Memcached::cas
(PECL memcached >= 0.1.0)
Memcached::cas — Compare and swap an item
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 double due to the
limitations of PHP's integer space.
Parameters
-
cas_token -
Unique value associated with the existing item. Generated by memcache.
-
key -
The key under which to store the value.
-
value -
The value to store.
-
expiration -
The expiration time, defaults to 0. See Expiration Times for more info.
Return Values
Returns true on success or false on failure.
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
Example #1 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);
?>
