To see an example of flock() in action, try running this script in a few consoles side by side.
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 "Going to sleep...\n";
print "Woken up...\n";
I just wanted to go through this because I see a lot of mistakes that people make with locking files, and show another way of making it all more secure. To make it even more secure, use a database :)
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