#!/usr/bin/perl -w
$|=1;		   		## Don't buffer output
use CGI;
use Fcntl qw(:flock);
my $file = 'tmp/test_lock.txt';
my $SEMAPHORE = $file . '.lck';
# Output Early for debug
my $q = new CGI;
print $q->header;
my $x;
for ($x = 0; $x < 50; $x++)
 {
 print "<!-- FORCE STREAM -->\n";
 }

for ($x = 0; $x < 10; $x++)
 {
 print "Line $x<BR>\n";
 sleep 1;
 }
print "Getting lock<br>\n";
open(S, ">$SEMAPHORE") or die "$SEMAPHORE: $!";
flock(S, LOCK_EX) or die "flock() failed for $SEMAPHORE: $!";
print "Got lock<br>\n";
my $l;
my @in;
if (open (FH, "$file")) {
  @in = <FH>;
  close FH;
  foreach $_ (@in) {
	if ($_ =~ /(.*): I have/) {
		$l = $1;
	}
  }
  $l = $l+1 if $l;
} else {
 print "Can't open $file: $!";
}

$l = 1 unless $l;
push (@in,"$l: I have written ($$) flock\n");
open (FH, ">$file") or die "Can't open $file: $!";
print "About to write<br>\n";
print FH @in;
print "Written: $l<br>\n";
close FH;
print "Going to sleep...\n";
for ($x = 0; $x < 50; $x++)
 {
 print "$x ... <!-- FORCE STREAM --><br>\n";
 sleep 1;
 }
print "Woken up...<br>\n";
close S;