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From: les@chinet.chi.il.us (Leslie Mikesell)
Newsgroups: comp.lang.postscript
Subject: Re: SUMMARY:  Is HP PostScript known to hang mysteriously?
Message-ID: <1991Jan21.154315.26905@chinet.chi.il.us>
Date: 21 Jan 91 15:43:15 GMT
References: <1060@quiddity.queensu.CA>
Organization: Chinet - Public Access UNIX
Lines: 27

In article <1060@quiddity.queensu.CA> jorgnsn@qucis.queensu.ca (John Jorgensen) writes:
>On December 4, I asked what to do about two HP LaserJet IIIs with HP's
>PostScript cartridge, which were hanging intermittently on perfectly
>good PostScript jobs.  The printers showed "PROCESSING DATA"
>indefinitely, without any pages coming out.  Occasionally I could take
>the printers offline and reset them from the front panel, but usually
>I couldn't get past "OFFLINE PENDING", and had to switch the printer
>off to reset it.  Most, but not all, of the hanging jobs were produced
>by a DVI-to-PostScript translator called dvitps.  The same jobs would
>print fine when resubmitted.

I don't think your summary covered the simple and likely posibility
that the printer is returning data to the host and becomes deadlocked
due to the host sending and XOFF to the printer.  This will happen
in the case where you have enabled XON/XOFF flow control from the
host to the printer and do not read from the port often enough to
collect the data returned.  The printer will not continue until it
has been able to output any data that may have been requested by
commands embedded in the postscript file.  To test for this, when the
printer is apparently hung, just do a "cat </dev/ttyxx" using the
appropriate port name.  If that clears the condition, then the problem was
the reverse flow control.  To fix it, either eliminate the XON/XOFF from
the host and allow the data to be discarded or fork a process to
read continuously to avoid deadlock.

Les Mikesell
  les@chinet.chi.il.us