Re: How can I overwrite existing files with new input to running Ghostscript?.

Newsgroups	comp.lang.postscript
Date	2012-12-24 19:37 -0800
References	(5 earlier) <d4fef961-6eb2-4dac-8ffc-b89cc679297d@googlegroups.com> <a66bd6a2-8b88-4ffa-ae40-b2702b88b6e3@r13g2000vbd.googlegroups.com> <1e6eabe2-d9e0-49c0-926f-11beaab9ee0a@googlegroups.com> <fdfb2faa-a083-46eb-a222-e7154325419c@googlegroups.com> <cfd27480-0dc9-4175-b750-59a2b5ec15c6@b8g2000yqh.googlegroups.com>
Message-ID	<307b7d53-9ff3-4dfd-9eb2-fdce16e4bb85@googlegroups.com> (permalink)
Subject	Re: How can I overwrite existing files with new input to running Ghostscript?.
From	luser- -droog <mijoryx@yahoo.com>

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On Sunday, December 23, 2012 12:16:54 PM UTC-6, SaGS wrote:
> On Dec 23, 5:37 am, Ernie Kent <er...@erniekent.com> wrote:
> > ...
> > > This all works in the sense that the client can send multiple
> > > Postscript files to the server and GS will write each of
> > > them successively to the same jpeg file so that if GS is
> > > terminated at any point the last postscript input sent is
> > > then the image seen in the contents of the jpeg file.
> > > 
> > > However, no image is actually written to the file until GS
> > > is terminated.
> > ...
> > 1. If I manually start gs from the shell and enter the commands
> > of your script, there is no write to file until after I stop gs.
> > ...
> I agree with Chris, after the "restore" the outfile should be written
> and closed, unless there's a bug somewhere.
> I used Ubuntu with GS 8.61, and checked open files with "ls -l /proc/
> <pid>/fd". Once GS starts, only stdin/out/err are open. After
> "showpage" I see "out.jpg" opened too. After "restore" (without
        >
        > quitting GS or doing anything else) "out.jpg" isn't open anymore, and
> I can view the jpeg verifying its contents is what I expect it to be.
> I still suspect you have some trouble with syncing the various
> programs you run. 
> You have client(s) <-> daemon <-> gs. The/A client writes some info to
> trigger creating a new jpeg, but it takes time for the daemon to "see"
> that info and write to the pipe that connects it to GS. Then, the
> daemon flushes the write end of the pipe and continues checking for
> new requests from the client(s), but that does not mean GS had a
> chance to read all the code for the 1st request and execute it to
> completion. With your scheme, I don't see how the client can know if/
> when GS actually finished what it had to do (execute everything up to
        >
        > and including the "restore", and nothing more).
> If it will turn out the problems are with this syncing, then it is not
> something connected to PostScript or Ghostscript.


You could trying having ghostscript write an "I'm done!" message to a named pipe listened to by the "client".

(not tested)

    (gsmon.fifo)file dup(EOP\n)writestring closefile

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