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From: John Baldwin <jhb@freebsd.org>
To: Craig Rodrigues <rodrigc@crodrigues.org>
Date: Thu, 8 Dec 2005 09:56:35 -0500
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Cc: freebsd-arch@freebsd.org
Subject: Re: [RFC] Implement cv_wait_nolock(),
	for emulation of SGI's sv_wait()
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On Wednesday 07 December 2005 05:43 pm, Craig Rodrigues wrote:
> Hi,
>
> As part of the XFS for FreeBSD project, Alexander Kabaev
> implemented a cv_wait_nolock() function for compatibility
> with SGI's sv_wait() call:
> http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=3D0650&db=3Dm=
an&fna
>me=3D/usr/share/catman/p_man/catD/SV_WAIT.z
>
> sv_wait() waits on a synchronization variable, the lock must be held
> before the call is entered, but the lock is not held when sv_wait() is
> exited.
>
> Is this patch OK to go into FreeBSD?
> Comments?

As I said on IRC, I'm not a big fan of this or PDROP, but PDROP is in the=20
tree.  Note that you could implement sv_wait() using the existing primitive=
s=20
via:

sv_wait()
{
	cv_wait()
	mtx_unlock()
}

If you do stick with cv_wait_nolock(), _please_ don't duplicate a whole bun=
ch=20
of code by implement cv_wait() like so:

cv_wait()
{
	cv_wait_nolock()
	mtx_lock()
}

Note that currently you have a bug in the cold || panicstr case in that the=
=20
function doesn't drop the lock.

=2D-=20
John Baldwin <jhb@FreeBSD.org> =A0<>< =A0http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" =A0=3D =A0http://www.FreeBSD.org