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 */
26class 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}
99