This file is indexed.

/usr/share/perl5/File/NFSLock.pm is in libfile-nfslock-perl 1.21-1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
# -*- perl -*-
#
#  File::NFSLock - bdpO - NFS compatible (safe) locking utility
#
#  $Id: NFSLock.pm,v 1.34 2003/05/13 18:06:41 hookbot Exp $
#
#  Copyright (C) 2002, Paul T Seamons
#                      paul@seamons.com
#                      http://seamons.com/
#
#                      Rob B Brown
#                      bbb@cpan.org
#
#  This package may be distributed under the terms of either the
#  GNU General Public License
#    or the
#  Perl Artistic License
#
#  All rights reserved.
#
#  Please read the perldoc File::NFSLock
#
################################################################

package File::NFSLock;

use strict;
use warnings;

use Carp qw(croak confess);
our $errstr;
use base 'Exporter';
our @EXPORT_OK = qw(uncache);

our $VERSION = '1.21';

#Get constants, but without the bloat of
#use Fcntl qw(LOCK_SH LOCK_EX LOCK_NB);
use constant {
   LOCK_SH => 1,
   LOCK_EX => 2,
   LOCK_NB => 4,
};

### Convert lock_type to a number
our $TYPES = {
  BLOCKING    => LOCK_EX,
  BL          => LOCK_EX,
  EXCLUSIVE   => LOCK_EX,
  EX          => LOCK_EX,
  NONBLOCKING => LOCK_EX | LOCK_NB,
  NB          => LOCK_EX | LOCK_NB,
  SHARED      => LOCK_SH,
  SH          => LOCK_SH,
};
our $LOCK_EXTENSION = '.NFSLock'; # customizable extension
our $HOSTNAME = undef;
our $SHARE_BIT = 1;

###----------------------------------------------------------------###

my $graceful_sig = sub {
  print STDERR "Received SIG$_[0]\n" if @_;
  # Perl's exit should safely DESTROY any objects
  # still "alive" before calling the real _exit().
  exit;
};

our @CATCH_SIGS = qw(TERM INT);

sub new {
  $errstr = undef;

  my $type  = shift;
  my $class = ref($type) || $type || __PACKAGE__;
  my $self  = {};

  ### allow for arguments by hash ref or serially
  if( @_ && ref $_[0] ){
    $self = shift;
  }else{
    $self->{file}      = shift;
    $self->{lock_type} = shift;
    $self->{blocking_timeout}   = shift;
    $self->{stale_lock_timeout} = shift;
  }
  $self->{file}       ||= "";
  $self->{lock_type}  ||= 0;
  $self->{blocking_timeout}   ||= 0;
  $self->{stale_lock_timeout} ||= 0;
  $self->{lock_pid} = $$;
  $self->{unlocked} = 1;
  foreach my $signal (@CATCH_SIGS) {
    if (!$SIG{$signal} ||
        $SIG{$signal} eq "DEFAULT") {
      $SIG{$signal} = $graceful_sig;
    }
  }

  ### force lock_type to be numerical
  if( $self->{lock_type} &&
      $self->{lock_type} !~ /^\d+/ &&
      exists $TYPES->{$self->{lock_type}} ){
    $self->{lock_type} = $TYPES->{$self->{lock_type}};
  }

  ### need the hostname
  if( !$HOSTNAME ){
    require Sys::Hostname;
    $HOSTNAME = Sys::Hostname::hostname();
  }

  ### quick usage check
  croak ($errstr = "Usage: my \$f = $class->new('/pathtofile/file',\n"
         ."'BLOCKING|EXCLUSIVE|NONBLOCKING|SHARED', [blocking_timeout, stale_lock_timeout]);\n"
         ."(You passed \"$self->{file}\" and \"$self->{lock_type}\")")
    unless length($self->{file});

  croak ($errstr = "Unrecognized lock_type operation setting [$self->{lock_type}]")
    unless $self->{lock_type} && $self->{lock_type} =~ /^\d+$/;

  ### Input syntax checking passed, ready to bless
  bless $self, $class;

  ### choose a random filename
  $self->{rand_file} = rand_file( $self->{file} );

  ### choose the lock filename
  $self->{lock_file} = $self->{file} . $LOCK_EXTENSION;

  my $quit_time = $self->{blocking_timeout} &&
    !($self->{lock_type} & LOCK_NB) ?
      time() + $self->{blocking_timeout} : 0;

  ### remove an old lockfile if it is older than the stale_timeout
  if( -e $self->{lock_file} &&
      $self->{stale_lock_timeout} > 0 &&
      time() - (stat _)[9] > $self->{stale_lock_timeout} ){
    unlink $self->{lock_file};
  }

  while (1) {
    ### open the temporary file
    $self->create_magic
      or return undef;

    if ( $self->{lock_type} & LOCK_EX ) {
      last if $self->do_lock;
    } elsif ( $self->{lock_type} & LOCK_SH ) {
      last if $self->do_lock_shared;
    } else {
      $errstr = "Unknown lock_type [$self->{lock_type}]";
      return undef;
    }

    ### Lock failed!

    ### I know this may be a race condition, but it's okay.  It is just a
    ### stab in the dark to possibly find long dead processes.

