From: "Alf P. Steinbach" <alfps@start.no>
To: help-gnu-emacs@gnu.org
Subject: Re: How to exit out of a function ? what is try-catch-throw in terms of Program Counter
Date: Mon, 05 Nov 2007 06:07:25 +0100 [thread overview]
Message-ID: <13it94l8vrcqfac@corp.supernews.com> (raw)
In-Reply-To: <cbjsi3ts4121gsand4qt18cure6sbupf28@4ax.com>
* David Thompson:
> On Sun, 21 Oct 2007 00:55:53 +0200, "Alf P. Steinbach"
> <alfps@start.no> wrote:
>
>> * gnuist006@gmail.com:
>
>>> NOTE: I am really afraid of try-catch-throw. I have never been
>>> able to understand it since it does not exist in C and I cant
>>> really visualize the construct in terms of C. <snip>
>> The closest equivalent in C would be a 'longjmp'. However, a C++
>> exception is more limited, in that it will only jump up the call chain,
>
> C longjmp/setjmp also is only guaranteed to work up the stack; the
> fact that _some_ implementations can work cross-stack and in
> particular cross-thread is not standard nor portable.
So?
But also, what on Earth do you mean by a cross-thread longjmp? I
implemented coroutines in terms of longjmp at the time that was popular,
so the concepts involved are not unfamiliar to me. Yet I fail to
envision what you could be talking about, especially as "fact". I think
perhaps you're talking about restoring the full context (registers etc)
of a moment in a thread's execution?
>> and it's more powerful, in that it will destroy local objects as it does
>> so. Also, if you use 'longjmp' in C++ you're practically doomed (unless
>> you use it to jump between co-routines with their own stacks), because
>> 'longjmp' doesn't destroy local objects.
>>
> Actually it's Undefined Behavior; a good quality C++ implementation
> CAN coordinate longjmp, and also pthreads cancellation, with
> exceptions to destruct locals cleanly -- but it's not required.
I don't know about ptheads cancellation, but other than that you're
right. Visual C++ coordinates longjmp with C++ stack unwinding. g++,
on the other hand, does not.
Cheers, & hth.,
- Alf
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
next prev parent reply other threads:[~2007-11-05 5:07 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-20 20:45 How to exit out of a function ? what is try-catch-throw in terms of Program Counter gnuist006
2007-10-20 20:57 ` gnuist006
2007-10-20 22:55 ` Alf P. Steinbach
2007-10-23 18:06 ` gnuist006
2007-10-23 19:53 ` Alf P. Steinbach
2007-11-04 23:02 ` David Thompson
2007-11-05 5:07 ` Alf P. Steinbach [this message]
2007-11-05 5:59 ` Alf P. Steinbach
2007-12-02 23:20 ` David Thompson
2007-12-02 23:51 ` Alf P. Steinbach
2007-10-21 1:08 ` Jim Langston
2007-10-21 2:30 ` Keith Thompson
2007-10-21 10:44 ` Kenny McCormack
2007-10-21 10:55 ` santosh
2007-10-21 12:26 ` Richard Heathfield
2007-10-21 22:35 ` Mark McIntyre
2007-10-21 12:09 ` Malcolm McLean
2007-10-21 15:23 ` Kenny McCormack
2007-10-21 15:54 ` santosh
2007-10-21 17:39 ` Malcolm McLean
2007-10-21 21:53 ` Kenny McCormack
2007-10-21 8:03 ` Malcolm McLean
2007-10-21 16:07 ` abhy
2007-10-21 17:43 ` santosh
2007-10-23 9:04 ` Joel Yliluoma
2007-10-23 16:33 ` Stefan Monnier
2007-10-23 16:44 ` gnuist006
2007-10-23 16:45 ` Victor Bazarov
2007-10-24 1:06 ` Stefan Monnier
2007-10-23 16:54 ` gnuist006
2007-10-23 17:14 ` Alf P. Steinbach
2007-10-24 1:09 ` Stefan Monnier
2007-10-24 0:02 ` Joel Yliluoma
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