memcache.inc in Memcache API and Integration 7
Same filename and directory in other branches
File
memcache.incView source
<?php
/**
* @file
* Implementation of cache.inc with memcache logic included.
*/
require_once dirname(__FILE__) . '/dmemcache.inc';
/**
* Defines the period after which wildcard clears are not considered valid.
*/
define('MEMCACHE_WILDCARD_INVALIDATE', 86400 * 28);
define('MEMCACHE_CONTENT_CLEAR', 'MEMCACHE_CONTENT_CLEAR');
/**
* Implementation of cache.inc with memcache logic included
*/
class MemCacheDrupal implements DrupalCacheInterface {
protected $memcache;
/**
* Constructs a MemCacheDrupal object.
*
* @param string $bin
* The cache bin for which the object is created.
*/
public function __construct($bin) {
$this->memcache = dmemcache_object($bin);
$this->bin = $bin;
// If page_cache_without_database is enabled, we have to manually load the
// $conf array out of cache_bootstrap.
static $variables_loaded = FALSE;
// NOTE: We don't call drupal_get_bootstrap_phase() because this would
// break all 7.x Drupal installations prior to 7.33. For more information
// see https://www.drupal.org/node/667098.
if (drupal_bootstrap(NULL, FALSE) < DRUPAL_BOOTSTRAP_VARIABLES && !$variables_loaded) {
global $conf;
$variables_loaded = TRUE;
// Try loading variables from cache. If that fails, we have to bootstrap
// further in order to fetch them.
if ($cached = cache_get('variables', 'cache_bootstrap')) {
$variables = $cached->data;
// Make sure variable overrides are applied, see variable_initialize().
foreach ($conf as $name => $value) {
$variables[$name] = $value;
}
$conf = $variables;
}
else {
drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES, FALSE);
}
}
$this
->reloadVariables();
}
/**
* Implements DrupalCacheInterface::get().
*/
public function get($cid) {
// Clean up.
$this
->garbageCollection();
$cache = dmemcache_get($cid, $this->bin, $this->memcache);
return $this
->valid($cid, $cache) ? $cache : FALSE;
}
/**
* Implements DrupalCacheInterface::getMultiple().
*/
public function getMultiple(&$cids) {
// Clean up.
$this
->garbageCollection();
$results = dmemcache_get_multi($cids, $this->bin, $this->memcache);
foreach ($results as $cid => &$result) {
if (!$this
->valid($cid, $result)) {
// This object has expired, so don't return it.
unset($results[$cid]);
}
}
// Remove items from the referenced $cids array that we are returning,
// per the comment in cache_get_multiple() in includes/cache.inc.
$cids = array_diff($cids, array_keys($results));
return $results;
}
/**
* Garbage collection for get() and getMultiple().
*
* This functions check for session indicators to NOT use the cache. It
* checks if the last cache clearing time in there expired and if so unsets
* them, so anonymous users can get out of the "sessions" after some time, to
* get fast delivered pages (e.g. from Varnish etc. again).
*/
protected function garbageCollection() {
// Clean-up the per-user cache expiration session data, so that the session
// handler can properly clean-up the session data for anonymous users.
if (isset($_SESSION['cache_flush'])) {
foreach ($_SESSION['cache_flush'] as $bin => $timestamp) {
$expire = REQUEST_TIME - variable_get('cache_lifetime_' . $this->bin, variable_get('cache_lifetime', 0));
if ($timestamp < $expire) {
unset($_SESSION['cache_flush'][$bin]);
}
}
if (!$_SESSION['cache_flush']) {
unset($_SESSION['cache_flush']);
}
}
}
/**
* Checks if a retrieved cache item is valid.
*
* @param string $cid
* The cache id of the item
* @param mixed $cache
* The cache item, which will be updated if needed.
*
* @return bool
* Whether the item is valid.
*/
protected function valid($cid, &$cache) {
if ($cache) {
// Legacy support
if (!isset($cache->expire)) {
$cache->expire = CACHE_TEMPORARY;
}
if (!isset($cache->created)) {
$cache->created = 0;
}
// Session storage is used to simulate a cache clear for the current user
// when cache_lifetime is greater than 0.