    ### If lock exists and is readable, see who is mooching on the lock

    my $fh;
    if ( -e $self->{lock_file} &&
         open ($fh,'+<', $self->{lock_file}) ){

      my @mine = ();
      my @them = ();
      my @dead = ();

      my $has_lock_exclusive = !((stat _)[2] & $SHARE_BIT);
      my $try_lock_exclusive = !($self->{lock_type} & LOCK_SH);

      while(defined(my $line=<$fh>)){
        if ($line =~ /^$HOSTNAME (-?\d+) /) {
          my $pid = $1;
          if ($pid == $$) {       # This is me.
            push @mine, $line;
          }elsif(kill 0, $pid) {  # Still running on this host.
            push @them, $line;
          }else{                  # Finished running on this host.
            push @dead, $line;
          }
        } else {                  # Running on another host, so
          push @them, $line;      #  assume it is still running.
        }
      }

      ### If there was at least one stale lock discovered...
      if (@dead) {
        # Lock lock_file to avoid a race condition.
        local $LOCK_EXTENSION = ".shared";
        my $lock = new File::NFSLock {
          file => $self->{lock_file},
          lock_type => LOCK_EX,
          blocking_timeout => 62,
          stale_lock_timeout => 60,
        };

        ### Rescan in case lock contents were modified between time stale lock
        ###  was discovered and lockfile lock was acquired.
        seek ($fh, 0, 0);
        my $content = '';
        while(defined(my $line=<$fh>)){
          if ($line =~ /^$HOSTNAME (-?\d+) /) {
            my $pid = $1;
            next if (!kill 0, $pid);  # Skip dead locks from this host
          }
          $content .= $line;          # Save valid locks
        }

        ### Save any valid locks or wipe file.
        if( length($content) ){
          seek     $fh, 0, 0;
          print    $fh $content;
          truncate $fh, length($content);
          close    $fh;
        }else{
          close $fh;
          unlink $self->{lock_file};
        }

      ### No "dead" or stale locks found.
      } else {
        close $fh;
      }

      ### If attempting to acquire the same type of lock
      ###  that it is already locked with, and I've already
      ###  locked it myself, then it is safe to lock again.
      ### Just kick out successfully without really locking.
      ### Assumes locks will be released in the reverse
      ###  order from how they were established.
      if ($try_lock_exclusive eq $has_lock_exclusive && @mine){
        return $self;
      }
    }

    ### If non-blocking, then kick out now.
    ### ($errstr might already be set to the reason.)
    if ($self->{lock_type} & LOCK_NB) {
      $errstr ||= "NONBLOCKING lock failed!";
      return undef;
    }

    ### wait a moment
    sleep(1);

    ### but don't wait past the time out
    if( $quit_time && (time > $quit_time) ){
      $errstr = "Timed out waiting for blocking lock";
      return undef;
    }

    # BLOCKING Lock, So Keep Trying
  }

  ### clear up the NFS cache
  $self->uncache;

  ### Yes, the lock has been aquired.
  delete $self->{unlocked};

  return $self;
}

sub DESTROY {
  shift()->unlock();
}

sub unlock ($) {
  my $self = shift;
  if (!$self->{unlocked}) {
    unlink( $self->{rand_file} ) if -e $self->{rand_file};
    if( $self->{lock_type} & LOCK_SH ){
      return $self->do_unlock_shared;
    }else{
      return $self->do_unlock;
    }
    $self->{unlocked} = 1;
    foreach my $signal (@CATCH_SIGS) {
      if ($SIG{$signal} &&
          ($SIG{$signal} eq $graceful_sig)) {
        # Revert handler back to how it used to be.
        # Unfortunately, this will restore the
        # handler back even if there are other
        # locks still in tact, but for most cases,
        # it will still be an improvement.
        delete $SIG{$signal};
      }
    }
  }
  return 1;
}

