Re: Ensure only one instance of a script is running

[Jeremiah Fisher <thisisroot@xxxxxxxxx>]

Test for a lock file when the script starts, and remove it when the 
script ends. This isn't 100% reliable, but it's the typical solution to 
this problem. If the script fails, the lock file may not be removed 
(ever have a Mozilla browser crash and tell you the default profile is 
locked?), so be careful with your error handling!

<?php

// test for lock file
if ( !$f = fopen( 'lock', 'r')) {
	// touch the lock file
	$f = fopen( 'lock', 'w');
	fwrite( $f, 'lock');
	fclose( $f);

} else {
	// lock file exists; another instance must be running (we hope)
	echo 'Error: An instance of this script is already running!';
	exit( 1);

}


/* script stuff */


// remove the lock file for the next instance
unlink( 'lock');


?>

Shaun wrote:
> Hi,
>
> 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?
>
> Many thanks 

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