Date: Wed, 17 Feb 2016 18:16:12 +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: <20160217161612.GL91220@kib.kiev.ua> In-Reply-To: <201602161617.u1GGHkil023634@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> <20160215175621.GU91220@kib.kiev.ua> <201602161617.u1GGHkil023634@higson.cam.lispworks.com>
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On Tue, Feb 16, 2016 at 04:17:46PM +0000, Martin Simmons wrote: > >>>>> On Mon, 15 Feb 2016 19:56:21 +0200, Konstantin Belousov said: > > > > 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. > > Ah, sorry, I understand now (the init functions are called before any > sharing). Well, the memory is either already shared between processes, or it should become shared before other process may operate on the object carried by the memory. It is that pthread_mutex_init() must be called before any other pthread_mutex_*() functions, but only once globally. > > How should the destroy functions be used by the processes? I.e. should only > the "last" process call destroy or can every process call it? Hm, this is a good observation. pthread_mutex_destroy() must be called only by last process, i.e. no other pthread_mutex_* calls are allowed for the object after the _destroy() was called. What this means for my implementation, is that processes other than the _destroy() caller keep the record in the pshared cache, and this needs fixing. For now, I added a mechanism which scans the whole hash and re-checks the validity on any object destroy. This can be optimized, e.g. by doing the scan only each N calls to _destroy(), or by scanning only the same hash chain, or by not doing this at all. I think it is an acceptable compromise for now. A specific test for the case is at https://www.kib.kiev.ua/kib/pshared/pthread_shared_destroy.c Updated patch https://www.kib.kiev.ua/kib/pshared/pshared.4.patch
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