$cache_tables = isset($_SESSION['cache_flush']) ? $_SESSION['cache_flush'] : NULL;
// Items that have expired are invalid. This includes CACHE_TEMPORARY
// items that were set prior to the last garbage collection, and
// timestamp set items.
//
// Test whether this cache has been garbage collected (general cache
// flush) longer ago than the cache_lifetime setting.
$cache_garbage_collected = $cache->created + $this->cache_lifetime <= $this->cache_temporary_flush;
// Depending on value of memcache_expire_wait_gc, test if a timestamp
// cached item has expired:
// If memcache_expired_wait_gc is true, this includes any timestamp items
// that expired more than cache_lifetime seconds before the last garbage
// collection. If memcache_expire_wait_gc is false, this includes any
// items that expired before present time.
$cache_timestamp_expired = variable_get('memcache_expire_wait_gc', FALSE) ? $cache->expire + $this->cache_lifetime <= $this->cache_temporary_flush : $cache->expire <= REQUEST_TIME;
// Test for expired items.
if ($cache->expire == CACHE_TEMPORARY && $cache_garbage_collected || $cache->expire > 0 && $cache_timestamp_expired) {
// If the memcache_stampede_protection variable is set, allow one
// process to rebuild the cache entry while serving expired content to
// the rest. Note that core happily returns expired cache items as valid
// and relies on cron to expire them, but this is mostly reliant on its
// use of CACHE_TEMPORARY which does not map well to memcache.
// @see http://drupal.org/node/534092
if (variable_get('memcache_stampede_protection', FALSE)) {
// The process that acquires the lock will get a cache miss, all
// others will get a cache hit.
if ($this
->lockInit() && $this
->stampedeProtected($cid) && lock_acquire("memcache_{$cid}:{$this->bin}", variable_get('memcache_stampede_semaphore', 15))) {
$cache = FALSE;
}
}
else {
$cache = FALSE;
}
}
elseif ($cache->created <= $this->cache_flush) {
$cache = FALSE;
}
elseif ($cache->expire != CACHE_PERMANENT && $cache->created + $this->cache_lifetime <= $this->cache_content_flush) {
$cache = FALSE;
}
elseif ($cache->expire != CACHE_PERMANENT && is_array($cache_tables) && isset($cache_tables[$this->bin]) && $cache_tables[$this->bin] >= $cache->created) {
// Cache item expired, return FALSE.
$cache = FALSE;
}
else {
if (!$this
->wildcardValid($cid, $cache)) {
$cache = FALSE;
}
}
}
// On cache misses, attempt to avoid stampedes when the
// memcache_stampede_protection variable is enabled.
if (!$cache) {
if (variable_get('memcache_stampede_protection', FALSE) && $this
->lockInit() && $this
->stampedeProtected($cid) && !lock_acquire("memcache_{$cid}:{$this->bin}", variable_get('memcache_stampede_semaphore', 15))) {
// Prevent any single request from waiting more than three times due to
// stampede protection. By default this is a maximum total wait of 15
// seconds. This accounts for two possibilities - a cache and lock miss
// more than once for the same item. Or a cache and lock miss for
// different items during the same request.
// @todo: it would be better to base this on time waited rather than
// number of waits, but the lock API does not currently provide this
// information. Currently the limit will kick in for three waits of 25ms
// or three waits of 5000ms.
static $lock_count = 0;
$lock_count++;
if ($lock_count <= variable_get('memcache_stampede_wait_limit', 3)) {
// The memcache_stampede_semaphore variable was used in previous
// releases of memcache, but the max_wait variable was not, so by
// default divide the semaphore value by 3 (5 seconds).
lock_wait("memcache_{$cid}:{$this->bin}", variable_get('memcache_stampede_wait_time', 5));
$cache = $this
->get($cid);
}
}
}
$valid = (bool) $cache;
if (variable_get('memcache_pagecache_header', FALSE) && $this->bin == 'cache_page') {
// Per RFC-6648, don't start with X-
$header = t('Drupal-Pagecache-Memcache: !status', array(
'!status' => $valid ? t('HIT') : t('MISS'),
));
if ($valid) {
$header .= t(', age=!age', array(
'!age' => REQUEST_TIME - $cache->created,
));
}
header($header);
}
return $valid;
}
/**
* Implements DrupalCacheInterface::set().
