MatthiasMullie\Scrapbook\Adapters\Apc::cas PHP Method

    public function cas($token, $key, $value, $expire = 0)
    {
        $ttl = $this->ttl($expire);
        // lock required because we can't perform an atomic CAS
        if (!$this->lock($key)) {
            return false;
        }
        // check for values that were just stored in this request but have
        // actually expired by now
        if (isset($this->expires[$key]) && $this->expires[$key] < time()) {
            return false;
        }
        // get current value, to compare with token
        $compare = $this->apcu_fetch($key);
        if ($compare === false) {
            $this->unlock($key);
            return false;
        }
        if ($token !== serialize($compare)) {
            $this->unlock($key);
            return false;
        }
        // negative TTLs don't always seem to properly treat the key as deleted
        if ($ttl < 0) {
            $this->apcu_delete($key);
            unset($this->expires[$key]);
            $this->unlock($key);
            return true;
        }
        $success = $this->apcu_store($key, $value, $ttl);
        $this->expire($key, $ttl);
        $this->unlock($key);
        return $success;
    }