lib/eaccelerator.class.php

   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  **
  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.
  17  **/
  18
  19
  20 class eaccelerator {
  21
  22     function eaccelerator() {
  23         global $CFG;
  24         if ( function_exists('eaccelerator_get')) {
  25             $mode = 'eaccelerator';
  26         } elseif (function_exists('mmcache_get')) {
  27             $mode = 'mmcache';
  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
  32         $this->mode   = $mode;
  33         $this->prefix = $CFG->dbname .'|' . $CFG->prefix . '|';
  34     }
  35
  36     function status() {
  37         if (isset($this->mode)) {
  38             return true;
  39         }
  40         return false;
  41     }
  42
  43     function set($key, $value, $ttl=0) {
  44         $set    = $this->mode . '_put';
  45         $unlock = $this->mode . '_unlock';
  46
  47         // we may have acquired a lock via getforfill
  48         // release if it exists
  49         @$unlock($this->prefix . $key . '_forfill');
  50
  51         return $set($this->prefix . $key, serialize($value), $ttl);
  52     }
  53
  54     function get($key) {
  55         $fn = $this->mode . '_get';
  56         $rec = $fn($this->prefix . $key);
  57         if (is_null($rec)) {
  58             return false;
  59         }
  60         return unserialize($rec);
  61     }
  62
  63     function delete($key) {
  64         $fn = $this->mode . '_rm';
  65         return $fn($this->prefix . $key);
  66     }
  67
  68     /**
  69      * In the simple case, this function will
  70      * get the cached value if available. If the entry
  71      * is not cached, it will try to get an exclusive
  72      * lock that announces that this process will
  73      * populate the cache.
  74      *
  75      * If we fail to get the lock -- this means another
  76      * process is doing it.
  77      * so we wait (block) for a few microseconds while we wait for
  78      * the cache to be filled or the lock to timeout.
  79      *
  80      * If you get a false from this call, you _must_
  81      * populate the cache ASAP or indicate that
  82      * you won't by calling releaseforfill().
  83      *
  84      * This technique forces serialisation and so helps deal
  85      * with thundering herd scenarios where a lot of clients
  86      * ask the for the same idempotent (and costly) operation.
  87      * The implementation is based on suggestions in this message
  88      * http://marc.theaimsgroup.com/?l=git&m=116562052506776&w=2
  89      *
  90      * @param $key string
  91      * @return mixed on cache hit, false otherwise
  92      */
  93     function getforfill ($key) {
  94         $get    = $this->mode . '_get';
  95         $lock   = $this->mode . '_lock';
  96
  97         $rec = $get($this->prefix . $key);
  98         if (!is_null($rec)) {
  99             return unserialize($rec);
 100         }
 101         if ($lock($this->prefix . $key . '_forfill')) {
 102             // we obtained the _forfill lock
 103             // our caller will compute and set the value
 104             return false;
 105         }
 106         // someone else has the lock
 107         // "block" till we can get the value
 108         // actually, loop .05s waiting for it
 109         for ($n=0;$n<5;$n++) {
 110             usleep(10000);
 111             $rec = $get($this->prefix . $key);
 112             if (!is_null($rec)) {
 113                 return unserialize($rec);
 114             }
 115         }
 116         return false;
 117     }
 118
 119     /**
 120      * Release the exclusive lock obtained by
 121      * getforfill(). See getforfill()
 122      * for more details.
 123      *
 124      * @param $key string
 125      * @return bool
 126      */
 127     function releaseforfill ($key) {
 128         $unlock = $this->mode . '_unlock';
 129         return $unlock($this->prefix . $key . '_forfill');
 130     }
 131 }
 132
 133 ?>