*/
public function set($cid, $data, $expire = CACHE_PERMANENT) {
$created_microtime = round(microtime(TRUE), 3);
// Positive expiration values of less than 30 days are seconds. Convert to
// an absolute timestamp.
if ($expire > 0 && $expire < 2592000) {
$expire = REQUEST_TIME + $expire;
}
// Create new cache object.
$cache = new stdClass();
$cache->cid = $cid;
$cache->data = is_object($data) ? clone $data : $data;
$cache->created = REQUEST_TIME;
$cache->created_microtime = $created_microtime;
$cache->expire = $expire;
// Record the previous number of wildcard flushes affecting our cid.
$cache->flushes = $this
->wildcardFlushes($cid);
// Determine stored memcache item lifetime.
if ($expire == CACHE_PERMANENT) {
// Set memcache item to never expire.
$memcache_expire = 0;
}
elseif (variable_get('memcache_expire_wait_gc', FALSE) || $expire == CACHE_TEMPORARY) {
// The cache_set() API states that an item set with a timestamp, once
// expired, behaves the same as CACHE_TEMPORARY: not removed till next
// general cache wipe (which is actually a garbage collection on each
// cache bin). However, the memcache module has traditionally treated
// timestamp-set items as expiring at that exact time. If
// memcache_expire_wait_gc is enabled, treat timestamp items the same as
// CACHE_TEMPORARY, and set the memcache expiration to something that
// keeps the item valid until the next garbage collection (30 days).
$memcache_expire = REQUEST_TIME + 2591999;
}
elseif (variable_get('memcache_stampede_protection', FALSE)) {
// If stampede protection is enabled, set the item expiration to twice
// its intended lifetime. The expired object may be served while one
// process rebuilds it.
$memcache_expire = REQUEST_TIME + ($expire - REQUEST_TIME) * 2;
}
else {
// Allow the memcache item to expire at the exact absolute timestamp.
$memcache_expire = $expire;
}
dmemcache_set($cid, $cache, $memcache_expire, $this->bin, $this->memcache);
// Release lock if acquired in $this->valid().
$lock = "memcache_{$cid}:{$this->bin}";
if (variable_get('memcache_stampede_protection', FALSE) && isset($GLOBALS['locks'][$lock])) {
lock_release("{$lock}");
}
}
/**
* Implements DrupalCacheInterface::clear().
*/
public function clear($cid = NULL, $wildcard = FALSE) {
if ($this->memcache === FALSE) {
// No memcache connection.
return;
}
// It is not possible to detect a cache_clear_all() call other than looking
// at the backtrace unless http://drupal.org/node/81461 is added.
$backtrace = debug_backtrace();
if ($cid == MEMCACHE_CONTENT_CLEAR || isset($backtrace[2]) && $backtrace[2]['function'] == 'cache_clear_all' && empty($backtrace[2]['args'])) {
// Update the timestamp of the last global flushing of this bin. When
// retrieving data from this bin, we will compare the cache creation
// time minus the cache_flush time to the cache_lifetime to determine
// whether or not the cached item is still valid.
$this->cache_content_flush = time();
$this
->variable_set('cache_content_flush_' . $this->bin, $this->cache_content_flush);
if (variable_get('cache_lifetime_' . $this->bin, variable_get('cache_lifetime', 0))) {
// We store the time in the current user's session. We then simulate
// that the cache was flushed for this user by not returning cached
// data to this user that was cached before the timestamp.
if (isset($_SESSION['cache_flush']) && is_array($_SESSION['cache_flush'])) {
$cache_bins = $_SESSION['cache_flush'];
}
else {
$cache_bins = array();
}
// Use time() rather than request time here for correctness.
$cache_tables[$this->bin] = $this->cache_content_flush;
$_SESSION['cache_flush'] = $cache_tables;
}
}
if (empty($cid) || $wildcard === TRUE) {
// system_cron() flushes all cache bins returned by hook_flush_caches()
// with cache_clear_all(NULL, $bin); The expected behaviour in this case
// is to perform garbage collection on expired cache items (which is
// irrelevant to memcache) but also to remove all CACHE_TEMPORARY items.
