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From: John Baldwin <jhb@FreeBSD.org>
To: "M. Warner Losh" <imp@bsdimp.com>
Date: Thu, 16 Sep 2004 21:52:41 -0400
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Subject: Re: cvs commit: src/sys/dev/md md.c
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On Thursday 16 September 2004 08:59 pm, M. Warner Losh wrote:
> In message: <414A109E.4080601@samsco.org>
>
>             Scott Long <scottl@samsco.org> writes:
> : Or just use a semaphore.
>
> Or a condition variable.

That doesn't help, a condition variable doesn't have state like a semaphore.  
The correct fix is to do this:

thread A
----------
	mtx_lock();
	adjust_state();
	mtx_unlock();
	wakeup();

thread B
---------
	mtx_lock();
	while (state_still_needs_sleep())
		msleep(...)
	mtx_unlock()

Proving that there is no race is left as an exercise to the reader. :)

-- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org