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Date: Thu, 9 Dec 2004 18:03:59 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: Re: [Fwd: [gp AT familiehaase DOT de: sem_* functions in cygwin]]
Message-ID: <20041209170359.GE22056@cygbert.vinschen.de>
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References: <20041209164442 DOT GA25246 AT cygbert DOT vinschen DOT de> <0I8G00F7VS4BRS AT pmismtp01 DOT mcilink DOT com>
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On Dec  9 09:50, Mark Paulus wrote:
> So, does that mean that if process 1 opens a semaphore,
> process 2 also grabs it, then process 1 unlinks it, and then
> "reconnects" to it, that process 1 and process 2 do not have
> and cannot have the same semaphore anymore, even though
> they are using the same IPC_KEY?
> 
> (Or am I way confused/off base here)?

Only partially.  IPC_KEYs have nothing to do with it since we're talking
about *POSIX* semaphores, not *SYSV* semaphores.

Otherwise you're right.  After some process has called sem_unlink(), any
subsequent call to sem_open with the same sempahore name connects to a new
semaphore.


Corinna

> 
>   On Thu, 09 Dec 2004 17:44:42 +0100, Corinna Vinschen wrote:
> 
> >[Catching up on some older mails]
> 
> >> ----- Forwarded message from "Gerrit P. Haase" -----
> >> From: "Gerrit P. Haase" 
> >> To: cygwin ML
> >> Subject: sem_* functions in cygwin
> >> Date: Sun, 21 Nov 2004 22:48:20 +0100
> >> 
> >> Hi,
> >> 
> >> nearly all sem_* functions are available, but sem_unlock is missing,
> >> was there a problem implementing sem_unlock() or was it just missed
> >> by accident?
> >> 
> >> 
> >> Gerrit
> >> ----- End forwarded message -----
> 
> >I guess you're asking about sem_unlink().  It's not implemented so far
> >since named POSIX semaphores are implemented using named Windows semaphores. 
> >The SUSv3 description contains a pretty unfortunate implementation detail:
> 
> >  Calls to sem_open() to recreate or reconnect to the semaphore refer
> >  to a new semaphore after sem_unlink() is called.
> 
> >There's no way I know of, which allows to implement this using named
> >Windows semaphores.  At least not without adding a lot of annoying
> >bookkeeping overhead, possibly involving cygserver.
> 
> 
> >Corinna
> 
> >--
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-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

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