From 426e9c79ac1f2e40ae7841319f71266e07a842cf Mon Sep 17 00:00:00 2001
From: Sam Hemelryk <sam@moodle.com>
Date: Mon, 26 Aug 2013 09:15:57 +1200
Subject: [PATCH] MDL-41106 cache: several fixes for the session cache.

This issue makes several fixes for the session loader and the session store.
 * maxsize argument now works for session caches.
 * fixed performance hole when interation occurs frequently.
 * fixed cache purge bug occuring when multiple caches are defined before being used.
 * improved lastaccess handling.

Big thanks to Marina who contributed the following commits:
 * Always make sure the elements in cache are sorted so we need to remove only elements in the beginning of array
 * Remove expired elements from session store to free memory
 * Minor bug fixes
---
 cache/classes/loaders.php    | 333 ++++++++++++++++++++---------------
 cache/stores/session/lib.php |  68 ++++++-
 cache/tests/cache_test.php   |  91 +++++++++-
 cache/tests/fixtures/lib.php |  18 ++
 4 files changed, 359 insertions(+), 151 deletions(-)

diff --git a/cache/classes/loaders.php b/cache/classes/loaders.php
index da8fe6758bf..6de94e299b3 100644
--- a/cache/classes/loaders.php
+++ b/cache/classes/loaders.php
@@ -271,7 +271,7 @@ class cache implements cache_loader {
      *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
      * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
      * @return mixed|false The data from the cache or false if the key did not exist within the cache.
-     * @throws moodle_exception
+     * @throws coding_exception
      */
     public function get($key, $strictness = IGNORE_MISSING) {
         // 1. Parse the key.
@@ -329,7 +329,7 @@ class cache implements cache_loader {
         }
         // 5. Validate strictness.
         if ($strictness === MUST_EXIST && $result === false) {
-            throw new moodle_exception('Requested key did not exist in any cache stores and could not be loaded.');
+            throw new coding_exception('Requested key did not exist in any cache stores and could not be loaded.');
         }
         // 6. Set it to the store if we got it from the loader/datasource.
         if ($setaftervalidation) {
@@ -363,7 +363,7 @@ class cache implements cache_loader {
      * @return array An array of key value pairs for the items that could be retrieved from the cache.
      *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
      *      Otherwise any key that did not exist will have a data value of false within the results.
-     * @throws moodle_exception
+     * @throws coding_exception
      */
     public function get_many(array $keys, $strictness = IGNORE_MISSING) {
 
@@ -420,7 +420,7 @@ class cache implements cache_loader {
             $missingkeys = array();
             foreach ($result as $key => $value) {
                 if ($value === false) {
-                    $missingkeys[] = ($usingloader) ? $key : $parsedkeys[$key];
+                    $missingkeys[] = $parsedkeys[$key];
                 }
             }
             if (!empty($missingkeys)) {
@@ -430,11 +430,9 @@ class cache implements cache_loader {
                     $resultmissing = $this->datasource->load_many_for_cache($missingkeys);
                 }
                 foreach ($resultmissing as $key => $value) {
-                    $pkey = ($usingloader) ? $key : $keysparsed[$key];
-                    $realkey = ($usingloader) ? $parsedkeys[$key] : $key;
-                    $result[$pkey] = $value;
+                    $result[$keysparsed[$key]] = $value;
                     if ($value !== false) {
-                        $this->set($realkey, $value);
+                        $this->set($key, $value);
                     }
                 }
                 unset($resultmissing);
@@ -453,7 +451,7 @@ class cache implements cache_loader {
         if ($strictness === MUST_EXIST) {
             foreach ($keys as $key) {
                 if (!array_key_exists($key, $fullresult)) {
-                    throw new moodle_exception('Not all the requested keys existed within the cache stores.');
+                    throw new coding_exception('Not all the requested keys existed within the cache stores.');
                 }
             }
         }
@@ -483,6 +481,11 @@ class cache implements cache_loader {
         if ($this->perfdebug) {
             cache_helper::record_cache_set($this->storetype, $this->definition->get_id());
         }
+        if ($this->loader !== false) {
+            // We have a loader available set it there as well.
+            // We have to let the loader do its own parsing of data as it may be unique.
+            $this->loader->set($key, $data);
+        }
         if (is_object($data) && $data instanceof cacheable_object) {
             $data = new cache_cached_object($data);
         } else if (!is_scalar($data)) {
@@ -506,6 +509,7 @@ class cache implements cache_loader {
      * Removes references where required.
      *
      * @param stdClass|array $data
+     * @return mixed What ever was put in but without any references.
      */
     protected function unref($data) {
         if ($this->definition->uses_simple_data()) {
@@ -593,6 +597,11 @@ class cache implements cache_loader {
      *      ... if they care that is.
      */
     public function set_many(array $keyvaluearray) {
+        if ($this->loader !== false) {
+            // We have a loader available set it there as well.
+            // We have to let the loader do its own parsing of data as it may be unique.
+            $this->loader->set_many($keyvaluearray);
+        }
         $data = array();
         $simulatettl = $this->has_a_ttl() && !$this->store_supports_native_ttl();
         $usepersistcache = $this->is_using_persist_cache();
@@ -858,7 +867,7 @@ class cache implements cache_loader {
      * Returns the loader associated with this instance.
      *
      * @since 2.4.4
-     * @return cache_loader|false
+     * @return cache|false
      */
     protected function get_loader() {
         return $this->loader;
@@ -1340,7 +1349,6 @@ class cache_application extends cache implements cache_loader_with_locking {
      * @param string|int $key The key for the data being requested.
      * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
      * @return mixed|false The data from the cache or false if the key did not exist within the cache.
-     * @throws moodle_exception
      */
     public function get($key, $strictness = IGNORE_MISSING) {
         if ($this->requirelockingread && $this->check_lock_state($key) === false) {
@@ -1364,7 +1372,7 @@ class cache_application extends cache implements cache_loader_with_locking {
      * @return array An array of key value pairs for the items that could be retrieved from the cache.
      *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
      *      Otherwise any key that did not exist will have a data value of false within the results.
-     * @throws moodle_exception
+     * @throws coding_exception
      */
     public function get_many(array $keys, $strictness = IGNORE_MISSING) {
         if ($this->requirelockingread) {
@@ -1458,6 +1466,7 @@ class cache_application extends cache implements cache_loader_with_locking {
  * @todo we should support locking in the session as well. Should be pretty simple to set up.
  *
  * @internal don't use me directly.
+ * @method cache_store|cache_is_searchable get_store() Returns the cache store which must implement both cache_is_searchable.
  *
  * @package    core
  * @category   cache
@@ -1494,6 +1503,11 @@ class cache_session extends cache {
      */
     const KEY_PREFIX = 'sess_';
 
