Re: locking over the network

[rowdog]

If windows supports hard links you could try something like this.

#!/usr/bin/perl
use strict;
use warnings;

open my $fh, ">", "mylock.$$" or die "open mylock.$$: $!";
sleep 2 until get_lock();
print "locked> ";
<>;
unlink "mylock";    # releases the lock
unlink "mylock.$$"; # just cleaning up

sub get_lock {
    link "mylock.$$", "mylock" and return 1;
    return (stat "mylock.$$" )[3] == 2;
}

The above is based on the discussion of portably locking with link(2) as found on the Linux man page for open(2) in the O_EXCL discussion.

Edit: added comments because one unlink matters and the other doesn't.

[rovf]

If windows supports hard links ...

To be honest, I thought that the concept of hard links works only within a filesystem. I don't know how Windows does it, but with, for example, Samba, you don't have a node number where you could hard-link to, do you?

[rowdog]

To be honest, I thought that the concept of hard links works only within a filesystem.

Yes, that's my understanding as well, which is why my example does its work in the current directory.

I don't know how Windows does it, but with, for example, Samba, you don't have a node number where you could hard-link to, do you?

smbclient(1) seems to support hard links but I really can't say whether perl's link command works on a samba mount.

[tye]

Perl's link works on an SMB mount of an NTFS volume (for non-ancient versions of Perl and non-ancient Windows operating systems).

I'd be more worried about getting the link count. That is a surprisingly complex and expensive operation under NTFS, as I understand it. But simplistic testing shows that it works okay using native Win32 Perl and Cygwin Perl to a NTFS volume over SMB.