###----------------------------------------------------------------###

# concepts for these routines were taken from Mail::Box which
# took the concepts from Mail::Folder


sub rand_file ($) {
  my $file = shift;
  "$file.tmp.". time()%10000 .'.'. $$ .'.'. int(rand()*10000);
}

sub create_magic ($;$) {
  $errstr = undef;
  my $self = shift;
  my $append_file = shift || $self->{rand_file};
  $self->{lock_line} ||= "$HOSTNAME $self->{lock_pid} ".time()." ".int(rand()*10000)."\n";
  open (my $fh,'>>', $append_file) or do { $errstr = "Couldn't open \"$append_file\" [$!]"; return undef; };
  print $fh $self->{lock_line};
  close $fh;
  return 1;
}

sub do_lock {
  $errstr = undef;
  my $self = shift;
  my $lock_file = $self->{lock_file};
  my $rand_file = $self->{rand_file};
  my $chmod = 0600;
  chmod( $chmod, $rand_file)
    || die "I need ability to chmod files to adequatetly perform locking";

  ### try a hard link, if it worked
  ### two files are pointing to $rand_file
  my $success = link( $rand_file, $lock_file )
    && -e $rand_file && (stat _)[3] == 2;
  unlink $rand_file;

  return $success;
}

sub do_lock_shared {
  $errstr = undef;
  my $self = shift;
  my $lock_file  = $self->{lock_file};
  my $rand_file  = $self->{rand_file};

  ### chmod local file to make sure we know before
  my $chmod = 0600;
  $chmod |= $SHARE_BIT;
  chmod( $chmod, $rand_file)
    || die "I need ability to chmod files to adequatetly perform locking";

  ### lock the locking process
  local $LOCK_EXTENSION = ".shared";
  my $lock = new File::NFSLock {
    file => $lock_file,
    lock_type => LOCK_EX,
    blocking_timeout => 62,
    stale_lock_timeout => 60,
  };
  # The ".shared" lock will be released as this status
  # is returned, whether or not the status is successful.

  ### If I didn't have exclusive and the shared bit is not
  ### set, I have failed

  ### Try to create $lock_file from the special
  ### file with the magic $SHARE_BIT set.
  my $success = link( $rand_file, $lock_file);
  unlink $rand_file;
  if ( !$success &&
       -e $lock_file &&
       ((stat _)[2] & $SHARE_BIT) != $SHARE_BIT ){

    $errstr = 'Exclusive lock exists.';
    return undef;

  } elsif ( !$success ) {
    ### Shared lock exists, append my lock
    $self->create_magic ($self->{lock_file});
  }

  # Success
  return 1;
}

sub do_unlock ($) {
  return unlink shift->{lock_file};
}

sub do_unlock_shared ($) {
  $errstr = undef;
  my $self = shift;
  my $lock_file = $self->{lock_file};
  my $lock_line = $self->{lock_line};

  ### lock the locking process
  local $LOCK_EXTENSION = '.shared';
  my $lock = new File::NFSLock ($lock_file,LOCK_EX,62,60);

  ### get the handle on the lock file
  my $fh;
  if( ! open ($fh,'+<', $lock_file) ){
    if( ! -e $lock_file ){
      return 1;
    }else{
      die "Could not open for writing shared lock file $lock_file ($!)";
    }
  }

  ### read existing file
  my $content = '';
  while(defined(my $line=<$fh>)){
    next if $line eq $lock_line;
    $content .= $line;
  }

  ### other shared locks exist
  if( length($content) ){
    seek     $fh, 0, 0;
    print    $fh $content;
    truncate $fh, length($content);
    close    $fh;

  ### only I exist
  }else{
    close $fh;
    unlink $lock_file;
  }

}

sub uncache ($;$) {
  # allow as method call
  my $file = pop;
  ref $file && ($file = $file->{file});
  my $rand_file = rand_file( $file );

  ### hard link to the actual file which will bring it up to date
  return ( link( $file, $rand_file) && unlink($rand_file) );
}

sub newpid {
  my $self = shift;
  # Detect if this is the parent or the child
  if ($self->{lock_pid} == $$) {
    # This is the parent

    # Must wait for child to call newpid before processing.
    # A little patience for the child to call newpid
    my $patience = time + 10;
    while (time < $patience) {
      if (rename("$self->{lock_file}.fork",$self->{rand_file})) {
        # Child finished its newpid call.
        # Wipe the signal file.
        unlink $self->{rand_file};
        last;
      }
      # Brief pause before checking again
      # to avoid intensive IO across NFS.
      select(undef,undef,undef,0.1);
    }

    # Fake the parent into thinking it is already
    # unlocked because the child will take care of it.
    $self->{unlocked} = 1;
  } else {
    # This is the new child

    # The lock_line found in the lock_file contents
    # must be modified to reflect the new pid.

    # Fix lock_pid to the new pid.
    $self->{lock_pid} = $$;
    # Backup the old lock_line.
    my $old_line = $self->{lock_line};
    # Clear lock_line to create a fresh one.
    delete $self->{lock_line};
    # Append a new lock_line to the lock_file.
    $self->create_magic($self->{lock_file});
    # Remove the old lock_line from lock_file.
    local $self->{lock_line} = $old_line;
    $self->do_unlock_shared;
    # Create signal file to notify parent that
    # the lock_line entry has been delegated.
    open (my $fh, '>', "$self->{lock_file}.fork");
    close($fh);
  }
}