+    /**
+     * This is the key used to track last access.
+     */
+    const LASTACCESS = '__lastaccess__';
+
     /**
      * Override the cache::construct method.
      *
@@ -1507,12 +1521,15 @@ class cache_session extends cache {
      * @param cache_definition $definition
      * @param cache_store $store
      * @param cache_loader|cache_data_source $loader
-     * @return void
      */
     public function __construct(cache_definition $definition, cache_store $store, $loader = null) {
         // First up copy the loadeduserid to the current user id.
         $this->currentuserid = self::$loadeduserid;
         parent::__construct($definition, $store, $loader);
+
+        // This will trigger check tracked user. If this gets removed a call to that will need to be added here in its place.
+        $this->set(self::LASTACCESS, cache::now());
+
         if ($definition->has_invalidation_events()) {
             $lastinvalidation = $this->get('lastsessioninvalidation');
             if ($lastinvalidation === false) {
@@ -1561,6 +1578,21 @@ class cache_session extends cache {
         }
     }
 
+    /**
+     * Sets the session id for the loader.
+     */
+    protected function set_session_id() {
+        $this->sessionid = preg_replace('#[^a-zA-Z0-9_]#', '_', session_id());
+    }
+
+    /**
+     * Returns the prefix used for all keys.
+     * @return string
+     */
+    protected function get_key_prefix() {
+        return 'u'.$this->currentuserid.'_'.$this->sessionid;
+    }
+
     /**
      * Parses the key turning it into a string (or array is required) suitable to be passed to the cache store.
      *
@@ -1573,17 +1605,18 @@ class cache_session extends cache {
      * @return string|array String unless the store supports multi-identifiers in which case an array if returned.
      */
     protected function parse_key($key) {
-        if ($key === 'lastaccess') {
-            $key = '__lastaccess__';
+        $prefix = $this->get_key_prefix();
+        if ($key === self::LASTACCESS) {
+            return $key.$prefix;
         }
-        return 'sess_'.parent::parse_key($key);
+        return $prefix.'_'.parent::parse_key($key);
     }
 
     /**
      * Check that this cache instance is tracking the current user.
      */
     protected function check_tracked_user() {
-        if (isset($_SESSION['USER']->id)) {
+        if (isset($_SESSION['USER']->id) && $_SESSION['USER']->id !== null) {
             // Get the id of the current user.
             $new = $_SESSION['USER']->id;
         } else {
@@ -1597,55 +1630,25 @@ class cache_session extends cache {
                 // This way we don't bloat the session.
                 $this->purge();
                 // Update the session id just in case!
-                $this->sessionid = session_id();
+                $this->set_session_id();
             }
             self::$loadeduserid = $new;
             $this->currentuserid = $new;
         } else if ($new !== $this->currentuserid) {
             // The current user matches the loaded user but not the user last used by this cache.
-            $this->purge();
+            $this->purge_current_user();
             $this->currentuserid = $new;
             // Update the session id just in case!
-            $this->sessionid = session_id();
+            $this->set_session_id();
         }
     }
 
