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Make ghostscript signal an /interrupt error when it received a SIGINT

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  Make ghostscript signal an /interrupt error when it received a SIGINT luser- -droog <mijoryx@yahoo.com> - 2013-04-25 16:32 -0700
    Re: Make ghostscript signal an /interrupt error when it received a SIGINT luser- -droog <mijoryx@yahoo.com> - 2013-04-26 15:33 -0700
    Re: Make ghostscript signal an /interrupt error when it received a SIGINT Helge Blischke <h.blischke@acm.org> - 2013-04-30 18:35 +0200
      Re: Make ghostscript signal an /interrupt error when it received a SIGINT luser- -droog <mijoryx@yahoo.com> - 2013-04-30 20:26 -0700

#1372 — Make ghostscript signal an /interrupt error when it received a SIGINT

With my Mandelbrot explorer (https://code.google.com/p/xpost/downloads/detail?name=mandel2.ps),
I'd like to be able to interrupt the drawing and return to the menu if 
the resolution is too high and it's taking too long.

The PLRM, 1ed, says

> interrupt  (error)

> processes an external request to interrupt execution of a PostScript
> program. When the interpreter receives an interrupt request, it executes
> interrupt as if it were an error (i.e. it looks up the name 'interrupt' in
> errordict). Execution of interrupt is sandwiched between execution of
> two objects being interpreted in normal sequence.

> The precise nature of an external interrupt request depends on the en-
> vironment in which the PostScript interpreter is running. In typical
> environments, receipt of a control-C character from a serial communi-
> cation channel gives rise to the interrupt error. This permits a user to
> explicitly abort a PostScript computation. The default definition of 
> interrupt executes a stop.


I tried wrapping the drawing functions in a stopped context.

% The Main Loop
% - draw the object according to currrent parameters
% - enter menu loop
% - showpage
{
    {
        createtable findmaxmin sketch flushpage
    } stopped clear
    menu    
    showpage
} loop

But ctrl-C just kills the whole interpreter.

Is there a special mode or flag to enable /interrupt errors with GS?

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#1373

On Thursday, April 25, 2013 6:32:39 PM UTC-5, luser- -droog wrote:
> With my Mandelbrot explorer (https://code.google.com/p/xpost/downloads/detail?name=mandel2.ps),
> I'd like to be able to interrupt the drawing and return to the menu if 
> the resolution is too high and it's taking too long.
> 
> The PLRM, 1ed, says
> 
> > interrupt  (error)
> 
> > processes an external request to interrupt execution of a PostScript
> > program. When the interpreter receives an interrupt request, it executes
> > interrupt as if it were an error (i.e. it looks up the name 'interrupt' in
> > errordict). Execution of interrupt is sandwiched between execution of
> > two objects being interpreted in normal sequence.
> 
> > The precise nature of an external interrupt request depends on the en-
> > vironment in which the PostScript interpreter is running. In typical
> > environments, receipt of a control-C character from a serial communi-
> > cation channel gives rise to the interrupt error. This permits a user to
> > explicitly abort a PostScript computation. The default definition of 
> > interrupt executes a stop.
> 
> I tried wrapping the drawing functions in a stopped context.
> 
> 
> % The Main Loop
> % - draw the object according to currrent parameters
> % - enter menu loop
> % - showpage
> {
>     {
>         createtable findmaxmin sketch flushpage
>     } stopped clear
>     menu    
>     showpage
> } loop
> 
> But ctrl-C just kills the whole interpreter.
> 
> Is there a special mode or flag to enable /interrupt errors with GS?

I found something. But I don't know how to make use of it yet.

In psi/interp.c, I found this:

/*
 * Invoke the interpreter.  If execution completes normally, return 0.
 * If an error occurs, the action depends on user_errors as follows:
 *    user_errors < 0: always return an error code.
 *    user_errors >= 0: let the PostScript machinery handle all errors.
 *      (This will eventually result in a fatal error if no 'stopped'
 *      is active.)
 * In case of a quit or a fatal error, also store the exit code.
 * Set *perror_object to null or the error object.
 */
static int gs_call_interp(i_ctx_t **, ref *, int, int *, ref *);
int
gs_interpret(i_ctx_t **pi_ctx_p, ref * pref, int user_errors, int *pexit_code,
             ref * perror_object)
{

It looks like this `user_errors` parameter controls the behavior I'm talking about (I think). But I haven't traced it back out. I don't know where this function is called.

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#1374

luser- -droog wrote:

> With my Mandelbrot explorer
> (https://code.google.com/p/xpost/downloads/detail?name=mandel2.ps), I'd
> like to be able to interrupt the drawing and return to the menu if the
> resolution is too high and it's taking too long.
> 
> The PLRM, 1ed, says
> 
>> interrupt  (error)
> 
>> processes an external request to interrupt execution of a PostScript
>> program. When the interpreter receives an interrupt request, it executes
>> interrupt as if it were an error (i.e. it looks up the name 'interrupt'
>> in errordict). Execution of interrupt is sandwiched between execution of
>> two objects being interpreted in normal sequence.
> 
>> The precise nature of an external interrupt request depends on the en-
>> vironment in which the PostScript interpreter is running. In typical
>> environments, receipt of a control-C character from a serial communi-
>> cation channel gives rise to the interrupt error. This permits a user to
>> explicitly abort a PostScript computation. The default definition of
>> interrupt executes a stop.
> 
> 
> I tried wrapping the drawing functions in a stopped context.
> 
> % The Main Loop
> % - draw the object according to currrent parameters
> % - enter menu loop
> % - showpage
> {
>     {
>         createtable findmaxmin sketch flushpage
>     } stopped clear
>     menu
>     showpage
> } loop
> 
> But ctrl-C just kills the whole interpreter.
> 
> Is there a special mode or flag to enable /interrupt errors with GS?

Looking (not too deeply) into the Ghostscript sources reveals: 
it seems that capturing signals like this is mainly restricted to
events associated with the PostScript input (currentfile and friends).
I guess it is not trivial to enhance gs to treat CTRL-C as an interrupt 
error without fidling around with the kernel of ghostscript's ps interpreter
ans how it is hooked up to the operating system (to be precise: the OS 
abstraction level).

So I'd suggest you file a feature request at bugs.ghostscript.com.

Helge

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#1375

On Tuesday, April 30, 2013 11:35:23 AM UTC-5, Helge Blischke wrote:
> luser- -droog wrote:
> 
> > But ctrl-C just kills the whole interpreter.
> > 
> 
> > Is there a special mode or flag to enable /interrupt errors with GS?
> 
> 
> Looking (not too deeply) into the Ghostscript sources reveals: 
> it seems that capturing signals like this is mainly restricted to
> events associated with the PostScript input (currentfile and friends).
> I guess it is not trivial to enhance gs to treat CTRL-C as an interrupt 
> error without fidling around with the kernel of ghostscript's ps interpreter
> ans how it is hooked up to the operating system (to be precise: the OS 
> abstraction level).
> 
> 
> So I'd suggest you file a feature request at bugs.ghostscript.com.
> 
> 
> Helge

Thanks for the suggestion. Done.

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