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<?php
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/*
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* Copyright 2008 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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* A persistent storage class based on the memcache, which is not
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* really very persistent, as soon as you restart your memcache daemon
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* the storage will be wiped, however for debugging and/or speed
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* it can be useful, kinda, and cache is a lot cheaper then storage.
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*
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* @author Chris Chabot <chabotc@google.com>
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*/
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class Google_MemcacheCache extends Google_Cache {
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private $connection = false;
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public function __construct() {
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global $apiConfig;
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if (! function_exists('memcache_connect')) {
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throw new Google_CacheException("Memcache functions not available");
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}
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$this->host = $apiConfig['ioMemCacheCache_host'];
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$this->port = $apiConfig['ioMemCacheCache_port'];
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if (empty($this->host) || empty($this->port)) {
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throw new Google_CacheException("You need to supply a valid memcache host and port");
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}
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}
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private function isLocked($key) {
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$this->check();
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if ((@memcache_get($this->connection, $key . '.lock')) === false) {
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return false;
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}
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return true;
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}
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private function createLock($key) {
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$this->check();
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// the interesting thing is that this could fail if the lock was created in the meantime..
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// but we'll ignore that out of convenience
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@memcache_add($this->connection, $key . '.lock', '', 0, 5);
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}
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private function removeLock($key) {
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$this->check();
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// suppress all warnings, if some other process removed it that's ok too
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@memcache_delete($this->connection, $key . '.lock');
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}
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private function waitForLock($key) {
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$this->check();
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// 20 x 250 = 5 seconds
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$tries = 20;
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$cnt = 0;
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do {
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// 250 ms is a long time to sleep, but it does stop the server from burning all resources on polling locks..
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usleep(250);
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$cnt ++;
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} while ($cnt <= $tries && $this->isLocked($key));
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if ($this->isLocked($key)) {
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// 5 seconds passed, assume the owning process died off and remove it
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$this->removeLock($key);
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}
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}
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// I prefer lazy initialization since the cache isn't used every request
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// so this potentially saves a lot of overhead
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private function connect() {
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if (! $this->connection = @memcache_pconnect($this->host, $this->port)) {
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throw new Google_CacheException("Couldn't connect to memcache server");
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}
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}
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private function check() {
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if (! $this->connection) {
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$this->connect();
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}
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}
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/**
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* @inheritDoc
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*/
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public function get($key, $expiration = false) {
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$this->check();
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if (($ret = @memcache_get($this->connection, $key)) === false) {
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return false;
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}
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if (! $expiration || (time() - $ret['time'] > $expiration)) {
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$this->delete($key);
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return false;
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}
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return $ret['data'];
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}
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/**
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* @inheritDoc
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* @param string $key
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* @param string $value
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* @throws Google_CacheException
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*/
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public function set($key, $value) {
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$this->check();
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// we store it with the cache_time default expiration so objects will at least get cleaned eventually.
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if (@memcache_set($this->connection, $key, array('time' => time(),
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'data' => $value), false) == false) {
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throw new Google_CacheException("Couldn't store data in cache");
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}
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}
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/**
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* @inheritDoc
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* @param String $key
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*/
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public function delete($key) {
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$this->check();
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@memcache_delete($this->connection, $key);
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}
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}
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