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Date: Mon, 06 Feb 2006 07:00:24 -0700
From: Eric Blake <ebb9 AT byu DOT net>
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To: Sudhahar <jsudha80 AT gmail DOT com>
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Subject: Re: Cygwin fork implementation
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According to Sudhahar on 2/6/2006 5:33 AM:
> Hi,
>    In Cygwin fork code the statement
> 
> int res = setjmp (grouped.ch.jmp);
>   if (res)
>     res = fork_child (grouped.ch.parent, grouped.first_dll, grouped.load_dlls);
>   else
>     res = fork_parent (grouped.ch.parent, grouped.first_dll,
> grouped.load_dlls, esp, grouped.ch);
> 
> avoids the fork being called repeatedly by the created process of
> parent. Can anyone tell me how this actually happens. Thanks in
> advance for your time and comments.

If you are asking how setjmp works, it is not cygwin specific.  Any good
systems C programming book should give you more details, or you can read
what POSIX says:
http://www.opengroup.org/onlinepubs/009695399/functions/setjmp.html.

setjmp() is one of those MAGIC functions, that when paired with the
longjmp() in fork_parent(), returns 2 distinct values at different points
during execution.

You may also be interested in
http://cygwin.com/cgi-bin/cvsweb.cgi/src/winsup/cygwin/how-cygheap-works.txt?rev=1.5&content-type=text/x-cvsweb-markup&cvsroot=src

- --
Life is short - so eat dessert first!

Eric Blake             ebb9 AT byu DOT net
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