Date: Thu, 10 Dec 2009 00:24:28 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, Jilles Tjoelker <jilles@stack.nl>, John Baldwin <jhb@FreeBSD.org> Subject: Re: svn commit: r200274 - head/lib/libc/gen Message-ID: <alpine.BSF.2.00.0912100023220.23303@fledge.watson.org> In-Reply-To: <4B1FAC12.6080907@cs.duke.edu> References: <200912082048.nB8Km6aP099420@svn.freebsd.org> <200912081645.37356.jhb@freebsd.org> <20091208221028.GA57735@stack.nl> <200912081742.58162.jhb@freebsd.org> <4B1FAC12.6080907@cs.duke.edu>
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On Wed, 9 Dec 2009, Andrew Gallatin wrote: > John Baldwin wrote: > >> The fact that we don't fail attempts to use pshared outright is probably >> dubious. They cannot possibly work as currently implemented aside from >> fork() since the structure embeds a file descriptor and file descriptor >> indices are a per-process namespace, not a global namespace. > > FWIW, this is what confused me. It tends to be kind of a land-mine, since > programs can be ported from Linux, and appear to work at first for casual > use. If we don't support pshared, we should return an error from sem_init() > to make it obvious. > > Also, perhaps the sem_init() man page should mention sem_open(), since that > seems to be the only way to really share a semaphore between processes on > FreeBSD. It's beginning to sound like our POSIX semaphores should be behaving more like umtx, which requires only a shared page, and less like file descriptors. Of course, that would make the global namespace more tricky... Robert N M Watson Computer Laboratory University of Cambridge
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