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Date: Mon, 28 Aug 2006 14:27:16 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: cygserver blocking on semctl(SETVAL) call
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On Aug 25 11:21, Ethan Tira-Thompson wrote:
> [Slightly modified from version previously sent on cygwin-developers,  
> who suggest this is a better forum for discussion]
> 
> I've discovered what I believe to be a internal deadlock issue in  
> cygserver.
> 
> I have a piece of code:
> void SemaphoreManager::setValue(semid_t id, int x) const {
> 	semun params;
> 	params.val=x;
> 	cout << "SEMCTL..." << flush;
> 	if(semctl(semid,id,SETVAL,params)<0) {
> 		perror("ERROR: SemaphoreManager::setValue (semctl)");
> 		exit(EXIT_FAILURE);
> 	}
> 	cout << "done" << endl;
> }
> 
> This is part of a function which gets called a number of times  
> throughout the life of the program.  It works just fine up until one  
> particular call (with x=0) which reliably causes it to block between  
> the two cout's.  Not just my program either -- all IPC is blocked at  
> this point.  [...]
> Our code can be checked out from CVS, but before running you'll need  
> to increase the semmns and semmsl parameters as described in step 5:
> http://www.cs.cmu.edu/~tekkotsu/cygwin-install.html
> [...]

This sounds pretty strange since from the source code I can't see any
chance that semctl(SETVAL) could hang indefinitly.  However, as
mentioned on cygwin-developers, please provide a simple, short, concise,
standalone testcase, possibly in plain C, which builds and shows the
problem OOTB.  The problem should be isolated to the minimum of code
necessary to get the hang, if possible.  I really don't have time nor
exactly fun to dive into a foreign complex project.


Corinna

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

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