Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!ucbvax!decwrl!hannah.dec.com!batcheldern
From: batcheldern@hannah.dec.com (Ned Batchelder, PostScript Eng.)
Newsgroups: comp.lang.postscript
Subject: Re: ^D embedded in PS files
Message-ID: <8905221304.AA14261@decwrl.dec.com>
Date: 22 May 89 13:04:25 GMT
Organization: Digital Equipment Corporation
Lines: 24

In article <645@cbnewsh.ATT.COM>, wcs@cbnewsh.ATT.COM (Bill Stewart) writes:
> But *why* should a spooler care about the end of a job?

In article <7279@pogo.WV.TEK.COM>, rick@pogo.WV.TEK.COM (Richard G.
Knowles), replies that accounting is a good reason.

Another good reason is that a queueing system should be able to tell when
an entry has safely left the queue.  For a printing system, that is only
when the job has successfully printed, and that can only be determined by
waiting for the ^D echo back from the printer.  

On VMS systems, you can PRINT/DELETE a file.  Users would be extremely
upset if the symbiont simply assumed that because it had sent all the data,
that the job had printed, and then deleted the file.  There are many ways
for a printer not to complete a job.

Another reason is for accurate notification of job completion.  Even if we
could assume that shipping the data to the printer guaranteed that the job
would complete, when would it complete?  By having an explicit handshake
between the spooler and the printer, the spooler knows that, in fact, the
job is completed, and if the user gets up from his desk and walks over to
the printer, he will be able to pick the job up and walk away.

Ned Batchelder, Digital Equipment Corp, BatchelderN@Hannah.DEC.com