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<?php
/**
* @file
* Functions and interfaces for cache handling.
*/
/**
* Gets the cache object for a cache bin.
*
* By default, this returns an instance of the DrupalDatabaseCache class.
* Classes implementing DrupalCacheInterface can register themselves both as a
* default implementation and for specific bins.
*
* @param $bin
* The cache bin for which the cache object should be returned.
* @return DrupalCacheInterface
* The cache object associated with the specified bin.
*
* @see DrupalCacheInterface
*/
function _cache_get_object($bin) {
// We do not use drupal_static() here because we do not want to change the
// storage of a cache bin mid-request.
static $cache_objects;
if (!isset($cache_objects[$bin])) {
$class = variable_get('cache_class_' . $bin);
if (!isset($class)) {
$class = variable_get('cache_default_class', 'DrupalDatabaseCache');
}
$cache_objects[$bin] = new $class($bin);
}
return $cache_objects[$bin];
}
/**
* Returns data from the persistent cache.
*
* Data may be stored as either plain text or as serialized data. cache_get
* will automatically return unserialized objects and arrays.
*
* @param $cid
* The cache ID of the data to retrieve.
* @param $bin
* The cache bin to store the data in. Valid core values are 'cache_block',
* 'cache_bootstrap', 'cache_field', 'cache_filter', 'cache_form',
* 'cache_menu', 'cache_page', 'cache_path', 'cache_update' or 'cache' for
* the default cache.
*
* @return
* The cache or FALSE on failure.
*
* @see cache_set()
*/
function cache_get($cid, $bin = 'cache') {
return _cache_get_object($bin)->get($cid);
}
/**
* Returns data from the persistent cache when given an array of cache IDs.
*
* @param $cids
* An array of cache IDs for the data to retrieve. This is passed by
* reference, and will have the IDs successfully returned from cache removed.
* @param $bin
* The cache bin where the data is stored.
*
* @return
* An array of the items successfully returned from cache indexed by cid.
*/
function cache_get_multiple(array &$cids, $bin = 'cache') {
return _cache_get_object($bin)->getMultiple($cids);
}
/**
* Stores data in the persistent cache.
*
* The persistent cache is split up into several cache bins. In the default
* cache implementation, each cache bin corresponds to a database table by the
* same name. Other implementations might want to store several bins in data
* structures that get flushed together. While it is not a problem for most
* cache bins if the entries in them are flushed before their expire time, some
* might break functionality or are extremely expensive to recalculate. These
* will be marked with a (*). The other bins expired automatically by core.
* Contributed modules can add additional bins and get them expired
* automatically by implementing hook_flush_caches().
*
* - cache: Generic cache storage bin (used for variables, theme registry,
* locale date, list of simpletest tests etc).
*
* - cache_block: Stores the content of various blocks.
*
* - cache field: Stores the field data belonging to a given object.
*
* - cache_filter: Stores filtered pieces of content.
*
* - cache_form(*): Stores multistep forms. Flushing this bin means that some
* forms displayed to users lose their state and the data already submitted
* to them.
*
* - cache_menu: Stores the structure of visible navigation menus per page.
*
* - cache_page: Stores generated pages for anonymous users. It is flushed
* very often, whenever a page changes, at least for every ode and comment
* submission. This is the only bin affected by the page cache setting on
* the administrator panel.
*
* - cache path: Stores the system paths that have an alias.
*
* - cache update(*): Stores available releases. The update server (for
* example, drupal.org) needs to produce the relevant XML for every project
* installed on the current site. As this is different for (almost) every
* site, it's very expensive to recalculate for the update server.
*
* The reasons for having several bins are as follows:
*
* - smaller bins mean smaller database tables and allow for faster selects and
* inserts
* - we try to put fast changing cache items and rather static ones into
* different bins. The effect is that only the fast changing bins will need a
* lot of writes to disk. The more static bins will also be better cacheable
* with MySQL's query cache.
*
* @param $cid
* The cache ID of the data to store.
* @param $data
* The data to store in the cache. Complex data types will be automatically
* serialized before insertion.
* Strings will be stored as plain text and not serialized.
