Re: How to apply flock

Hi,
you can use flock in this way

#!/usr/bin/perl -w
use strict;
use Fcntl ':flock'; # import LOCK_* constants

sub lock {
    flock(FH,LOCK_EX);
    # and, in case someone appended
    # while we were waiting...
    seek(FH, 0, 2);
}

sub unlock {
    flock(FH,LOCK_UN);
}

my $filename = "plain-db.pdb";

open(FH, ">>$filename")
    or die "Can't open file ($filename): $!";

lock();

# do what ever you want with it 

unlock();
[download]

Maybe this can help you.

Comment on Re: How to apply flock Download Code

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Re: Re: How to apply flock
by no_slogan (Deacon) on Nov 25, 2002 at 07:04 UTC

lock();
# do what ever you want with it 
unlock();
[download]

If "whatever you want" involves tieing a DB_File, you're in for trouble. Some versions of BerkeleyDB close the file and reopen it, which loses the lock for you. This took me a lot of pain and agony to discover, but fortunately not too much data was corrupted before I figured it out.

Using a separate lock file is good. The mod_perl guide is good. Heed the other monks.

Update: If you close the same file you lose the lock, even if you open it through a different filehandle and close that one. Locks exist at the inode level, not the filehandle level.

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[d/l]

Re: Re: Re: How to apply flock

by Chief of Chaos (Friar) on Nov 25, 2002 at 07:48 UTC

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Re: Re: How to apply flock
by PodMaster (Abbot) on Nov 25, 2002 at 12:21 UTC

That is the classic perl flock boo-boo. You should never "unlock", just close the file, and the lock will go away.

Also, do you really need a lock subroutine?

I didn't respond to this the other day in hopes that somebody else would, and much to my suprise, nobody paid attention.

MJD says you can't just make shit up and expect the computer to know what you mean, retardo!
** The Third rule of perl club is a statement of fact: pod is sexy.

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