     /**
-     * Gets the session data.
-     *
-     * @param bool $force If true the session data will be loaded from the store again.
-     * @return array An array of session data.
+     * Purges the session cache of all data belonging to the current user.
      */
-    protected function get_session_data($force = false) {
-        if ($this->sessionid === null) {
-            $this->sessionid = session_id();
-        }
-        if (is_array($this->session) && !$force) {
-            return $this->session;
-        }
-        $session = parent::get($this->sessionid);
-        if ($session === false) {
-            $session = array();
-        }
-        // We have to write here to ensure that the lastaccess time is recorded.
-        // And also in order to ensure the session entry exists as when we save it on __destruct
-        // $CFG is likely to have already been destroyed.
-        $this->save_session($session);
-        return $this->session;
-    }
-
-    /**
-     * Saves the session data.
-     *
-     * This function also updates the last access time.
-     *
-     * @param array $session
-     * @return bool
-     */
-    protected function save_session(array $session) {
-        $session['lastaccess'] = time();
-        $this->session = $session;
-        return parent::set($this->sessionid, $this->session);
+    public function purge_current_user() {
+        $keys = $this->get_store()->find_all($this->get_key_prefix());
+        $this->get_store()->delete_many($keys);
     }
 
     /**
@@ -1656,7 +1659,7 @@ class cache_session extends cache {
      *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
      * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
      * @return mixed|false The data from the cache or false if the key did not exist within the cache.
-     * @throws moodle_exception
+     * @throws coding_exception
      */
     public function get($key, $strictness = IGNORE_MISSING) {
         // Check the tracked user.
@@ -1664,10 +1667,8 @@ class cache_session extends cache {
         // 2. Parse the key.
         $parsedkey = $this->parse_key($key);
         // 3. Get it from the store.
-        $result = false;
-        $session = $this->get_session_data();
-        if (array_key_exists($parsedkey, $session)) {
-            $result = $session[$parsedkey];
+        $result = $this->get_store()->get($parsedkey);
+        if ($result !== false) {
             if ($result instanceof cache_ttl_wrapper) {
                 if ($result->has_expired()) {
                     $this->get_store()->delete($parsedkey);
@@ -1681,10 +1682,9 @@ class cache_session extends cache {
             }
         }
         // 4. Load if from the loader/datasource if we don't already have it.
-        $setaftervalidation = false;
         if ($result === false) {
             if ($this->perfdebug) {
-                cache_helper::record_cache_miss('**static session**', $this->get_definition()->get_id());
+                cache_helper::record_cache_miss($this->storetype, $this->get_definition()->get_id());
             }
             if ($this->get_loader() !== false) {
                 // We must pass the original (unparsed) key to the next loader in the chain.
@@ -1694,19 +1694,18 @@ class cache_session extends cache {
             } else if ($this->get_datasource() !== false) {
                 $result = $this->get_datasource()->load_for_cache($key);
             }
-            $setaftervalidation = ($result !== false);
+            // 5. Set it to the store if we got it from the loader/datasource.
+            if ($result !== false) {
+                $this->set($key, $result);
+            }
         } else if ($this->perfdebug) {
-            cache_helper::record_cache_hit('**static session**', $this->get_definition()->get_id());
+            cache_helper::record_cache_hit($this->storetype, $this->get_definition()->get_id());
         }
         // 5. Validate strictness.
         if ($strictness === MUST_EXIST && $result === false) {
-            throw new moodle_exception('Requested key did not exist in any cache stores and could not be loaded.');
+            throw new coding_exception('Requested key did not exist in any cache stores and could not be loaded.');
         }
-        // 6. Set it to the store if we got it from the loader/datasource.
-        if ($setaftervalidation) {
-            $this->set($key, $result);
-        }
-        // 7. Make sure we don't pass back anything that could be a reference.
+        // 6. Make sure we don't pass back anything that could be a reference.
         //    We don't want people modifying the data in the cache.
         if (!is_scalar($result)) {
             // If data is an object it will be a reference.
@@ -1737,8 +1736,14 @@ class cache_session extends cache {
      */
     public function set($key, $data) {
         $this->check_tracked_user();
+        $loader = $this->get_loader();
+        if ($loader !== false) {
+            // We have a loader available set it there as well.
+            // We have to let the loader do its own parsing of data as it may be unique.
+            $loader->set($key, $data);
+        }
         if ($this->perfdebug) {
-            cache_helper::record_cache_set('**static session**', $this->get_definition()->get_id());
+            cache_helper::record_cache_set($this->storetype, $this->get_definition()->get_id());
         }
         if (is_object($data) && $data instanceof cacheable_object) {
             $data = new cache_cached_object($data);
@@ -1750,12 +1755,10 @@ class cache_session extends cache {
             $data = $this->unref($data);
         }
         // We dont' support native TTL here as we consolidate data for sessions.
-        if ($this->has_a_ttl()) {
+        if ($this->has_a_ttl() && !$this->store_supports_native_ttl()) {
             $data = new cache_ttl_wrapper($data, $this->get_definition()->get_ttl());
         }
-        $session = $this->get_session_data();
-        $session[$this->parse_key($key)] = $data;
-        return $this->save_session($session);
+        return $this->get_store()->set($this->parse_key($key), $data);
     }
 