// @see https://api.drupal.org/api/drupal/includes!cache.inc/function/cache_clear_all/7
if (!isset($cid)) {
// Update the timestamp of the last CACHE_TEMPORARY clear. All
// temporary cache items created before this will be invalidated.
$this->cache_temporary_flush = time();
$this
->variable_set("cache_temporary_flush_{$this->bin}", $this->cache_temporary_flush);
// Return early here as we do not want to register a wildcard flush.
return;
}
elseif ($cid == '*') {
$cid = '';
}
if (empty($cid)) {
// Update the timestamp of the last global flushing of this bin. When
// retrieving data from this bin, we will compare the cache creation
// time minus the cache_flush time to the cache_lifetime to determine
// whether or not the cached item is still valid.
$this->cache_flush = time();
$this
->variable_set("cache_flush_{$this->bin}", $this->cache_flush);
$this->flushed = min($this->cache_flush, time() - $this->cache_lifetime);
if ($this->cache_lifetime) {
// We store the time in the current user's session which is saved into
// the sessions table by sess_write(). We then simulate that the
// cache was flushed for this user by not returning cached data to
// this user that was cached before the timestamp.
if (isset($_SESSION['cache_flush']) && is_array($_SESSION['cache_flush'])) {
$cache_bins = $_SESSION['cache_flush'];
}
else {
$cache_bins = array();
}
$cache_bins[$this->bin] = $this->cache_flush;
$_SESSION['cache_flush'] = $cache_bins;
}
}
else {
// Register a wildcard flush for current cid.
$this
->wildcards($cid, TRUE);
}
}
else {
$cids = is_array($cid) ? $cid : array(
$cid,
);
foreach ($cids as $cid) {
dmemcache_delete($cid, $this->bin, $this->memcache);
}
}
}
/**
* Sum of all matching wildcards.
*
* Checking any single cache item's flush value against this single-value sum
* tells us whether or not a new wildcard flush has affected the cached item.
*
* @param string $cid
* The cache id to check.
*
* @return int
* Sum of all matching wildcards for the given cache id.
*/
protected function wildcardFlushes($cid) {
return array_sum($this
->wildcards($cid));
}
/**
* Retrieves all matching wildcards for the given cache id.
*
* Utilize multiget to retrieve all possible wildcard matches, storing
* statically so multiple cache requests for the same item on the same page
* load doesn't add overhead.
*/
protected function wildcards($cid, $flush = FALSE) {
static $wildcards = array();
$matching = array();
if (!is_string($cid) && !is_int($cid)) {
register_shutdown_function('watchdog', 'memcache', 'Invalid cache id received in memcache.inc wildcards() of type !type.', array(
'!type' => gettype($cid),
), WATCHDOG_ERROR);
return $matching;
}
$length = strlen($cid);
if (isset($this->wildcard_flushes[$this->bin]) && is_array($this->wildcard_flushes[$this->bin])) {
// Wildcard flushes per table are keyed by a substring equal to the
// shortest wildcard clear on the table so far. So if the shortest
// wildcard was "links:foo:", and the cid we're checking for is
// "links:bar:bar", then the key will be "links:bar:".
$keys = array_keys($this->wildcard_flushes[$this->bin]);
$wildcard_length = strlen(reset($keys));
$wildcard_key = substr($cid, 0, $wildcard_length);
// Determine which lookups we need to perform to determine whether or not
// our cid was impacted by a wildcard flush.
$lookup = array();
// Find statically cached wildcards, and determine possibly matching
// wildcards for this cid based on a history of the lengths of past
// valid wildcard flushes in this bin.
if (isset($this->wildcard_flushes[$this->bin][$wildcard_key])) {
foreach ($this->wildcard_flushes[$this->bin][$wildcard_key] as $flush_length => $timestamp) {
if ($length >= $flush_length && $timestamp >= REQUEST_TIME - $this->invalidate) {
$wildcard = '.wildcard-' . substr($cid, 0, $flush_length);
if (isset($wildcards[$this->bin][$wildcard])) {
$matching[$wildcard] = $wildcards[$this->bin][$wildcard];
}
else {
$lookup[$wildcard] = $wildcard;
}
}
}
}
// Do a multi-get to retrieve all possibly matching wildcard flushes.
if (!empty($lookup)) {
$values = dmemcache_get_multi($lookup, $this->bin, $this->memcache);
if (is_array($values)) {
// Prepare an array of matching wildcards.
