Is there a way in Perl to tell if a Perl process in Windows is using a specific file?

Question

Background information:

I have a Perl script converted to a EXE file, script.exe, that runs on Windows. Script.exe reads and will update at times to/from a configuration file, config.ini.

Script.exe is either executed with a command-line argument specifying location of the config.ini file. Or it can be run without a command-line argument and will default to the default location for the config.ini file.

Goal:

Prevent script.exe from being executed more than once using the same config.ini file.

How can I do this?

Am I reading it wrong, or are you simply looking for `flock`? — ikegami, Nov 26 '13 at 20:20
@mpapec, Yes, though it creates mandatory locks rather than advisory locks — ikegami, Nov 26 '13 at 20:22
perhaps perl can read from Process Explorer http://stackoverflow.com/questions/15708/how-can-i-determine-whether-a-specific-file-is-open-in-windows — mpapec, Nov 26 '13 at 20:23
@ikegami ok, and all combinations work? excl/shared | blocking/nonblocking? — mpapec, Nov 26 '13 at 20:24
@mpapec, Yes. Technically, Windows even has another level of sharing flock can't control (delete). — ikegami, Nov 26 '13 at 20:26

ikegami · Answer 1 · 2013-11-26T20:34:28.777

2

Use flock on the config file.

use Fcntl qw( LOCK_EX LOCK_NB );

open(my $config_fh, '<', $config_qfn)
   or die("Can't open config file \"$config_qfn\": $!\n");

if (!flock($config_fh, LOCK_EX | LOCK_NB)) {
   if ($!{EWOULDBLOCK}) {
      die("Config file $config_qfn already in use\n");
   }

   die("Error trying to lock the config file: $!\n");
}

... # Rest of program. Don't close $config_fh

edited Nov 26 '13 at 20:34

answered Nov 26 '13 at 20:25

ikegami

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he wants to prevent multiple PID from using same config, so LOCK_EX seems right choice. – mpapec Nov 26 '13 at 20:32
@mpapec, Herp derp. Fixed. – ikegami Nov 26 '13 at 20:35
@mpapec, `man 2 flock`. You might also want to look at `%!` in perlvar. – ikegami Nov 26 '13 at 20:35
1

+1. ok, so everything that works regarding flock on ext3/linux is portable to win? – mpapec Nov 26 '13 at 20:44

Is there a way in Perl to tell if a Perl process in Windows is using a specific file?

1 Answers1