupt will not typically work, but will be interpreted as if
it was part of the next job. This means, for instance, that a job
which sets /#copies to 1000, does some simple drawing and a showpage,
then ends, cannot usually be interrupted once the end-of-job has been
processed. I say "usually" and "typically" because this behavior is not
well defined in the Red Book, and various clone implementations may
behave differently. (This is not meant as a slam against clones, just
an observation that they may choose to do things differently).

If the cancel was received before end-of-job, the behavior is much
more complex. Typically, it will be processed when the interpreter
next looks for input. This may occur ahead of characters received
earlier, due to buffer scanning. The interrupt will generate a
PostScript interrupt error, causing execution of the interrupt procedure
in errordict. This will typically cause an error message to be printed
and the rest of the job to be flushed.

If the printer has multiple pages in process or a sofware page pipeline,
some arbitrary number of pages may be printed after the interrupt.
Additionally, if the job has issued a read command against the input,
has set up an appropriate stopped contex, or has redefined the interrupt
procedure, it may be resistant to interrupts.

Stephen Zisk (zisk@adobe.com)  Disclaimer: These are my personal views
Adobe Systems Incorporated     and do not represent the position of
Eastern Regional Office        Adobe Systems Incorporated.
24 New England Exec. Park
Burlington, MA 01803           They pay me but they don't muzzle me!