Updated the HEAD build version to 20090527
[moodle.git] / lib / eaccelerator.class.php
CommitLineData
2142d492 1<?php
2/**
3 ** This class abstracts eaccelerator/turckmmcache
4 ** API to provide
5 **
6 ** - get()
7 ** - set()
8 ** - delete()
9 ** - getforfill()
10 ** - releaseforfill()
11 **
12 ** Author: Martin Langhoff <martin@catalyst.net.nz>
13 **
f917d0ea 14 ** Note: do NOT store booleans here. For compatibility with
15 ** memcached, a false value is indistinguisable from a
16 ** "not found in cache" response.
2142d492 17 **/
18
19
20class eaccelerator {
21
22 function eaccelerator() {
23 global $CFG;
24 if ( function_exists('eaccelerator_get')) {
85cab9d8 25 $this->mode = 'eaccelerator';
2142d492 26 } elseif (function_exists('mmcache_get')) {
85cab9d8 27 $this->mode = 'mmcache';
2142d492 28 } else {
29 debugging("\$CFG->eaccelerator is set to true but the required functions are not available. You need to have either eaccelerator or turckmmcache extensions installed, compiled with the shmem keys option enabled.");
30 }
31
2142d492 32 $this->prefix = $CFG->dbname .'|' . $CFG->prefix . '|';
33 }
34
35 function status() {
36 if (isset($this->mode)) {
37 return true;
38 }
39 return false;
40 }
41
42 function set($key, $value, $ttl=0) {
43 $set = $this->mode . '_put';
44 $unlock = $this->mode . '_unlock';
45
46 // we may have acquired a lock via getforfill
47 // release if it exists
48 @$unlock($this->prefix . $key . '_forfill');
49
50 return $set($this->prefix . $key, serialize($value), $ttl);
51 }
52
53 function get($key) {
54 $fn = $this->mode . '_get';
55 $rec = $fn($this->prefix . $key);
56 if (is_null($rec)) {
f917d0ea 57 return false;
2142d492 58 }
59 return unserialize($rec);
60 }
61
62 function delete($key) {
63 $fn = $this->mode . '_rm';
64 return $fn($this->prefix . $key);
65 }
66
67 /**
68 * In the simple case, this function will
69 * get the cached value if available. If the entry
70 * is not cached, it will try to get an exclusive
71 * lock that announces that this process will
72 * populate the cache.
73 *
74 * If we fail to get the lock -- this means another
75 * process is doing it.
76 * so we wait (block) for a few microseconds while we wait for
77 * the cache to be filled or the lock to timeout.
78 *
79 * If you get a false from this call, you _must_
80 * populate the cache ASAP or indicate that
81 * you won't by calling releaseforfill().
82 *
83 * This technique forces serialisation and so helps deal
84 * with thundering herd scenarios where a lot of clients
85 * ask the for the same idempotent (and costly) operation.
86 * The implementation is based on suggestions in this message
87 * http://marc.theaimsgroup.com/?l=git&m=116562052506776&w=2
88 *
89 * @param $key string
f917d0ea 90 * @return mixed on cache hit, false otherwise
2142d492 91 */
92 function getforfill ($key) {
93 $get = $this->mode . '_get';
94 $lock = $this->mode . '_lock';
95
96 $rec = $get($this->prefix . $key);
97 if (!is_null($rec)) {
98 return unserialize($rec);
99 }
100 if ($lock($this->prefix . $key . '_forfill')) {
101 // we obtained the _forfill lock
102 // our caller will compute and set the value
f917d0ea 103 return false;
2142d492 104 }
105 // someone else has the lock
106 // "block" till we can get the value
107 // actually, loop .05s waiting for it
108 for ($n=0;$n<5;$n++) {
109 usleep(10000);
110 $rec = $get($this->prefix . $key);
111 if (!is_null($rec)) {
112 return unserialize($rec);
113 }
114 }
f917d0ea 115 return false;
2142d492 116 }
117
118 /**
119 * Release the exclusive lock obtained by
120 * getforfill(). See getforfill()
121 * for more details.
122 *
123 * @param $key string
124 * @return bool
125 */
126 function releaseforfill ($key) {
127 $unlock = $this->mode . '_unlock';
128 return $unlock($this->prefix . $key . '_forfill');
129 }
130}
131
132?>