Shared/exclusive (rw) locks

ngl ngl at
Tue Jul 6 02:55:53 PDT 2004

----- Original Message ----- 
From: "Tim Robbins" <tjr at>
To: "ngl" <ngl at>
Cc: <freebsd-stable at>
Sent: Tuesday, July 06, 2004 1:17 PM
Subject: Re: Shared/exclusive (rw) locks

> On Tue, Jul 06, 2004 at 12:45:27PM +0600, ngl wrote:
> > That means, freebsd stable has no spin rwlocks ?
> Right. Reader-writer spinlocks would not be very useful in FreeBSD 4;
> only one thread can be running in the kernel at once

Forgive for my importunity, but what about smp ?

> , the only opportunity
> you'd have to share reader locks would be if you slept while holding a
> spinlock, which is a bad idea (and not permitted by FreeBSD 5 or Linux).
> If you want -rwlocks, you'll have to use lockmgr() (which is a sleep
> Tim
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