FlockDir(3)

NAME
FlockDir - override perl flock() for network or portability purposes

SYNOPSIS
use File::FlockDir qw (open close flock);

open (FH, ">$path");

flock(FH, 2);

close FH;

DESCRIPTION
A flock module for Windows9x and other systems lacking a good perl flock() function (not platform specific)

Usage:

use File::FlockDir qw (open close flock);

OR (careful)

use File::FlockDir qw (GLOBAL_open GLOBAL_close GLOBAL_flock);

Rationale: flock on Win95/98 is badly broken but perl code needs to be portable. One way to do this is to override perl's open(), flock(), and close(). We then get an absolute file specification for all opened files and and use it in a hash to create a unique lock for the file using the File::LockDir module from Perl Cookbook, by Christiansen and Torkington (O'Reilly, 1998). This module may be included in the CPAN distribution but belongs to those authors. New code is deliberately kept at a minimum. As with nflock(), this will allow flock() to work over a network (usually).

KNOWN PROBLEMS AND LIMITATIONS

•   May be slow compared to unix flock(). This is mainly due to the fact it depends upon non-buffered disk writes (directory creation) for its implementation. May be speeded up somewhat by importing and setting the variable $Max_SH_Processes to a smaller value as long as no more than a few processes will be using shared locks at a time on any one file.

•   Abnormal termination may leave File::LockDir entries still on the drive. This means the directory locks set by File::LockDir may have to be removed after a system crash to prevent the module from assuming that files locked at the time of the crash are still locked later. This may be partially overcome by importing and setting the variable $Assume_LockDir_Zombie_Minutes to a value equal to the maximal number of minutes a lock is to be allowed to exist (defaults to one week or 10040 minutes).

•   Since the implementation creates a subdirectory in the directory containing the file that you flock(), you must have permission to create a directory where the file is located in order to flock() that file over the network.

CREDITS
Perl Cookbook, by Tom Christiansen and Nathan Torkington.

This module is an extension of Perl Cookbook's nflock(), in chapter 7, section 21 (7.21, pp 264-266).

AUTHOR
William Herrera <wherrera@lynxview.com>