Hi there, I'm very new to the site, and I'm a little overwhelmed :-) I was looking around and see that the discussions are quite active, so I'm hoping someone could help .. please:-) I've been coding perl for sometime now, but there has always been one thing that gets my goat .. and that is flocking.

When I first began I used

flock(file,2);

now I use: 

use Fcntl ':flock';
flock(file,LOCK_EX);
seek file, 0, 0;

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Plucked pretty much from the perl man pages. I really try to read everything I can before asking but this one has got me stumped. Just when I figured I got it down pat, it seems I am running into to problems.

creating a simple read and write counter to demonstrate the flocking abilities, I see that every so often, the file is cleared. On every instance I read & write to the file I use the second method above, except for reading I used a shared_lock (LOCK_SH) When I change the shared lock to exclusive, it seems to run better, but then it happens again.

Searching around I came apon this page: From the Monastery and the last reply added by user KM has got me thinking. It seems reasonable, but I have to say I'm confused.

This method that the user speaks of: 

#!/usr/bin/perl -wT
use Fcntl qw(:flock);
my $file = 'test_lock.txt';
my $SEMAPHORE = $file . '.lck';
open(S, ">$SEMAPHORE") or die "$SEMAPHORE: $!";
flock(S, LOCK_EX) or die "flock() failed for $SEMAPHORE: $!";
open (FH, ">>$file") or die "Can't open $file: $!";
print "About to write\n";
print FH "I have written ($$)\n";
print "Written\n";
close FH;
print "Going to sleep...\n";
sleep 10;
print "Woken up...\n";
close S;

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... does this lock the file being written to, because it is hanging when the other file is locked arg :( Should I use this method? Is it more secure?

Please help, I'm still learning everday, and this is one question I would like to resolve and get a good nights sleep :-)

Thank you sincerly for any replies.

In reply to Flocking .. insanity is close. by Anonymous Monk

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