$matching = array_merge($matching, $values);
// Store matches in the static cache.
if (isset($wildcards[$this->bin])) {
$wildcards[$this->bin] = array_merge($wildcards[$this->bin], $values);
}
else {
$wildcards[$this->bin] = $values;
}
$lookup = array_diff_key($lookup, $values);
}
// Also store failed lookups in our static cache, so we don't have to
// do repeat lookups on single page loads.
foreach ($lookup as $key => $key) {
$wildcards[$this->bin][$key] = 0;
}
}
}
if ($flush) {
$key_length = $length;
if (isset($this->wildcard_flushes[$this->bin])) {
$keys = array_keys($this->wildcard_flushes[$this->bin]);
$key_length = strlen(reset($keys));
}
$key = substr($cid, 0, $key_length);
// Avoid too many calls to variable_set() by only recording a flush for
// a fraction of the wildcard invalidation variable, per cid length.
// Defaults to 28 / 4, or one week.
if (!isset($this->wildcard_flushes[$this->bin][$key][$length]) || REQUEST_TIME - $this->wildcard_flushes[$this->bin][$key][$length] > $this->invalidate / 4) {
// If there are more than 50 different wildcard keys for this bin
// shorten the key by one, this should reduce variability by
// an order of magnitude and ensure we don't use too much memory.
if (isset($this->wildcard_flushes[$this->bin]) && count($this->wildcard_flushes[$this->bin]) > 50) {
$key = substr($cid, 0, $key_length - 1);
$length = strlen($key);
}
// If this is the shortest key length so far, we need to remove all
// other wildcards lengths recorded so far for this bin and start
// again. This is equivalent to a full cache flush for this table, but
// it ensures the minimum possible number of wildcards are requested
// along with cache consistency.
if ($length < $key_length) {
$this->wildcard_flushes[$this->bin] = array();
$this
->variable_set("cache_flush_{$this->bin}", time());
$this->cache_flush = time();
}
$key = substr($cid, 0, $key_length);
$this->wildcard_flushes[$this->bin][$key][$length] = REQUEST_TIME;
variable_set('memcache_wildcard_flushes', $this->wildcard_flushes);
}
$key = '.wildcard-' . $cid;
if (isset($wildcards[$this->bin][$key])) {
$wildcards[$this->bin][$key]++;
}
else {
$wildcards[$this->bin][$key] = 1;
}
dmemcache_set($key, $wildcards[$this->bin][$key], 0, $this->bin);
}
return $matching;
}
/**
* Check if a wildcard flush has invalidated the current cached copy.
*/
protected function wildcardValid($cid, $cache) {
// Previously cached content won't have ->flushes defined. We could
// force flush, but instead leave this up to the site admin.
$flushes = isset($cache->flushes) ? (int) $cache->flushes : 0;
if ($flushes < (int) $this
->wildcardFlushes($cid)) {
return FALSE;
}
return TRUE;
}
/**
* Implements DrupalCacheInterface::isEmpty().
*/
public function isEmpty() {
// We do not know so err on the safe side?
return FALSE;
}
/**
* Helper function to load locking framework if not already loaded.
*
* @return bool
* Whether the locking system was initialized successfully. This must always
* return TRUE or throw an exception.
*/
public function lockInit() {
// On a cache miss when page_cache_without_database is enabled, we can end
// up here without the lock system being initialized. Bootstrap drupal far
// enough to load the lock system.
if (!function_exists('lock_acquire')) {
drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES, FALSE);
}
if (!function_exists('lock_acquire')) {
// Bootstrap failed, log error.
register_shutdown_function('watchdog', 'memcache', 'Bootstrap failed in lockInit(), lock_acquire() is not available. (phase:!phase)', array(
'!phase' => drupal_get_bootstrap_phase(),
), WATCHDOG_ERROR);
return FALSE;
}
return TRUE;
}
/**
* Determines whether stampede protection is enabled for a given bin/cid.
*
* Memcache stampede protection is primarily designed to benefit the following
* caching pattern: a miss on a cache_get for a specific cid is immediately
* followed by a cache_set for that cid. In cases where this pattern is not
* followed, stampede protection can be disabled to avoid long hanging locks.
