diff --git a/core/core.services.yml b/core/core.services.yml
index 93231810fe2c072e3caad08adad8d164b4fdbe55..e15618ff1ba6c7f2c38505f2373ca459a399effc 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -25,6 +25,8 @@ services:
cache.backend.database:
class: Drupal\Core\Cache\DatabaseBackendFactory
arguments: ['@database']
+ cache.backend.apcu:
+ class: Drupal\Core\Cache\ApcuBackendFactory
cache.backend.php:
class: Drupal\Core\Cache\PhpBackendFactory
cache.backend.memory:
diff --git a/core/lib/Drupal/Core/Cache/ApcuBackend.php b/core/lib/Drupal/Core/Cache/ApcuBackend.php
new file mode 100644
index 0000000000000000000000000000000000000000..2d9275b947267bf2314096656eccf654c93bcb42
--- /dev/null
+++ b/core/lib/Drupal/Core/Cache/ApcuBackend.php
@@ -0,0 +1,377 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Cache\ApcuBackend.
+ */
+
+namespace Drupal\Core\Cache;
+
+/**
+ * Stores cache items in the Alternative PHP Cache User Cache (APCu).
+ */
+class ApcuBackend implements CacheBackendInterface {
+
+ /**
+ * The name of the cache bin to use.
+ *
+ * @var string
+ */
+ protected $bin;
+
+ /**
+ * Prefix for all keys in the storage that belong to this site.
+ *
+ * @var string
+ */
+ protected $sitePrefix;
+
+ /**
+ * Prefix for all keys in this cache bin.
+ *
+ * Includes the site-specific prefix in $sitePrefix.
+ *
+ * @var string
+ */
+ protected $binPrefix;
+
+ /**
+ * Prefix for keys holding invalidation cache tags.
+ *
+ * Includes the site-specific prefix in $sitePrefix.
+ *
+ * @var string
+ */
+ protected $invalidationsTagsPrefix;
+
+ /**
+ * Prefix for keys holding invalidation cache tags.
+ *
+ * Includes the site-specific prefix in $sitePrefix.
+ *
+ * @var string
+ */
+ protected $deletionsTagsPrefix;
+
+ /**
+ * A static cache of all tags checked during the request.
+ *
+ * @var array
+ */
+ protected static $tagCache = array('deletions' => array(), 'invalidations' => array());
+
+ /**
+ * Constructs a new ApcuBackend instance.
+ *
+ * @param string $bin
+ * The name of the cache bin.
+ * @param string $site_prefix
+ * The prefix to use for all keys in the storage that belong to this site.
+ */
+ public function __construct($bin, $site_prefix) {
+ $this->bin = $bin;
+ $this->sitePrefix = $site_prefix;
+ $this->binPrefix = $this->sitePrefix . '::' . $this->bin . '::';
+ $this->invalidationsTagsPrefix = $this->sitePrefix . '::itags::';
+ $this->deletionsTagsPrefix = $this->sitePrefix . '::dtags::';
+ }
+
+ /**
+ * Prepends the APC user variable prefix for this bin to a cache item ID.
+ *
+ * @param string $cid
+ * The cache item ID to prefix.
+ *
+ * @return string
+ * The APCu key for the cache item ID.
+ */
+ protected function getApcuKey($cid) {
+ return $this->binPrefix . $cid;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function get($cid, $allow_invalid = FALSE) {
+ $cache = apc_fetch($this->getApcuKey($cid));
+ return $this->prepareItem($cache, $allow_invalid);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getMultiple(&$cids, $allow_invalid = FALSE) {
+ // Translate the requested cache item IDs to APCu keys.
+ $map = array();
+ foreach ($cids as $cid) {
+ $map[$this->getApcuKey($cid)] = $cid;
+ }
+
+ $result = apc_fetch(array_keys($map));
+ $cache = array();
+ foreach ($result as $key => $item) {
+ $item = $this->prepareItem($item, $allow_invalid);
+ if ($item) {
+ $cache[$map[$key]] = $item;
+ }
+ }
+ unset($result);
+
+ $cids = array_diff($cids, array_keys($cache));
+ return $cache;
+ }
+
+ /**
+ * Returns all cached items, optionally limited by a cache ID prefix.
+ *
+ * APCu is a memory cache, shared across all server processes. To prevent
+ * cache item clashes with other applications/installations, every cache item
+ * is prefixed with a unique string for this site. Therefore, functions like
+ * apc_clear_cache() cannot be used, and instead, a list of all cache items
+ * belonging to this application need to be retrieved through this method
+ * instead.
+ *
+ * @param string $prefix
+ * (optional) A cache ID prefix to limit the result to.
+ *
+ * @return \APCIterator
+ * An APCIterator containing matched items.
