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Date: Thu, 16 Sep 2004 13:27:28 -0400
From: Chet Ramey <chet AT caleb DOT ins DOT cwru DOT edu>
To: cgf AT cygwin DOT com
Subject: Re: Bash returns incorrect process status
Cc: chet AT po DOT cwru DOT edu, pierre DOT humblet AT ieee DOT org, cygwin AT cygwin DOT com,
   ronald AT landheer DOT com
Reply-To: chet AT po DOT cwru DOT edu
References: <41499B4A DOT 207AC15F AT ieee DOT org> <040916151300 DOT AA27319 DOT SM AT caleb DOT ins DOT cwru DOT edu> <20040916154409 DOT GC681 AT trixie DOT casa DOT cgf DOT cx>
In-Reply-To: Message from cgf@cygwin.com of Thu, 16 Sep 2004 11:44:09 -0400 (id <20040916154409.GC681@trixie.casa.cgf.cx>)
Message-ID: <040916172728.AA27372.SM@caleb.ins.cwru.edu>
Read-Receipt-To: chet AT po DOT CWRU DOT Edu
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> Is there some reason why we aren't discussing this on the mailing
> list?

Which mailing list?  I'm not on the cygwin list.

> >POSIX shells are required to remember at least CHILD_MAX (but
> >optionally more) process statuses.  There is a gray area about whether
> >or not the user can query the status of those processes, implying that
> >once the status of a background or foreground job has been reported,
> >its status, and the status of its constituent processes, can be
> >discarded, but those rules are hard to decipher.
> 
> Are you saying that waitpid should be able to return the status of an
> exited process when it is called repeatedly?  I've never seen anything
> like that.  I thought that once you'd done a wait the process was
> unzombified, it goes away, and it is unavailable for future querying.

No.  The portion of the POSIX spec describing the shell's behavior is
independent of the exact function used to query a process's status.  It
says the shell has to remember.  It doesn't mention waitpid(), nor does
it need to.

You're assuming that the shell just does a waitpid() whenever it needs to
get a particular process's status.  No shell does it that way.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
( ``Discere est Dolere'' -- chet )
						Live...Laugh...Love
Chet Ramey, ITS, CWRU    chet AT po DOT cwru DOT edu    http://tiswww.tis.cwru.edu/~chet/

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