lib/google/cache/Google_ApcCache.php

   1 <?php
   2 /*
   3  * Copyright 2010 Google Inc.
   4  *
   5  * Licensed under the Apache License, Version 2.0 (the "License");
   6  * you may not use this file except in compliance with the License.
   7  * You may obtain a copy of the License at
   8  *
   9  *     http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing, software
  12  * distributed under the License is distributed on an "AS IS" BASIS,
  13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14  * See the License for the specific language governing permissions and
  15  * limitations under the License.
  16  */
  17
  18 /**
  19  * A persistent storage class based on the APC cache, which is not
  20  * really very persistent, as soon as you restart your web server
  21  * the storage will be wiped, however for debugging and/or speed
  22  * it can be useful, kinda, and cache is a lot cheaper then storage.
  23  *
  24  * @author Chris Chabot <chabotc@google.com>
  25  */
  26 class googleApcCache extends Google_Cache {
  27
  28   public function __construct() {
  29     if (! function_exists('apc_add')) {
  30       throw new Google_CacheException("Apc functions not available");
  31     }
  32   }
  33
  34   private function isLocked($key) {
  35     if ((@apc_fetch($key . '.lock')) === false) {
  36       return false;
  37     }
  38     return true;
  39   }
  40
  41   private function createLock($key) {
  42     // the interesting thing is that this could fail if the lock was created in the meantime..
  43     // but we'll ignore that out of convenience
  44     @apc_add($key . '.lock', '', 5);
  45   }
  46
  47   private function removeLock($key) {
  48     // suppress all warnings, if some other process removed it that's ok too
  49     @apc_delete($key . '.lock');
  50   }
  51
  52   private function waitForLock($key) {
  53     // 20 x 250 = 5 seconds
  54     $tries = 20;
  55     $cnt = 0;
  56     do {
  57       // 250 ms is a long time to sleep, but it does stop the server from burning all resources on polling locks..
  58       usleep(250);
  59       $cnt ++;
  60     } while ($cnt <= $tries && $this->isLocked($key));
  61     if ($this->isLocked($key)) {
  62       // 5 seconds passed, assume the owning process died off and remove it
  63       $this->removeLock($key);
  64     }
  65   }
  66
  67    /**
  68    * @inheritDoc
  69    */
  70   public function get($key, $expiration = false) {
  71
  72     if (($ret = @apc_fetch($key)) === false) {
  73       return false;
  74     }
  75     if (!$expiration || (time() - $ret['time'] > $expiration)) {
  76       $this->delete($key);
  77       return false;
  78     }
  79     return unserialize($ret['data']);
  80   }
  81
  82   /**
  83    * @inheritDoc
  84    */
  85   public function set($key, $value) {
  86     if (@apc_store($key, array('time' => time(), 'data' => serialize($value))) == false) {
  87       throw new Google_CacheException("Couldn't store data");
  88     }
  89   }
  90
  91   /**
  92    * @inheritDoc
  93    * @param String $key
  94    */
  95   public function delete($key) {
  96     @apc_delete($key);
  97   }
  98 }