+ */
+ protected function getAll($prefix = '') {
+ return new \APCIterator('user', '/^' . preg_quote($this->getApcuKey($prefix), '/') . '/');
+ }
+
+ /**
+ * Prepares a cached item.
+ *
+ * Checks that the item is either permanent or did not expire.
+ *
+ * @param \stdClass $cache
+ * An item loaded from cache_get() or cache_get_multiple().
+ * @param bool $allow_invalid
+ * If TRUE, a cache item may be returned even if it is expired or has been
+ * invalidated. See ::get().
+ *
+ * @return mixed
+ * The cache item or FALSE if the item expired.
+ */
+ protected function prepareItem($cache, $allow_invalid) {
+ if (!isset($cache->data)) {
+ return FALSE;
+ }
+
+ $cache->tags = $cache->tags ? explode(' ', $cache->tags) : array();
+ $checksum = $this->checksumTags($cache->tags);
+
+ // Check if deleteTags() has been called with any of the entry's tags.
+ if ($cache->checksum_deletions != $checksum['deletions']) {
+ return FALSE;
+ }
+
+ // Check expire time.
+ $cache->valid = $cache->expire == Cache::PERMANENT || $cache->expire >= REQUEST_TIME;
+
+ // Check if invalidateTags() has been called with any of the entry's tags.
+ if ($cache->checksum_invalidations != $checksum['invalidations']) {
+ $cache->valid = FALSE;
+ }
+
+ if (!$allow_invalid && !$cache->valid) {
+ return FALSE;
+ }
+
+ return $cache;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function set($cid, $data, $expire = CacheBackendInterface::CACHE_PERMANENT, array $tags = array()) {
+ $cache = new \stdClass();
+ $cache->cid = $cid;
+ $cache->created = REQUEST_TIME;
+ $cache->expire = $expire;
+ $cache->tags = implode(' ', $this->flattenTags($tags));
+ $checksum = $this->checksumTags($tags);
+ $cache->checksum_invalidations = $checksum['invalidations'];
+ $cache->checksum_deletions = $checksum['deletions'];
+ // APC serializes/unserializes any structure itself.
+ $cache->serialized = 0;
+ $cache->data = $data;
+
+ // apc_store()'s $ttl argument can be omitted but also set to 0 (zero),
+ // in which case the value will persist until it's removed from the cache or
+ // until the next cache clear, restart, etc. This is what we want to do
+ // when $expire equals CacheBackendInterface::CACHE_PERMANENT.
+ if ($expire === CacheBackendInterface::CACHE_PERMANENT) {
+ $expire = 0;
+ }
+ apc_store($this->getApcuKey($cid), $cache, $expire);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function setMultiple(array $items = array()) {
+ foreach ($items as $cid => $item) {
+ $this->set($cid, $item['data'], isset($item['expire']) ? $item['expire'] : CacheBackendInterface::CACHE_PERMANENT, isset($item['tags']) ? $item['tags'] : array());
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function delete($cid) {
+ apc_delete($this->getApcuKey($cid));
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function deleteMultiple(array $cids) {
+ apc_delete(array_map(array($this, 'getApcuKey'), $cids));
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function deleteAll() {
+ apc_delete(new \APCIterator('user', '/^' . preg_quote($this->binPrefix, '/') . '/'));
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function garbageCollection() {
+ // Any call to apc_fetch() causes APC to expunge expired items.
+ apc_fetch('');
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function removeBin() {
+ apc_delete(new \APCIterator('user', '/^' . preg_quote($this->binPrefix, '/') . '/'));
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function isEmpty() {
+ return $this->getAll()->getTotalCount() === 0;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function invalidate($cid) {
+ $this->invalidateMultiple(array($cid));
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function invalidateMultiple(array $cids) {
+ foreach ($this->getMultiple($cids) as $cache) {
+ $this->set($cache->cid, $cache, REQUEST_TIME - 1);
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function invalidateAll() {
+ foreach ($this->getAll() as $data) {
+ $cid = str_replace($this->binPrefix, '', $data['key']);
+ $this->set($cid, $data['value'], REQUEST_TIME - 1);
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function deleteTags(array $tags) {
+ foreach ($this->flattenTags($tags) as $tag) {
+ apc_inc($this->deletionsTagsPrefix . $tag, 1, $success);
+ if (!$success) {
+ apc_store($this->deletionsTagsPrefix . $tag, 1);
+ }
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function invalidateTags(array $tags) {
+ foreach ($this->flattenTags($tags) as $tag) {
+ apc_inc($this->invalidationsTagsPrefix . $tag, 1, $success);
+ if (!$success) {
+ apc_store($this->invalidationsTagsPrefix . $tag, 1);
+ }
+ }
+ }
+
+ /**
+ * Flattens a tags array into a numeric array suitable for string storage.
