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Date: Mon, 18 Apr 2011 21:26:00 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: what does this cygserver error mean?
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On Apr 18 13:34, bob 295 wrote:
> (I'm in digest mode on this list so I can't thread my response easily.)
> 
> The cygserver is setup to run as a Windows service.  As far as I can tell the 
> cygserver is running when the error occurs.   What isn't clear from your 
> response is what causes the named pipe to cygserver to get created?  What 
> tears it down?    

Every single request to cygserver is basically a closed operation.
A function call like shmget opens the pipe, writes a request block,
reads the reply from cygserver and closes the pipe.

> 
> In my test the sequence of each Send/Receive/Reply message pass involves these 
> steps:  
> 1) the sender creates the shared memory and then attaches to for the purpose 
> of writing a message.    
> 2) The receiver gets passed the shmid (via a named pipe) and attaches for the 
> purpose of reading the message.   
> 3) The receiver will respond by writing into same shared memory area upon 
> which it will detach.

Wouldn't it be simpler to use POSIX shared memory for that?  shm_open
allows to specify a named shared memory which all applications of a
project can share without having to use IPC to transmit the name (aka
"shmid") of the shared region.  On Cygwin it also drops the requirement
to use cygserver.

> I have a script which is repeatedly sending a 1k message (up to 10 times).  
> The error isn't consistently happening but when it does it appears to happen 
> on the first message pass.

If you could create a very simple, self-contained testscase in plain C,
I'd take a look.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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