Date: Fri, 12 Nov 2010 10:17:28 -0500 From: John Baldwin <jhb@freebsd.org> To: Jilles Tjoelker <jilles@stack.nl> Cc: src-committers@freebsd.org, David Xu <davidxu@freebsd.org>, svn-src-user@freebsd.org Subject: Re: svn commit: r215071 - in user/davidxu/libthr: include lib/libc lib/libc/gen lib/libc/stdio lib/libthr lib/libthr/thread Message-ID: <201011121017.28819.jhb@freebsd.org> In-Reply-To: <20101112131941.GA57806@stack.nl> References: <201011100127.oAA1Rmrh069656@svn.freebsd.org> <20101112131941.GA57806@stack.nl>
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On Friday, November 12, 2010 8:19:42 am Jilles Tjoelker wrote: > On Wed, Nov 10, 2010 at 01:27:48AM +0000, David Xu wrote: > > Author: davidxu > > Date: Wed Nov 10 01:27:48 2010 > > New Revision: 215071 > > URL: http://svn.freebsd.org/changeset/base/215071 > > > Log: > > Convert pthread_mutex_t and pthread_cond_t to structure based instead of > > pointer type, this allows us to support process-shared. > > Very nice. > > Apart from supporting process-shared, this also helps avoid the "array > of synchronization objects" anti-pattern (false sharing). It is not so > bad for the old struct pthread_mutex which is 64 bytes on i386, but in > other cases one cache line may contain parts of multiple unrelated > synchronization objects. > > In this regard, it would be better for stdio to allocate > struct { FILE file; pthread_mutex_t lock; } > rather than separate FILEs and locks. Note that stdio already does this. It currently expands 'pthread_mutex_t' to avoid namespace pollution in <stdio.h>, but it does embed the pthread_mutex_t in FILE directly already. This does mean that changing pthread_mutex_t will change the ABI of FILE, but I think it is not an incompatible change as it should not affect the "public" fields accessed via macros. -- John Baldwin
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