dmemcache.inc in Memcache API and Integration 5

File

dmemcache.inc

<?php

/*
 * Core dmemcache functions required by:
 *   memcache.inc
 *   memcache.db.inc
 *   session-memcache.inc
 *   session-memcache.db.inc
 */
global $_memcache_statistics;
$_memcache_statistics = array(
  'get' => array(),
  'set' => array(),
  'hit' => array(),
);

/*
 * A memcache API for Drupal.
 */

/**
 *  Place an item into memcache
 *
 * @param $key The string with with you will retrieve this item later.
 * @param $value The item to be stored.
 * @param $exp Parameter expire is expiration time in seconds. If it's 0, the item never expires
 *   (but memcached server doesn't guarantee this item to be stored all the time, it could be
 *   deleted from the cache to make place for other items).
 * @param $bin The name of the Drupal subsystem that is making this call. Examples could be
 *   'cache', 'alias', 'taxonomy term' etc. It is possible to map different $bin values to
 *   different memcache servers.
 *
 * @return bool
 */
function dmemcache_set($key, $value, $exp = 0, $bin = 'cache') {
  global $_memcache_statistics;
  $_memcache_statistics['set'][] = $key;
  $_memcache_statistics['bins'][] = $bin;
  if ($mc = dmemcache_object($bin)) {
    $full_key = dmemcache_key($key, $bin);
    if (!$mc
      ->set($full_key, $value, MEMCACHE_COMPRESSED, $exp)) {
      return FALSE;
    }
    else {
      return TRUE;
    }
  }
  return FALSE;
}

/**
 * Retrieve a value from the cache.
 *
 * @param $key The key with which the item was stored.
 * @param $bin The bin in which the item was stored.
 *
 * @return The item which was originally saved or FALSE
 */
function dmemcache_get($key, $bin = 'cache') {
  global $_memcache_statistics;
  $_memcache_statistics['get'][] = $key;
  $_memcache_statistics['bins'][] = $bin;
  if ($mc = dmemcache_object($bin)) {
    $full_key = dmemcache_key($key, $bin);
    $result = $mc
      ->get($full_key);
    if ($result) {

      // We check $result->expire to see if the object has expired.  If so, we
      // try and grab a lock.  If we get the lock, we return FALSE instead of
      // the cached object which should cause it to be rebuilt.  If we do not
      // get the lock, we return the cached object.  The goal here is to avoid
      // cache stampedes.
      // By default the cache stampede semaphore is held for 15 seconds.  This
      // can be adjusted by setting the memcache_stampede_semaphore variable.
      // TODO: Can we log when a sempahore expires versus being intentionally
      // freed to track when this is happening?
      if (isset($result->expire) && $result->expire <= $_SERVER['REQUEST_TIME'] && $mc
        ->add($full_key . '_semaphore', '', FALSE, variable_get('memcache_stampede_semaphore', 15))) {
        $result = FALSE;
      }
      else {
        $_memcache_statistics['hit'][] = $key;
      }
    }
    return $result;
  }
}

/**
 * Deletes an item from the cache.
 *
 * @param $key The key with which the item was stored.
 * @param $bin The bin in which the item was stored.
 *
 * @return Returns TRUE on success or FALSE on failure.
 */
function dmemcache_delete($key, $bin = 'cache') {
  if ($mc = dmemcache_object($bin)) {
    $full_key = dmemcache_key($key, $bin);
    return $mc
      ->delete($full_key);
  }
  return FALSE;
}

/**
 * Immediately invalidates all existing items. dmemcache_flush doesn't actually free any
 * resources, it only marks all the items as expired, so occupied memory will be overwritten by
 * new items.
 *
 * @param $bin The bin to flush. Note that this will flush all bins mapped to the same server
 *   as $bin. There is no way at this time to empty just one bin.
 *
 * @return Returns TRUE on success or FALSE on failure.
 */
function dmemcache_flush($bin = 'cache') {
  if ($mc = dmemcache_object($bin)) {
    return $mc
      ->flush();
  }
}
function dmemcache_stats($bin = 'cache', $type = '') {

  // resolve requests for 'default' type to ''
  if ($type == 'default') {
    $type = '';
  }

  // resolve requests for 'default' bin to 'cache'.
  if ($bin == 'default') {
    $bin = 'cache';
  }
  if ($mc = dmemcache_object($bin)) {
    return $mc
      ->getExtendedStats($type);
  }
}

