NAME File::NFSLock - perl module to do NFS (or not) locking SYNOPSIS use File::NFSLock (uncache); my $file = "somefile"; ### set up a lock - lasts until object looses scope if( defined(my $lock = File::NFSLock->new({ file => $file, lock_type => "NONBLOCKING" blocking_timeout => 10, # 10 sec stale_lock_timeout => 30 * 60, # 60 min })) ){ ### OR ### my $lock = File::NFSLock->new($file,"NONBLOCKING",10,30*60) ### do write protected stuff on $file ### at this point $file is uncached from NFS (most recent) open(FILE, "+<$file") || die $!; ### or open it any way you like ### my $fh = IO::File->open( $file, 'w' ) || die $! ### update (uncache across NFS) other files uncache("someotherfile1"); uncache("someotherfile2"); # open(FILE2,"someotherfile1"); ### unlock it $lock->unlock(); ### OR ### undef $lock; ### OR let $lock go out of scope }else{ die "I couldn't lock the file [$File::NFSLock::errstr]"; } DESCRIPTION Program based of concept of hard linking of files being atomic across NFS. This concept was mentioned in Mail::Box::Locker (which was originally presented in Mail::Folder::Maildir). Some routine flow is taken from there -- particularly the idea of creating a random local file, hard linking a common file to the local file, and then checking the nlink status. Some ideologies were not complete (uncache mechanism, shared locking) and some coding was even incorrect (wrong stat index). File::NFSLock was written to be light, generic, and fast. USAGE Locking occurs by creating a File::NFSLock object. If the object is created successfully, a lock is currently in place and remains in place until the lock object goes out of scope (or calls the unlock method). A lock object is created by calling the new method and passing two to four parameters in the following manner: my $lock = File::NFSLock->new($file, $lock_type, $blocking_timeout, $stale_lock_timeout, ); Additionally, parameters may be passed as a hashref: my $lock = File::NFSLock->new({ file => $file, lock_type => $lock_type, blocking_timeout => $blocking_timeout, stale_lock_timeout => $stale_lock_timeout, }); PARAMETERS Parameter 1: file Filename of the file upon which it is anticipated that a write will happen to. Locking will provide the most recent version (uncached) of this file upon a successful file lock. It is not necessary for this file to exist. Parameter 2: lock_type Lock type must be one of the following: BLOCKING BL EXCLUSIVE (BLOCKING) EX NONBLOCKING NB SHARED SH Fcntl::LOCK_EX() (BLOCKING) Fcntl::LOCK_NB() (NONBLOCKING) Fcntl::LOCK_SH() (SHARED) Lock type determines whether the lock will be blocking, non blocking, or shared. Blocking locks will wait until other locks are removed before the process continues. Non blocking locks will return undef if another process currently has the lock. Shared will allow other process to do a shared lock at the same time (shared is not yet implemented). Parameter 3: blocking_timeout (optional) Timeout is used in conjunction with a blocking timeout. If specified, File::NFSLock will block up to the number of seconds specified in timeout before returning undef (could not get a lock). Parameter 4: stale_lock_timeout (optional) Timeout is used to see if an existing lock file is older than the stale lock timeout. If do_lock fails to get a lock, the modified time is checked and do_lock is attempted again. If the stale_lock_timeout is set to low, a recursion load could exist so do_lock will only recurse 10 times (this is only a problem if the stale_lock_timeout is set too low -- on the order of one or two seconds). FAILURE On failure, a global variable, $File::NFSLock::errstr, should be set and should contain the cause for the failure to get a lock. Useful primarily for debugging. LOCK_EXTENSION By default File::NFSLock will use a lock file extenstion of ".NFSLock". This is now in a global variable $File::NFSLock::LOCK_EXTENSION that may be changed to suit other purposes (such as compatibility in mail systems). TODO Features yet to be implemented... SHARED locks Need to allow for shared locking. This will allow for safe reading on files. Underway. Tests Improve the test suite. AUTHORS Paul T Seamons (paul@seamons.com) - Performed majority of the programming with copious amounts of input from Rob Brown. Rob B Brown (rob@roobik.com) - In addition to helping in the programming, Rob Brown provided most of the core testing to make sure implementation worked properly. Also Mark Overmeer (mark@overmeer.net) - Author of Mail::Box::Locker, from which some key concepts for File::NFSLock were taken. Also Kevin Johnson (kjj@pobox.com) - Author of Mail::Folder::Maildir, from which Mark Overmeer based Mail::Box::Locker. COPYRIGHT Copyright (C) 2001, Paul T Seamons paul@seamons.com http://seamons.com/ Rob B Brown rob@roobik.com This package may be distributed under the terms of either the GNU General Public License or the Perl Artistic License All rights reserved.