* @param $bin
* The cache bin to store the data in. Valid core values are 'cache_block',
* 'cache_bootstrap', 'cache_field', 'cache_filter', 'cache_form',
* 'cache_menu', 'cache_page', 'cache_update' or 'cache' for the default
* cache.
* @param $expire
* One of the following values:
* - CACHE_PERMANENT: Indicates that the item should never be removed unless
* explicitly told to using cache_clear_all() with a cache ID.
* - CACHE_TEMPORARY: Indicates that the item should be removed at the next
* general cache wipe.
* - A Unix timestamp: Indicates that the item should be kept at least until
* the given time, after which it behaves like CACHE_TEMPORARY.
*
* @see cache_get()
*/
function cache_set($cid, $data, $bin = 'cache', $expire = CACHE_PERMANENT) {
return _cache_get_object($bin)->set($cid, $data, $expire);
}
/**
* Expires data from the cache.
*
* If called without arguments, expirable entries will be cleared from the
* cache_page and cache_block bins.
*
* @param $cid
* If set, the cache ID to delete. Otherwise, all cache entries that can
* expire are deleted.
* @param $bin
* If set, the cache bin to delete from. Mandatory argument if $cid is set.
* @param $wildcard
* If TRUE, cache IDs starting with $cid are deleted in addition to the
* exact cache ID specified by $cid. If $wildcard is TRUE and $cid is '*',
* the entire cache bin is emptied.
*/
function cache_clear_all($cid = NULL, $bin = NULL, $wildcard = FALSE) {
if (!isset($cid) && !isset($bin)) {
// Clear the block cache first, so stale data will
// not end up in the page cache.
if (module_exists('block')) {
cache_clear_all(NULL, 'cache_block');
}
cache_clear_all(NULL, 'cache_page');
return;
}
return _cache_get_object($bin)->clear($cid, $wildcard);
}
/**
* Checks if a cache bin is empty.
*
* A cache bin is considered empty if it does not contain any valid data for any
* cache ID.
*
* @param $bin
* The cache bin to check.
*
* @return
* TRUE if the cache bin specified is empty.
*/
function cache_is_empty($bin) {
return _cache_get_object($bin)->isEmpty();
}
/**
* Defines an interface for cache implementations.
*
* All cache implementations have to implement this interface.
* DrupalDatabaseCache provides the default implementation, which can be
* consulted as an example.
*
* To make Drupal use your implementation for a certain cache bin, you have to
* set a variable with the name of the cache bin as its key and the name of
* your class as its value. For example, if your implementation of
* DrupalCacheInterface was called MyCustomCache, the following line would make
* Drupal use it for the 'cache_page' bin:
* @code
* variable_set('cache_class_cache_page', 'MyCustomCache');
* @endcode
*
* Additionally, you can register your cache implementation to be used by
* default for all cache bins by setting the variable 'cache_default_class' to
* the name of your implementation of the DrupalCacheInterface, e.g.
* @code
* variable_set('cache_default_class', 'MyCustomCache');
* @endcode
*
* To implement a completely custom cache bin, use the same variable format:
* @code
* variable_set('cache_class_custom_bin', 'MyCustomCache');
* @endcode
* To access your custom cache bin, specify the name of the bin when storing
* or retrieving cached data:
* @code
* cache_set($cid, $data, 'custom_bin', $expire);
* cache_get($cid, 'custom_bin');
* @endcode
*
* @see _cache_get_object()
* @see DrupalDatabaseCache
*/
interface DrupalCacheInterface {
/**
* Constructs a new cache interface.
*
* @param $bin
* The cache bin for which the object is created.
*/
function __construct($bin);
/**
* Returns data from the persistent cache.
*
* Data may be stored as either plain text or as serialized data. cache_get()
* will automatically return unserialized objects and arrays.
*
* @param $cid
* The cache ID of the data to retrieve.
*
* @return
* The cache or FALSE on failure.
*/
function get($cid);
/**
* Returns data from the persistent cache when given an array of cache IDs.
*
* @param $cids
* An array of cache IDs for the data to retrieve. This is passed by
* reference, and will have the IDs successfully returned from cache
* removed.
*
* @return
* An array of the items successfully returned from cache indexed by cid.