/**
 * Returns an Memcache object based on the bin requested. Note that there is
 * nothing preventing developers from calling this function directly to get the
 * Memcache object. Do this if you need functionality not provided by this API
 * or if you need to use legacy code. Otherwise, use the dmemcache (get, set,
 * delete, flush) API functions provided here.
 *
 * @param $bin The bin which is to be used.
 *
 * @param $flush Rebuild the bin/server/cache mapping.
 *
 * @return an Memcache object or FALSE.
 */
function dmemcache_object($bin = NULL, $flush = FALSE) {
  static $memcacheCache = array(), $memcache_servers, $memcache_bins;
  if ($flush) {
    foreach ($memcacheCache as $cluster) {
      $cluster
        ->close();
    }
    $memcacheCache = array();
  }
  if (empty($memcacheCache) || empty($memcacheCache[$bin])) {

    // $memcache_servers and $memcache_bins originate from settings.php.
    // $memcache_servers_custom and $memcache_bins_custom get set by
    // memcache.module. They are then merged into $memcache_servers and
    // $memcache_bins, which are statically cached for performance.
    if (empty($memcache_servers)) {

      // Values from settings.php
      $memcache_servers = variable_get('memcache_servers', array(
        '127.0.0.1:11211' => 'default',
      ));
      $memcache_bins = variable_get('memcache_bins', array(
        'cache' => 'default',
      ));
    }

    // If there is no cluster for this bin in $memcache_bins, cluster is 'default'.
    $cluster = empty($memcache_bins[$bin]) ? 'default' : $memcache_bins[$bin];

    // If this bin isn't in our $memcache_bins configuration array, and the
    // 'default' cluster is already initialized, map the bin to 'cache' because
    // we always map the 'cache' bin to the 'default' cluster.
    if (empty($memcache_bins[$bin]) && !empty($memcacheCache['cache'])) {
      $memcacheCache[$bin] =& $memcacheCache['cache'];
    }
    else {

      // Create a new Memcache object. Each cluster gets its own Memcache object.
      $memcache = new Memcache();

      // A variable to track whether we've connected to the first server.
      $init = FALSE;

      // Link all the servers to this cluster.
      foreach ($memcache_servers as $s => $c) {
        if ($c == $cluster) {
          list($host, $port) = explode(':', $s);

          // This is a server that belongs to this cluster.
          if (!$init) {

            // First server gets the connect.
            if (@$memcache
              ->addServer($host, $port)) {

              // Only set init to true if a connection was made.
              $init = TRUE;
            }
          }
          else {

            // Subsequent servers gett addServer.
            @$memcache
              ->addServer($host, $port);
          }
        }
      }
      if ($init) {

        // Map the current bin with the new Memcache object.
        $memcacheCache[$bin] = $memcache;

        // Now that all the servers have been mapped to this cluster, look for
        // other bins that belong to the cluster and map them too.
        foreach ($memcache_bins as $b => $c) {
          if ($c == $cluster && $b != $bin) {

            // Map this bin and cluster by reference.
            $memcacheCache[$b] =& $memcacheCache[$bin];
          }
        }
      }
    }
  }
  return empty($memcacheCache[$bin]) ? FALSE : $memcacheCache[$bin];
}
function dmemcache_key($key, $bin = 'cache') {
  static $prefix;

  // memcache_key_prefix can be set in settings.php to support site namespaces
  // in a multisite environment.
  if (empty($prefix)) {
    $prefix = variable_get('memcache_key_prefix', '');
  }
  $full_key = ($prefix ? $prefix . '-' : '') . $bin . '-' . $key;
  return urlencode($full_key);
}

Functions

Name	Description
dmemcache_delete	Deletes an item from the cache.
dmemcache_flush	Immediately invalidates all existing items. dmemcache_flush doesn't actually free any resources, it only marks all the items as expired, so occupied memory will be overwritten by new items.
dmemcache_get	Retrieve a value from the cache.
dmemcache_key
dmemcache_object	Returns an Memcache object based on the bin requested. Note that there is nothing preventing developers from calling this function directly to get the Memcache object. Do this if you need functionality not provided by this API or if you need to use…
dmemcache_set	Place an item into memcache
dmemcache_stats

Globals

Name	Description
$_memcache_statistics