Re: [mv] Flock Locking over NFS

[Mike Heins <mikeh@minivend.com>]

******    message to minivend-users from Mike Heins <mikeh@minivend.com>     ******

Quoting Kevin Walsh (kevin@cursor-software.co.uk):
> 
> MiniVend currently uses flock to lock its files but flock is not
> supported on Linux when locking files over NFS.

Hmm. My understanding is that Perl uses fcntl when locking NFS file
systems; I have done some fairly heavy lock testing on NFS-mounted
systems to verify this.

> 
> The following patch adds a fcntl locking mechanism that is
> supported on Linux/NFS.  Perhaps someone other than us will find
> it useful when setting up a MiniVend farm with a shared session
> database.

I will look into this; as well as a mechanism for selecting it. I am
not sure it can be done on a catalog-by-catalog basis, but it certainly
could be selected in minivend.cfg.

Thanks for the contribution!

> 
> The patch is for lib/Vend/Util.pm (MV 4.04).
> 
> -------------------CUT HERE-----------------------------
> 908a909,944
> > ### fcntl locking
> > 
> > sub fcntl_lock {
> >     my ($fh, $excl, $wait) = @_;
> >     my $flag = $excl ? F_WRLCK : F_RDLCK;
> >     my $buf = pack("ssLL",$flag,0,0,0);
> > 
> >     LOCKLOOP:{
> >         if ($wait) {
> >             if (! fcntl($fh, F_SETLKW, $buf)) {
> >                 redo LOCKLOOP if $! =~ m/^Interrupted/;
> >                 die "Could not lock file: $!\n";
> >             }
> >         }
> >         else {
> >             if (! fcntl($fh, F_SETLK, $buf)) {
> >                 redo LOCKLOOP if $! =~ m/^Interrupted/;
> >                 if ($! =~ m/^Try again/
> >                     or $! =~ m/^Resource temporarily unavailable/
> >                     or $! =~ m/^Operation would block/) {
> >                     return 0;
> >                 }
> >                 die "Could not lock file: $!\n";
> >             }
> >         }
> >         return 1;
> >     }
> > }
> > 
> > sub fcntl_unlock {
> >     my ($fh) = @_;
> >     my $buf = pack("ssLL",F_WRLCK,0,0,0);
> >     fcntl($fh, F_UNLCK, $buf) or die "Could not unlock file: $!\n";
> > }
> > 
> > 
> 917c953
> <         $use = 'flock';
> ---
> >         $use = 'fcntl';
> 926a963,966
> > }
> > elsif ($use eq 'fcntl') {
> >     $lock_function = \&fcntl_lock;
> >     $unlock_function = \&fcntl_unlock;
> -------------------CUT HERE-----------------------------
> 

-- 
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phone +1.513.523.7621 fax 7501 <heins@akopia.com>

Research is what I'm doing when I don't know what I'm doing.
-- Wernher Von Braun
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