Re: Difficulty with Brad Rodriguez' screenful

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Difficulty with Brad Rodriguez' screenful
Date	2013-04-03 11:57 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2013Apr3.135744@mips.complang.tuwien.ac.at> (permalink)
References	(6 earlier) <IfydnfIfReCdSNTMnZ2dnUVZ_r6dnZ2d@supernews.com> <2013Mar30.183505@mips.complang.tuwien.ac.at> <urudnXczhs7nosXMnZ2dnUVZ_uCdnZ2d@supernews.com> <2013Apr2.175019@mips.complang.tuwien.ac.at> <YL6dnW-fLKgN18bMnZ2dnUVZ_tKdnZ2d@supernews.com>

Show all headers | View raw

Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>> Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>>>Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>>>> Actually the CATCH has zero extra cost because it can catch THROWs
>>>> from signals.  Safepoints come from Java problems that Forth does
>>>> not have (at least not Gforth); no need for this complication in
>>>> Forth.
>>>
>>>That depends what caused the signal and what you're doing when it
>>>arrives: if you're in the middle of updating a linked list or
>>>releasing a queued lock, you're going to be in trouble.
>> 
>> Gforth has TRY...RESTORE...ENDTRY that can be useful in that
>> situation: Put the stuff that must happen between RESTORE and ENDTRY,
>> and write it in a way that is correct even if that part is started
>> several times, and only completes the last time.
>
>While I'm sure that this can work sometimes, I am extremely skeptical
>that it works in the general case.  If you rerite all your locking
>code to use this idiom I suppose it would work.

That's easy: Rewriting ... Done!

>But it's not just
>your code that's being interrupted: there may be system libraries
>involved.

Yes, we may be out of luck if there's a ^C in malloc.  But it's good
enough for now, better than terminating the program or the Forth
system.  One advantage of THROWing from the signal handler instead of
using a safe point is that it works for synchronous signals like stack
underflow; it would not do to try to continue execution until the safe
point is reached.

>> They appear pretty expensive to me.
>
>Not really: for compiled code it's just an occasional (usually
>in-cache) memory read,

At least once every loop iteration, no?

> and for interpreted code the cost can be zero.

How does that work?

Anyway, I am also thinking about the indirect costs, like not being
able to deal with synchronous signals, and therefore having to
generate extra code for checking for NULL pointer exceptions.

>Given that this is correct and works with all concurrent algorithms,
>it seems to me like a sensible compromise.

In Java maybe, in Forth, doubtful, even if we ignore synchronous
exceptions.  Say, you want to cover programs written for the
traditional Forth multi-tasking model, i.e., everything between two
PAUSEs or I/Os is atomic.  Then only PAUSE and I/Os would be safe
points.  But for a program that's not written for multitasking and
therefore does not use PAUSE, the program could run for a long time
without reacting to a ^C; and what's the typical use of ^C?

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2013: http://www.euroforth.org/ef13/

Back to comp.lang.forth | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-19 15:06 +0000
  Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 22:27 +0100
    Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 03:49 -0500
      Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-20 11:09 +0000
        Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 10:25 -0500
          Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 18:08 +0100
            Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 13:04 -0500
              Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 20:12 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-21 04:39 -0500
            Re: Difficulty with Brad Rodriguez' screenful albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-03-20 19:22 +0000
          Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-30 17:35 +0000
            Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-31 08:51 -0500
              Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 15:50 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-02 16:16 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-03 11:57 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-03 10:25 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-03 16:45 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-03 15:12 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-04 15:29 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-05 09:11 -0500
        Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-20 10:27 -0700
    Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-20 12:03 +0000
      Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 18:47 +0100
        Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-30 16:40 +0000
          Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-01 02:12 +0200
            Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-01 16:58 +0000
              Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-02 04:20 +0200
                Re: Difficulty with Brad Rodriguez' screenful "Elizabeth D. Rather" <erather@forth.com> - 2013-04-01 16:39 -1000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 14:15 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-02 21:12 +0200
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-04 13:58 +0000
              Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-02 04:17 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 15:35 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-02 16:36 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-03 04:10 +0200
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-03 04:03 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-03 21:14 +0200
            Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-03 16:13 +0000
              Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-03 11:54 -0500
              Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-03 22:24 +0200
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-04-04 11:53 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-04 18:13 +0200
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-04 15:53 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-04 22:11 +0200
                Re: Difficulty with Brad Rodriguez' screenful Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2013-04-04 21:35 +0100
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-04 23:06 +0200
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-04-05 10:57 +0000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-05 14:47 +0000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-05 14:28 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-06 03:35 +0200
                Re: Difficulty with Brad Rodriguez' screenful "Rod Pemberton" <do_not_have@notemailnotq.cpm> - 2013-04-08 23:50 -0400
                Re: Difficulty with Brad Rodriguez' screenful "Rod Pemberton" <do_not_have@notemailnotq.cpm> - 2013-04-08 23:49 -0400
                Re: Difficulty with Brad Rodriguez' screenful m.a.m.hendrix@tue.nl - 2013-04-05 02:49 -0700
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-05 14:55 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-05 22:05 +0200

csiph-web