Re: What's up with our stdout?
- From: Andrew Reilly <andrew-freebsd@xxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 26 Jun 2006 14:07:54 +1000
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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