Date: Wed, 13 Dec 2006 09:23:23 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: David Xu <davidxu@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: close() of active socket does not work on FreeBSD 6 Message-ID: <Pine.GSO.4.64.0612130918140.13170@sea.ntplx.net> In-Reply-To: <200612132010.49601.davidxu@freebsd.org> References: <32874.1165905843@critter.freebsd.dk> <Pine.GSO.4.64.0612121543220.8780@sea.ntplx.net> <200612132010.49601.davidxu@freebsd.org>
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[CC trimmed] On Wed, 13 Dec 2006, David Xu wrote: > On Wednesday 13 December 2006 04:49, Daniel Eischen wrote: >> >> Well, if threads waiting on IO are interruptable by signals, >> can't we make a new signal that's only used by the kernel >> and send it to all threads waiting on IO for that descriptor? >> When it gets out to actually setup the signal handler, it >> just resumes like it is returning from an SA_RESTART signal >> handler (which according to another posting would reissue >> the IO command and get EBADF). > > Even if you have implemented the close() with the interruption, another > thread openning a file still can reuse the file handle immediately, > according to specifications, the lowest free file handle will be returned, > if SA_RESTART is used, the interrupted thread restart the syscall, > it will be using a wrong file, I think even if we have implemented the > feature in kernel, useland threads still has serious race to fix. If you use a special signal that is only used for this purpose, there is no reason you have to try the IO operation again. You can just return EBADF. Anyway, this was just a thought/idea. I don't mean to argue against any of the other reasons why this isn't a good idea. -- DE
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