Date: Thu, 7 Apr 2005 20:09:33 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Zera William Holladay <zholla1@uic.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: Kernel [memory] tweaking question Message-ID: <20050407200537.Q29189@fledge.watson.org> In-Reply-To: <Pine.GSO.4.58.0504070907040.18583@icarus.cc.uic.edu> References: <42518AC9.5070208@comcast.net> <3.0.1.32.20050405052601.00ab4388@pop.redshift.com> <20050407083639.GD57256@cirb503493.alcatel.com.au> <Pine.GSO.4.58.0504070907040.18583@icarus.cc.uic.edu>
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On Thu, 7 Apr 2005, Zera William Holladay wrote: > On Thu, 7 Apr 2005, Peter Jeremy wrote: >> These are all reasonably well documented in sys/conf/NOTES. If you >> want more detail, try a SystemV-oriented Unix book >> >> Close - they only control SystemV shared memory. Sane shared memory >> is available via mmap(2). SystemV semaphores are controlled via >> SEMxxx options. Posix semaphores are listed as 'experimental'. > > Is there any chance that POSIX semaphores will be anything other than > experimental in the future, or is there no interest? Further, the man > page indicates that the FreeBSD, POSIX semaphore implementation is not > capable of supporting multiple process semaphores. I saw a similar note > on a Linux man page. I think this is a shame, since POSIX semaphores > seem to be well designed (from a user point of view) compared to SYSV > semaphores, which are a total mess. I haven't read the man page recently, but I've used our POSIX semaphores in an inter-process form successfully, and fixed a bug in them relating to fork relatively recently. My understanding is that some issues may remain in the handling of error cases when semaphore support isn't present -- whether the process is terminated, or gets ENOSYS, depending on whether the program is linked against libpthread or not. The fix for fork() handling will be present in 5.4-RELEASE. Robert N M Watson
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