Can't get flock() to work. Please help...

alain_desilets has asked for the wisdom of the Perl Monks concerning the following question:

I have read the excellent tutorial:

http://www.perlmonks.org/?node_id=7058

But somehow I can't get it to work. For example, here is a little script that (a) opens a file, (b) puts an exclusive lock on it, (c) closes the file (hence in theory releasing the lock), then (d) reopens the file and finally (e) tries to put another exclusive lock on it.

use strict;

my $fpath = 'blah.dat';
open(FILEHANDLE_1, ">", $fpath);
print "Opened file '$fpath' into FILEHANDLE_1.\n";

flock(FILEHANDLE_1, 2);
print "Put exclusive lock on FILEHANDLE_1\n";

close(FILE_HANDLE_1);
print "Closed FILEHANDLE_1. It should now be possible to put an exclus
+ive lock on file '$fpath'\n";

open(FILEHANDLE_2, ">", $fpath);
print "Opened file '$fpath' into FILEHANDLE_2.\n".
      "Will now try to put an exclusive lock on it.\n";

flock(FILEHANDLE_2, 2);
print "Successfully put exclusive lock on FILEHANDLE_2\n";
[download]

The problem is that the last line is never printed at all! In other words, the script is not able to secure the second lock, eventhough the first lock should have been released by the closing of FILEHANDLE_1.

What am I doing wrong? Note that I am running this on Windows 7. Could this be a problem with that OS? Does this script run fine on Linux? Thx. Alain Désilets

Comment on Can't get flock() to work. Please help... Download Code

Replies are listed 'Best First'.
Re: Can't get flock() to work. Please help... by toolic (Bishop) on Aug 30, 2011 at 15:41 UTC
What am I doing wrong? You're not using warnings (use strict and warnings). The problem also exists on linux. Here is what you would get with warnings: `Name "main::FILE_HANDLE_1" used only once: possible typo at` [download] See also: What shortcuts can I use for linking to other information?: File Locking	[reply] [d/l]
Re^2: Can't get flock() to work. Please help... by alain_desilets (Beadle) on Aug 30, 2011 at 19:26 UTC
Cool! I have been using strict for years, but had never heard of warnings. I'll add that to my standard boilerplate code for Perl scripts. -- Alain	[reply]
Re^3: Can't get flock() to work. Please help... by GrandFather (Saint) on Aug 31, 2011 at 02:49 UTC
Then change you file open boilerplate to: `open my $fileIn, '<', $filename or die "Can't open $filename: $!";` [download] which uses the three argument form of open (you werre already actually, but just making it explicit), uses lexical file handles (with strict that would have caught your typo too) and reports open errors. True laziness is hard work	[reply] [d/l]
Re: Can't get flock() to work. Please help... by DanielSpaniel (Scribe) on Aug 30, 2011 at 15:30 UTC
You have your close "FILE_HANDLE_1" spelled incorrectly. It should be "FILEHANDLE_1".	[reply]
Re^2: Can't get flock() to work. Please help... by alain_desilets (Beadle) on Aug 30, 2011 at 15:36 UTC
God I feel silly! Sorry about that. Alain	[reply]