+ *
+ * @param array $tags
+ * Associative array of tags to flatten.
+ *
+ * @return array
+ * Indexed array of flattened tag identifiers.
+ */
+ protected function flattenTags(array $tags) {
+ if (isset($tags[0])) {
+ return $tags;
+ }
+
+ $flat_tags = array();
+ foreach ($tags as $namespace => $values) {
+ if (is_array($values)) {
+ foreach ($values as $value) {
+ $flat_tags[] = "$namespace:$value";
+ }
+ }
+ else {
+ $flat_tags[] = "$namespace:$values";
+ }
+ }
+ return $flat_tags;
+ }
+
+ /**
+ * Returns the sum total of validations for a given set of tags.
+ *
+ * @param array $tags
+ * Associative array of tags.
+ *
+ * @return int
+ * Sum of all invalidations.
+ */
+ protected function checksumTags(array $tags) {
+ $checksum = array('invalidations' => 0, 'deletions' => 0);
+ $query_tags = array('invalidations' => array(), 'deletions' => array());
+
+ foreach ($this->flattenTags($tags) as $tag) {
+ foreach (array('deletions', 'invalidations') as $type) {
+ if (isset(static::$tagCache[$type][$tag])) {
+ $checksum[$type] += static::$tagCache[$type][$tag];
+ }
+ else {
+ $query_tags[$type][] = $this->{$type . 'TagsPrefix'} . $tag;
+ }
+ }
+ }
+
+ foreach (array('deletions', 'invalidations') as $type) {
+ if ($query_tags[$type]) {
+ $result = apc_fetch($query_tags[$type]);
+ static::$tagCache[$type] = array_merge(static::$tagCache[$type], $result);
+ $checksum[$type] += array_sum($result);
+ }
+ }
+
+ return $checksum;
+ }
+
+}
diff --git a/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php b/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php
new file mode 100644
index 0000000000000000000000000000000000000000..341203c4a88c5098d89ef4e3ac85c9f9c8c813e9
--- /dev/null
+++ b/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php
@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Cache\ApcuBackendFactory.
+ */
+
+namespace Drupal\Core\Cache;
+
+use \Drupal\Component\Utility\Crypt;
+
+class ApcuBackendFactory implements CacheFactoryInterface {
+
+ /**
+ * The site prefix string.
+ *
+ * @var string
+ */
+ protected $sitePrefix;
+
+ /**
+ * Constructs an ApcuBackendFactory object.
+ */
+ public function __construct() {
+ $this->sitePrefix = Crypt::hashBase64(DRUPAL_ROOT . '/' . conf_path());
+ }
+
+ /**
+ * Gets ApcuBackend for the specified cache bin.
+ *
+ * @param $bin
+ * The cache bin for which the object is created.
+ *
+ * @return \Drupal\Core\Cache\ApcuBackend
+ * The cache backend object for the specified cache bin.
+ */
+ public function get($bin) {
+ return new ApcuBackend($bin, $this->sitePrefix);
+ }
+
+}
diff --git a/core/modules/system/lib/Drupal/system/Tests/Cache/ApcuBackendUnitTest.php b/core/modules/system/lib/Drupal/system/Tests/Cache/ApcuBackendUnitTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..2aae6639c750422e6a7b0f5a1df03ce5795cb97f
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/Cache/ApcuBackendUnitTest.php
@@ -0,0 +1,52 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Cache\ApcuBackendUnitTest.
+ */
+
+namespace Drupal\system\Tests\Cache;
+
+use Drupal\Core\Cache\ApcuBackend;
+
+/**
+ * Tests the APCu cache backend.
+ */
+class ApcuBackendUnitTest extends GenericCacheBackendUnitTestBase {
+
+ public static function getInfo() {
+ return array(
+ 'name' => 'APCu cache backend',
+ 'description' => 'Tests the APCu cache backend.',
+ 'group' => 'Cache',
+ );
+ }
+
+ protected function checkRequirements() {
+ $requirements = parent::checkRequirements();
+ if (!extension_loaded('apc')) {
+ $requirements[] = 'APC extension not found.';
+ }
+ else {
+ if (version_compare(phpversion('apc'), '3.1.1', '<')) {
+ $requirements[] = 'APC extension must be newer than 3.1.1 for APCIterator support.';
+ }
+ if (PHP_SAPI === 'cli' && !ini_get('apc.enable_cli')) {
+ $requirements[] = 'apc.enable_cli must be enabled to run this test.';
+ }
+ }
+ return $requirements;
+ }
+
+ protected function createCacheBackend($bin) {
+ $this->backend = new ApcuBackend($bin, $this->databasePrefix);
+ return $this->backend;
+ }
+
+ public function tearDown() {
+ $this->backend->removeBin();
+ parent::tearDown();
+ $this->backend = NULL;
+ }
+
+}