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Cc: Pawel Jakub Dawidek <pjd@freebsd.org>, Robert Watson <rwatson@FreeBSD.org>,
	current@freebsd.org
Subject: Re: [RFC] locking.9
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Julian Elischer wrote:

> 
> ok so how about I commit this to get us started and the nroff and
> locking experts can take it from there.
> 

The first table I think may look like this 
(from quick reading.. but I may be wrong):


     The following table shows what you can and can not do if you hold one of
     the synchronisation primatives discussed here: (someone who knows what
     they are talking about should write this table)

           You have:  You want: Spin_mtx  Slp_mtx sx_lock rw_lock sleep
           SPIN mutex           ok        no      no      no      no-3
           Sleep mutex          ok        ok-1    no      ok      no-3
           sx_lock              ok        no      ??      no      ok-4
           rw_lock              ok        no      no      ok-2    no-3

     *1 Recursion is defined per lock. lock order is important.

     *2 readers can recurse tough writers can not. lock order is important.

     *3 There are calls atomically release this primative when going to sleep
     and reacquire it on wakeup (e.g.  mtx_sleep(), rw-sleep() and
     msleep_spin).()

     *4 One can also use sx_sleep() which atomically release this primative
     when going to sleep and reacquire it on wakeup.