1;


=head1 NAME

File::NFSLock - perl module to do NFS (or not) locking

=head1 SYNOPSIS

  use File::NFSLock qw(uncache);
  use Fcntl qw(LOCK_EX LOCK_NB);

  my $file = "somefile";

  ### set up a lock - lasts until object looses scope
  if (my $lock = new File::NFSLock {
    file      => $file,
    lock_type => LOCK_EX|LOCK_NB,
    blocking_timeout   => 10,      # 10 sec
    stale_lock_timeout => 30 * 60, # 30 min
  }) {

    ### OR
    ### my $lock = File::NFSLock->new($file,LOCK_EX|LOCK_NB,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]";
  }


=head1 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.


=head1 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,
  });

=head1 PARAMETERS

=over 4

=item 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.

=item Parameter 2: lock_type

Lock type must be one of the following:

  BLOCKING
  BL
  EXCLUSIVE (BLOCKING)
  EX
  NONBLOCKING
  NB
  SHARED
  SH

Or else one or more of the following joined with '|':

  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 as long as there is not
already an exclusive lock obtained.

=item 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).


=item 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).

=back

=head1 METHODS

After the $lock object is instantiated with new,
as outlined above, some methods may be used for
additional functionality.

=head2 unlock

  $lock->unlock;

This method may be used to explicitly release a lock
that is aquired.  In most cases, it is not necessary
to call unlock directly since it will implicitly be
called when the object leaves whatever scope it is in.

=head2 uncache

  $lock->uncache;
  $lock->uncache("otherfile1");
  uncache("otherfile2");

This method is used to freshen up the contents of a
file across NFS, ignoring what is contained in the
NFS client cache.  It is always called from within
the new constructor on the file that the lock is
being attempted.  uncache may be used as either an
object method or as a stand alone subroutine.

=head2 newpid

  my $pid = fork;
  if (defined $pid) {
    # Fork Failed
  } elsif ($pid) {
    $lock->newpid; # Parent
  } else {
    $lock->newpid; # Child
  }

If fork() is called after a lock has been aquired,
then when the lock object leaves scope in either
the parent or child, it will be released.  This
behavior may be inappropriate for your application.
To delegate ownership of the lock from the parent
to the child, both the parent and child process
must call the newpid() method after a successful
fork() call.  This will prevent the parent from
releasing the lock when unlock is called or when
the lock object leaves scope.  This is also
useful to allow the parent to fail on subsequent
lock attempts if the child lock is still aquired.

=head1 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.

=head1 LOCK_EXTENSION

By default File::NFSLock will use a lock file extenstion of ".NFSLock".  This is
in a global variable $File::NFSLock::LOCK_EXTENSION that may be changed to
suit other purposes (such as compatibility in mail systems).

=head1 BUGS

Notify paul@seamons.com or bbb@cpan.org if you spot anything.

=head2 FIFO

Locks are not necessarily obtained on a first come first serve basis.
Not only does this not seem fair to new processes trying to obtain a lock,
but it may cause a process starvation condition on heavily locked files.


=head2 DIRECTORIES

Locks cannot be obtained on directory nodes, nor can a directory node be
uncached with the uncache routine because hard links do not work with
directory nodes.  Some other algorithm might be used to uncache a
directory, but I am unaware of the best way to do it.  The biggest use I
can see would be to avoid NFS cache of directory modified and last accessed
timestamps.

=head1 INSTALL

Download and extract tarball before running
these commands in its base directory:

  perl Makefile.PL
  make
  make test
  make install

For RPM installation, download tarball before
running these commands in your _topdir:

  rpm -ta SOURCES/File-NFSLock-*.tar.gz
  rpm -ih RPMS/noarch/perl-File-NFSLock-*.rpm

=head1 AUTHORS

Paul T Seamons (paul@seamons.com) - Performed majority of the
programming with copious amounts of input from Rob Brown.

Rob B Brown (bbb@cpan.org) - In addition to helping in the
programming, Rob Brown provided most of the core testing to make sure
implementation worked properly.  He is now the current maintainer.

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.

=head1 COPYRIGHT

  Copyright (C) 2001
  Paul T Seamons
  paul@seamons.com
  http://seamons.com/

  Copyright (C) 2002-2003,
  Rob B Brown
  bbb@cpan.org

  This package may be distributed under the terms of either the
  GNU General Public License
    or the
  Perl Artistic License

  All rights reserved.

=cut