dom at happygiraffe.net
Tue Dec 13 16:38:02 GMT 2005
On Tue, Dec 13, 2005 at 04:24:51PM +0000, Simon Wistow wrote:
> We have a farm of machines which will have access to a file. We only
> want one of the machines accessing that file at once - if a process
> cannot get a lock on the file then it should exit immediately otherwise
> it shoudl write the necessary number of times to the file and then exit.
> Of course flock() doesn't work across NFS. Is the only solution to this
> a flock daemon?
If you're in Perl, flock() is probably implemented using fcntl(), which
is supported over NFS. Run strace over a test script to verify.
If it's not, then you need to do jiggery pokery with lockfiles. This
involves, IIRC, creating a temp file using your hostname, pid, current
time, and $i++. You then have to call link() and then stat() in order
to check that the number of links is correct. Or something like that...
Basically you want to look like a Maildir.
This seems to describe what I'm thinking of:
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