Date: Mon, 26 Jun 2006 14:07:54 +1000 From: Andrew Reilly <andrew-freebsd@areilly.bpc-users.org> To: freebsd-arch@freebsd.org Subject: Re: What's up with our stdout? Message-ID: <20060626040754.GA30475@duncan.reilly.home> In-Reply-To: <20060625214021.GJ82074@funkthat.com> References: <20060625011746.GC81052@duncan.reilly.home> <20060625214021.GJ82074@funkthat.com>
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On Sun, Jun 25, 2006 at 02:40:21PM -0700, John-Mark Gurney wrote: > Andrew Reilly wrote this message on Sun, Jun 25, 2006 at 11:17 +1000: > > One interesting problem that I found yesterday was that NetBSD > > have added a "-l" option to cat, which is supposed to apply an > > exclusive advisory lock with fcntl to the the output file, and > > wait until that succeeds: > > http://netbsd.gw.com/cgi-bin/man-cgi?cat++NetBSD-current > > That seems like a pretty useful idea, > > because it means that you can have parallel make jobs all > > contributing to a log file or the like (with cat -l >> foo.log), > > without getting in eachothers' way. > > Why not use: > lockf -k foo.log cat >> foo.log > > Should do the same thing... Not only should it, I've just checked and discovered that it does. So I'll make up the appropriate tweak to NetBSD's Makefiles, and suggest on the mailing lists that they think about incorporating it, as it's ostensibly a more general and useful way to do it. This does make me wonder, though, why this _does_ work, given Bruce's explanation of why the nbcat code doesn't... Hmm. lockf.c uses open(...,|O_EXLOCK), rather than fcntl(). Any particular reason why that should behave differently? Cheers, -- Andrew
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