* For example, a cache miss in Drupal core's module_implements() won't
* execute a cache_set until drupal_page_footer() calls
* module_implements_write_cache() which can occur much later in page
* generation.
*
* @param string $cid
* The cache id of the data to retrieve.
*
* @return bool
* Returns TRUE if stampede protection is enabled for that particular cache
* bin/cid, otherwise FALSE.
*/
protected function stampedeProtected($cid) {
$ignore_settings = variable_get('memcache_stampede_protection_ignore', array(
// Disable stampede protection for specific cids in 'cache_bootstrap'.
'cache_bootstrap' => array(
// The module_implements cache is written after finishing the request.
'module_implements',
// Variables have their own lock protection.
'variables',
// Delayed set.
'lookup_cache',
// Both schema and the theme_registry uses DrupalCacheArray, which sets
// the cache entry with a class destructor.
'schema:runtime:*',
'theme_registry:runtime:*',
// Not written until the end of drupal_page_footer()
'_drupal_file_scan_cache',
),
// Disable stampede protection for cid prefix in 'cache'.
'cache' => array(
// I18n uses a class destructor to set the cache.
'i18n:string:*',
),
// Delayed set.
'cache_path',
// Disable stampede protection for the contrib cache_rules bin as recent
// versions of the rules module provides its own stampede protection.
'cache_rules',
));
// Support ignoring an entire bin.
if (in_array($this->bin, $ignore_settings)) {
return FALSE;
}
// Support ignoring by cids.
if (isset($ignore_settings[$this->bin])) {
// Support ignoring specific cids.
if (in_array($cid, $ignore_settings[$this->bin])) {
return FALSE;
}
// Support ignoring cids starting with a suffix.
foreach ($ignore_settings[$this->bin] as $ignore) {
$split = explode('*', $ignore);
if (count($split) > 1 && strpos($cid, $split[0]) === 0) {
return FALSE;
}
}
}
return TRUE;
}
/**
* Helper function to reload variables.
*
* This is used by the tests to verify that the cache object used the correct
* settings.
*/
public function reloadVariables() {
$this->wildcard_flushes = variable_get('memcache_wildcard_flushes', array());
$this->invalidate = variable_get('memcache_wildcard_invalidate', MEMCACHE_WILDCARD_INVALIDATE);
$this->cache_lifetime = variable_get('cache_lifetime_' . $this->bin, variable_get('cache_lifetime', 0));
$this->cache_flush = variable_get('cache_flush_' . $this->bin);
$this->cache_content_flush = variable_get('cache_content_flush_' . $this->bin, 0);
$this->cache_temporary_flush = variable_get('cache_temporary_flush_' . $this->bin, 0);
$this->flushed = min($this->cache_flush, REQUEST_TIME - $this->cache_lifetime);
}
/**
* Re-implementation of variable_set() that writes through instead of clearing.
*/
public function variable_set($name, $value) {
global $conf;
// If the value appears unchanged, do nothing.
if (isset($conf[$name]) && $conf[$name] === $value) {
return;
}
// When lots of writes happen in a short period of time db_merge can throw
// errors. This should only happen if another request has written the
// variable first, so we catch the error to prevent a fatal error.
try {
db_merge('variable')
->key(array(
'name' => $name,
))
->fields(array(
'value' => serialize($value),
))
->execute();
} catch (Exception $e) {
// We can safely ignore the error, since it's likely a cache flush
// timestamp which should still be accurate.
}
// If the variables are cached, get a fresh copy, update with the new value
// and set it again.
if ($cached = cache_get('variables', 'cache_bootstrap')) {
$variables = $cached->data;
$variables[$name] = $value;
cache_set('variables', $variables, 'cache_bootstrap');
}
// If the variables aren't cached, there's no need to do anything.
$conf[$name] = $value;
}
}Constants
Name |
Description |
|---|---|
| MEMCACHE_CONTENT_CLEAR | |
| MEMCACHE_WILDCARD_INVALIDATE | Defines the period after which wildcard clears are not considered valid. |
Classes
|
Name |
Description |
|---|---|
| MemCacheDrupal | Implementation of cache.inc with memcache logic included |