I read all the stuff about flock and its traps,and the biggest one is always at the end, where it always sounds like "Some versions of flock() can't lock files over a network (e.g. on NFS file systems)" etc. I need to lock files over NFS, so I read the stuff about fcntl, but it looked rather complicated. I found a different solution in the manpage open(2) in the section about O_EXCL. It goes like this: 
sub lock {
  my $lockhelper="lockhelper-$ENV{HOSTNAME}-$$.LCK";
  my *LOCK;
  my $nlink;

  open(LOCK, ">$lockhelper") or die "Couldn't open() $lockhelper: $!";
+ 
  print LOCK "$ENV{HOSTNAME};$$\n";                       
  close(LOCK);
  link($lockhelper, "lockfile.LCK");
  (undef,undef,undef,$nlink,undef,undef,undef,undef,
   undef,undef,undef,undef,undef) = stat($lockhelper);
  unlink($lockhelper);
  return $nlink==2;
}

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If this sub returns true, you have got the lock, it is nonblocking. My Question is: Is this really the way to do it if you have to deal with NFS, or is there a more elegant way ?
- chb

In reply to File locking on NFS by chb

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