*/
function getMultiple(&$cids);
/**
* Stores data in the persistent cache.
*
* @param $cid
* The cache ID of the data to store.
* @param $data
* The data to store in the cache. Complex data types will be automatically
* serialized before insertion.
* Strings will be stored as plain text and not serialized.
* @param $expire
* One of the following values:
* - CACHE_PERMANENT: Indicates that the item should never be removed unless
* explicitly told to using cache_clear_all() with a cache ID.
* - CACHE_TEMPORARY: Indicates that the item should be removed at the next
* general cache wipe.
* - A Unix timestamp: Indicates that the item should be kept at least until
* the given time, after which it behaves like CACHE_TEMPORARY.
*/
function set($cid, $data, $expire = CACHE_PERMANENT);
/**
* Expires data from the cache.
*
* If called without arguments, expirable entries will be cleared from the
* cache_page and cache_block bins.
*
* @param $cid
* If set, the cache ID to delete. Otherwise, all cache entries that can
* expire are deleted.
* @param $wildcard
* If set to TRUE, the $cid is treated as a substring
* to match rather than a complete ID. The match is a right hand
* match. If '*' is given as $cid, the bin $bin will be emptied.
*/
function clear($cid = NULL, $wildcard = FALSE);
/**
* Checks if a cache bin is empty.
*
* A cache bin is considered empty if it does not contain any valid data for
* any cache ID.
*
* @return
* TRUE if the cache bin specified is empty.
*/
function isEmpty();
}
/**
* Defines a default cache implementation.
*
* This is Drupal's default cache implementation. It uses the database to store
* cached data. Each cache bin corresponds to a database table by the same name.
*/
class DrupalDatabaseCache implements DrupalCacheInterface {
protected $bin;
/**
* Constructs a new DrupalDatabaseCache object.
*/
function __construct($bin) {
$this->bin = $bin;
}
/**
* Implements DrupalCacheInterface::get().
*/
function get($cid) {
$cids = array($cid);
$cache = $this->getMultiple($cids);
return reset($cache);
}
/**
* Implements DrupalCacheInterface::getMultiple().
*/
function getMultiple(&$cids) {
try {
// Garbage collection necessary when enforcing a minimum cache lifetime.
$this->garbageCollection($this->bin);
// When serving cached pages, the overhead of using db_select() was found
// to add around 30% overhead to the request. Since $this->bin is a
// variable, this means the call to db_query() here uses a concatenated
// string. This is highly discouraged under any other circumstances, and
// is used here only due to the performance overhead we would incur
// otherwise. When serving an uncached page, the overhead of using
// db_select() is a much smaller proportion of the request.
$result = db_query('SELECT cid, data, created, expire, serialized FROM {' . db_escape_table($this->bin) . '} WHERE cid IN (:cids)', array(':cids' => $cids));
$cache = array();
foreach ($result as $item) {
$item = $this->prepareItem($item);
if ($item) {
$cache[$item->cid] = $item;
}
}
$cids = array_diff($cids, array_keys($cache));
return $cache;
}
catch (Exception $e) {
// If the database is never going to be available, cache requests should
// return FALSE in order to allow exception handling to occur.
return array();
}
}
/**
* Garbage collection for get() and getMultiple().
*
* @param $bin
* The bin being requested.
*/
protected function garbageCollection() {
$cache_lifetime = variable_get('cache_lifetime', 0);
// Clean-up the per-user cache expiration session data, so that the session
// handler can properly clean-up the session data for anonymous users.
if (isset($_SESSION['cache_expiration'])) {
$expire = REQUEST_TIME - $cache_lifetime;
foreach ($_SESSION['cache_expiration'] as $bin => $timestamp) {
if ($timestamp < $expire) {
unset($_SESSION['cache_expiration'][$bin]);
}
}
if (!$_SESSION['cache_expiration']) {
unset($_SESSION['cache_expiration']);
}
}
// Garbage collection of temporary items is only necessary when enforcing
// a minimum cache lifetime.
if (!$cache_lifetime) {
return;
}
// When cache lifetime is in force, avoid running garbage collection too
// often since this will remove temporary cache items indiscriminately.
