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Date: Mon, 15 Feb 2016 17:35:33 GMT
Message-Id: <201602151735.u1FHZXKV006190@higson.cam.lispworks.com>
From: Martin Simmons <martin@lispworks.com>
To: Konstantin Belousov <kostikbel@gmail.com>
CC: vangyzen@FreeBSD.org, threads@FreeBSD.org, arch@FreeBSD.org
In-reply-to: <20160215144410.GT91220@kib.kiev.ua> (message from Konstantin
 Belousov on Mon, 15 Feb 2016 16:44:10 +0200)
Subject: Re: libthr shared locks
References: <20151223172528.GT3625@kib.kiev.ua> <56BE69B8.9020808@FreeBSD.org>
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>>>>> On Mon, 15 Feb 2016 16:44:10 +0200, Konstantin Belousov said:
> 
> On Mon, Feb 15, 2016 at 02:17:20PM +0000, Martin Simmons wrote:
> > 
> > Also, a general question: why not use some flag in the barrier (and other
> > objects) to indicate pshared, removing the need for __thr_pshared_offpage
> > except in init?
> 
> But where would I keep the object ? All that I have with the current
> ABI is a single pointer, which de facto behaves like the flag which you
> proposed. It is either real pointer or (if set to some specific value
> impossible for a valid pointer) there is an offpage.

I'm probably missing something, but I was thinking pthread_barrier_init would
do something like

if ( attr is PTHREAD_PROCESS_PRIVATE ) {
   bar = calloc(1, sizeof(struct pthread_barrier));
   pshared = 0;
} else {
   bar = __thr_pshared_offpage(barrier, 1);
   pshared = 1;
}
bar->psharedflag = pshared;
*barrier = bar;

Then pthread_barrier_destroy would use the psharedflag slot to decide how to
free it and pthread_barrier_wait would need no changes.