<?php
/*
* Copyright 2010 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* A persistent storage class based on the APC cache, which is not
* really very persistent, as soon as you restart your web server
* the storage will be wiped, however for debugging and/or speed
* it can be useful, kinda, and cache is a lot cheaper then storage.
*
* @author Chris Chabot <chabotc@google.com>
*/
class googleApcCache extends Google_Cache {
public function __construct() {
if (! function_exists('apc_add')) {
throw new Google_CacheException("Apc functions not available");
}
}
private function isLocked($key) {
if ((@apc_fetch($key . '.lock')) === false) {
return false;
}
return true;
}
private function createLock($key) {
// the interesting thing is that this could fail if the lock was created in the meantime..
// but we'll ignore that out of convenience
@apc_add($key . '.lock', '', 5);
}
private function removeLock($key) {
// suppress all warnings, if some other process removed it that's ok too
@apc_delete($key . '.lock');
}
private function waitForLock($key) {
// 20 x 250 = 5 seconds
$tries = 20;
$cnt = 0;
do {
// 250 ms is a long time to sleep, but it does stop the server from burning all resources on polling locks..
usleep(250);
$cnt ++;
} while ($cnt <= $tries && $this->isLocked($key));
if ($this->isLocked($key)) {
// 5 seconds passed, assume the owning process died off and remove it
$this->removeLock($key);
}
}
/**
* @inheritDoc
*/
public function get($key, $expiration = false) {
if (($ret = @apc_fetch($key)) === false) {
return false;
}
if (!$expiration || (time() - $ret['time'] > $expiration)) {
$this->delete($key);
return false;
}
return unserialize($ret['data']);
}
/**
* @inheritDoc
*/
public function set($key, $value) {
if (@apc_store($key, array('time' => time(), 'data' => serialize($value))) == false) {
throw new Google_CacheException("Couldn't store data");
}
}
/**
* @inheritDoc
* @param String $key
*/
public function delete($key) {
@apc_delete($key);
}
}
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