Posted by Robert Cummings on 03/16/05 20:07

On Wed, 2005-03-16 at 11:12, Jay Blanchard wrote:
> [snip]
> I have a script that inserts data from files uploaded to our server. I
> need
> to make sure that only one instance of this script runs at anyone time,
> can
> anyone tell me how I can do this?
> [/snip]
>
> Don't run another instance. ba-dump ching!
>
> Ok, here is a quick and dirty way to do it, have the script check for
> the existence of a file containing a date and timestamp, if one does not
> exist the script creates one. If it does exist, the script exits. Once
> the script is nearing completion have it destroy the file (unlink).

Here's a simple script which uses directories for locking which is
superior to the above example that doesn't cater to race conditions. It
uses directory creation since directory creation is supposedly atomic on
a non NFS filesystem.

<?
function lockCreate( $name )
{
$myPath = ereg_replace( '/[^/]+$', '/', __FILE__ );
$lockPath = $myPath.$name.'.lock';
$status = @mkdir( $lockPath );

return $status;
}

function lockDestroy( $name )
{
$myPath = ereg_replace( '/[^/]+$', '/', __FILE__ );
$lockPath = $myPath.$name.'.lock';

$status = @rmdir( $lockPath );

return $status;
}

if( !lockCreate( $lockName ) )
{
//
// Script already running.
//
exit();
}

//
// Do stuff here then afterwards remove the lock.
//

lockDestroy( $lockName );
?>

HTH and HAND,
Rob.
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