Memcached::cas

Compare and swap an item

&reftitle.description; public `bool` `Memcached::cas` ``string``int``float```cas_token` `string` `key` `mixed` `value` `int` `expiration` 0

`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.

&reftitle.parameters;

`cas_token`

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

`key`

- &memcached.parameter.key;

`value`

- &memcached.parameter.value;

`expiration`

- &memcached.parameter.expiration;

&reftitle.returnvalues;

&return.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.

&reftitle.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);

    ?>

&reftitle.seealso;

- `Memcached::casByKey`