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 16:45 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2013Apr3.184544@mips.complang.tuwien.ac.at> (permalink)
References	(5 earlier) <urudnXczhs7nosXMnZ2dnUVZ_uCdnZ2d@supernews.com> <2013Apr2.175019@mips.complang.tuwien.ac.at> <YL6dnW-fLKgN18bMnZ2dnUVZ_tKdnZ2d@supernews.com> <2013Apr3.135744@mips.complang.tuwien.ac.at> <4-ednRv0asts1MHMnZ2dnUVZ_sadnZ2d@supernews.com>

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Well, it's not just you, it's all of your users.  And can you really
>write a tree node removal that can be restarted at any point?  I guess
>you could copy the whole tree and work on the copy.  Eww...

Yes, that would be a way, if I wrote tree removal code.  But I usually
don't use trees in memory, and certainly not for cases where nodes
need to be removed.  For on-disk (persistent) data structures, I would
do it exactly that way, exactly, because the writes can be interrupted
at any time.

>> 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. 
>
>I'm not sure that it is.  I'm not saying that you should terminate the
>system itself, but there may be no correct way to continue with a
>program.

Yes, maybe, but that's up to the programmer and the user to decide.

>>> and for interpreted code the cost can be zero.
>> 
>> How does that work?
>
>If there's a table of pointers then you can overwrite part of the
>table; if there's an interpreter pointer you can rewrite that when you
>return from the handler.

That's not a non-zero cost; a table of pointers is slower than
threaded code.  And if you want to patch the threaded code, you need
to ensure that there is always a pointer to the next instruction
available, which also has a cost, and I actually don't know how to do
it.

>Synchronous signals are another matter altogether.  I see no reason
>why those shouldn't be handled immediately.  The problem with
>asynchronous signals is that, by their very nature, they can happen in
>the middle of operations that you really want to be atomic.

Hmm, doing the THROW for synchronous signals from the signal handler,
and delaying it for asynchronous ones would be an option.  But delay
until when?

>> 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?
>
>A long time?  Why?  Maybe there's a bug.  In which case you don't want
>a catachable exception because that'll just make the program continue.
>I suspect you really want to return to the keyboard interpreter, in
>which case stopping immediately makes perfect sense.

The usual use of CATCH is to clean up things the program has messed
up, like restoring BASE or closing files.  Yes, the cleanup might run
into problems if the signal happened in the middle of the messing-up,
but that's extremely rare (I have not experienced it yet), and in the
other cases it's better to clean up than to stop immediately in the
messed-up state.

- 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
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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

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