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Date: Mon, 26 Mar 2001 16:52:23 +0200
From: Stelian Pop <stelian.pop@fr.alcove.com>
To: Nigel Gamble <nigel@nrg.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Use semaphore for producer/consumer case...
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Reply-To: Stelian Pop <stelian.pop@fr.alcove.com>
In-Reply-To: <20010323130722.A8916@come.alcove-fr> <Pine.LNX.4.05.10103231541010.6461-100000@cosmic.nrg.org>
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In-Reply-To: <Pine.LNX.4.05.10103231541010.6461-100000@cosmic.nrg.org>; from nigel@nrg.org on Fri, Mar 23, 2001 at 03:52:54PM -0800
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On Fri, Mar 23, 2001 at 03:52:54PM -0800, Nigel Gamble wrote:

> For the producer/consumer case, you want to initialize the semaphore to
> 0, not 1 which DECLARE_MUTEX(sem) does.  So I would use
> 
> __DECLARE_SEMAPHORE_GENERIC(sem, 0)

You're right that the DECLARE_MUTEX does not (entirely) do the job, 
but I set manually the value of sem->count:
> > 		atomic_set(&sem->count, -10);

> Then consumer could be:
> 		/* Wait for 10 items to be produced */
> 		for (i = 0; i < 10; i++)
> 			down(&sem);

IMHO, this will not work, because the producer could be issuing
more than one 'up(&sem)' at the time...

Stelian.
-- 
Stelian Pop <stelian.pop@fr.alcove.com>
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