Date: Mon, 15 Feb 2016 19:56:21 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Martin Simmons <martin@lispworks.com> Cc: vangyzen@FreeBSD.org, threads@FreeBSD.org, arch@FreeBSD.org Subject: Re: libthr shared locks Message-ID: <20160215175621.GU91220@kib.kiev.ua> In-Reply-To: <201602151735.u1FHZXKV006190@higson.cam.lispworks.com> References: <20151223172528.GT3625@kib.kiev.ua> <56BE69B8.9020808@FreeBSD.org> <20160213143815.GB91220@kib.kiev.ua> <201602151417.u1FEHKwL003392@higson.cam.lispworks.com> <20160215144410.GT91220@kib.kiev.ua> <201602151735.u1FHZXKV006190@higson.cam.lispworks.com>
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On Mon, Feb 15, 2016 at 05:35:33PM +0000, Martin Simmons wrote: > >>>>> 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. A process which has the page where the initialized pthread_barrier_t is located, must be able to operate on the barrier. Now, look at your scheme. One process which executed pthread_barrier_init(), performed what you proposed. What should do the pthread_barrier_wait() call in another process, which shares the 'barrier' with the first process, but does not share the whole address space ? After your pthread_barrier_init() executed, barrier contains the address of the object (off-page) in the other address space, for that process.
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