$cache_flush = variable_get('cache_flush_' . $this->bin, 0);
if ($cache_flush && ($cache_flush + $cache_lifetime <= REQUEST_TIME)) {
// Reset the variable immediately to prevent a meltdown in heavy load situations.
variable_set('cache_flush_' . $this->bin, 0);
// Time to flush old cache data
db_delete($this->bin)
->condition('expire', CACHE_PERMANENT, '<>')
->condition('expire', $cache_flush, '<=')
->execute();
}
}
/**
* Prepares a cached item.
*
* Checks that items are either permanent or did not expire, and unserializes
* data as appropriate.
*
* @param $cache
* An item loaded from cache_get() or cache_get_multiple().
*
* @return
* The item with data unserialized as appropriate or FALSE if there is no
* valid item to load.
*/
protected function prepareItem($cache) {
global $user;
if (!isset($cache->data)) {
return FALSE;
}
// If the cached data is temporary and subject to a per-user minimum
// lifetime, compare the cache entry timestamp with the user session
// cache_expiration timestamp. If the cache entry is too old, ignore it.
if ($cache->expire != CACHE_PERMANENT && variable_get('cache_lifetime', 0) && isset($_SESSION['cache_expiration'][$this->bin]) && $_SESSION['cache_expiration'][$this->bin] > $cache->created) {
// Ignore cache data that is too old and thus not valid for this user.
return FALSE;
}
// If the data is permanent or not subject to a minimum cache lifetime,
// unserialize and return the cached data.
if ($cache->serialized) {
$cache->data = unserialize($cache->data);
}
return $cache;
}
/**
* Implements DrupalCacheInterface::set().
*/
function set($cid, $data, $expire = CACHE_PERMANENT) {
$fields = array(
'serialized' => 0,
'created' => REQUEST_TIME,
'expire' => $expire,
);
if (!is_string($data)) {
$fields['data'] = serialize($data);
$fields['serialized'] = 1;
}
else {
$fields['data'] = $data;
$fields['serialized'] = 0;
}
try {
db_merge($this->bin)
->key(array('cid' => $cid))
->fields($fields)
->execute();
}
catch (Exception $e) {
// The database may not be available, so we'll ignore cache_set requests.
}
}
/**
* Implements DrupalCacheInterface::clear().
*/
function clear($cid = NULL, $wildcard = FALSE) {
global $user;
if (empty($cid)) {
if (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 that was cached before the timestamp.
$_SESSION['cache_expiration'][$this->bin] = REQUEST_TIME;
$cache_flush = variable_get('cache_flush_' . $this->bin, 0);
if ($cache_flush == 0) {
// This is the first request to clear the cache, start a timer.
variable_set('cache_flush_' . $this->bin, REQUEST_TIME);
}
elseif (REQUEST_TIME > ($cache_flush + variable_get('cache_lifetime', 0))) {
// Clear the cache for everyone, cache_lifetime seconds have
// passed since the first request to clear the cache.
db_delete($this->bin)
->condition('expire', CACHE_PERMANENT, '<>')
->condition('expire', REQUEST_TIME, '<')
->execute();
variable_set('cache_flush_' . $this->bin, 0);
}
}
else {
// No minimum cache lifetime, flush all temporary cache entries now.
db_delete($this->bin)
->condition('expire', CACHE_PERMANENT, '<>')
->condition('expire', REQUEST_TIME, '<')
->execute();
}
}
else {
if ($wildcard) {
if ($cid == '*') {
db_truncate($this->bin)->execute();
}
else {
db_delete($this->bin)
->condition('cid', db_like($cid) . '%', 'LIKE')
->execute();
}
}
elseif (is_array($cid)) {
// Delete in chunks when a large array is passed.
do {
db_delete($this->bin)
->condition('cid', array_splice($cid, 0, 1000), 'IN')
->execute();
}
while (count($cid));
}
else {
db_delete($this->bin)
->condition('cid', $cid)
->execute();
}
}
}
/**
* Implements DrupalCacheInterface::isEmpty().
*/
function isEmpty() {
$this->garbageCollection();
$query = db_select($this->bin);
$query->addExpression('1');
$result = $query->range(0, 1)
->execute()
->fetchField();
return empty($result);
}
}
