Memcached::cas

Description

Memcached::cas() performs a "check and set" operation, so that the item will be stored only if no other client has updated it since it was last fetched by this client. The check is done via the cas_token parameter which is a unique 64-bit value assigned to the existing item by memcache. See the documentation for Memcached::get* methods for how to obtain this token. Note that the token is represented as a float due to the limitations of PHP's integer space.

Parameters

cas_token

Unique value associated with the existing item. Generated by memcache.

key

Key

value

Value

expiration

Expiration

Return Values

Success The Memcached::getResultCode will return Memcached::RES_DATA_EXISTS if the item you are trying to store has been modified since you last fetched it.

Examples

Memcached::cas() example

<?php
$m = new Memcached();
$m->addServer('localhost', 11211);

do {
    /* fetch IP list and its token */
    $ips = $m->get('ip_block', null, $cas);
    /* if list doesn't exist yet, create it and do
       an atomic add which will fail if someone else already added it */
    if ($m->getResultCode() == Memcached::RES_NOTFOUND) {
        $ips = array($_SERVER['REMOTE_ADDR']);
        $m->add('ip_block', $ips);
    /* otherwise, add IP to the list and store via compare-and-swap
       with the token, which will fail if someone else updated the list */
    } else { 
        $ips[] = $_SERVER['REMOTE_ADDR'];
        $m->cas($cas, 'ip_block', $ips);
    }   
} while ($m->getResultCode() != Memcached::RES_SUCCESS);

?>

See Also

• Memcached::casByKey