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             $this->mode = 'eaccelerator';
  26         } elseif (function_exists('mmcache_get')) {
  27             $this->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->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)) {
  57             return false;
  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 $key string
  90      * @return mixed on cache hit, false otherwise
  91      */
  92     function getforfill ($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 . $key . '_forfill')) {
 101             // we obtained the _forfill lock
 102             // our caller will compute and set the value
 103             return false;
 104         }
 105         // someone else has the lock
 106         // "block" till we can get the value
 107         // actually, loop .05s waiting for it
 108         for ($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         }
 115         return false;
 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 ?>