     /**
@@ -1767,15 +1770,12 @@ class cache_session extends cache {
      * @return bool True of success, false otherwise.
      */
     public function delete($key, $recurse = true) {
-        $this->check_tracked_user();
         $parsedkey = $this->parse_key($key);
         if ($recurse && $this->get_loader() !== false) {
             // Delete from the bottom of the stack first.
             $this->get_loader()->delete($key, $recurse);
         }
-        $session = $this->get_session_data();
-        unset($session[$parsedkey]);
-        return $this->save_session($session);
+        return $this->get_store()->delete($parsedkey);
     }
 
     /**
@@ -1794,15 +1794,72 @@ class cache_session extends cache {
      * @return array An array of key value pairs for the items that could be retrieved from the cache.
      *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
      *      Otherwise any key that did not exist will have a data value of false within the results.
-     * @throws moodle_exception
+     * @throws coding_exception
      */
     public function get_many(array $keys, $strictness = IGNORE_MISSING) {
         $this->check_tracked_user();
-        $return = array();
+        $parsedkeys = array();
+        $keymap = array();
         foreach ($keys as $key) {
-            $return[$key] = $this->get($key, $strictness);
+            $parsedkey = $this->parse_key($key);
+            $parsedkeys[$key] = $parsedkey;
+            $keymap[$parsedkey] = $key;
         }
+        $result = $this->get_store()->get_many($parsedkeys);
+        $return = array();
+        $missingkeys = array();
+        $hasmissingkeys = false;
+        foreach ($result as $parsedkey => $value) {
+            $key = $keymap[$parsedkey];
+            if ($value instanceof cache_ttl_wrapper) {
+                /* @var cache_ttl_wrapper $value */
+                if ($value->has_expired()) {
+                    $this->delete($keymap[$parsedkey]);
+                    $value = false;
+                } else {
+                    $value = $value->data;
+                }
+            }
+            if ($value instanceof cache_cached_object) {
+                /* @var cache_cached_object $value */
+                $value = $value->restore_object();
+            }
+            $return[$key] = $value;
+            if ($value === false) {
+                $hasmissingkeys = true;
+                $missingkeys[$parsedkey] = $key;
+            }
+        }
+        if ($hasmissingkeys) {
+            // We've got missing keys - we've got to check any loaders or data sources.
+            $loader = $this->get_loader();
+            $datasource = $this->get_datasource();
+            if ($loader !== false) {
+                foreach ($loader->get_many($missingkeys) as $key => $value) {
+                    if ($value !== false) {
+                        $return[$key] = $value;
+                        unset($missingkeys[$parsedkeys[$key]]);
+                    }
+                }
+            }
+            $hasmissingkeys = count($missingkeys) > 0;
+            if ($datasource !== false && $hasmissingkeys) {
+                // We're still missing keys but we've got a datasource.
+                foreach ($datasource->load_many_for_cache($missingkeys) as $key => $value) {
+                    if ($value !== false) {
+                        $return[$key] = $value;
+                        unset($missingkeys[$parsedkeys[$key]]);
+                    }
+                }
+                $hasmissingkeys = count($missingkeys) > 0;
+            }
+        }
+        if ($hasmissingkeys && $strictness === MUST_EXIST) {
+            throw new coding_exception('Requested key did not exist in any cache stores and could not be loaded.');
+        }
+
         return $return;
+
     }
 
     /**
@@ -1814,18 +1871,12 @@ class cache_session extends cache {
      * @return int The number of items successfully deleted.
      */
     public function delete_many(array $keys, $recurse = true) {
-        $this->check_tracked_user();
         $parsedkeys = array_map(array($this, 'parse_key'), $keys);
         if ($recurse && $this->get_loader() !== false) {
             // Delete from the bottom of the stack first.
             $this->get_loader()->delete_many($keys, $recurse);
         }
-        $session = $this->get_session_data();
-        foreach ($parsedkeys as $parsedkey) {
-            unset($session[$parsedkey]);
-        }
-        $this->save_session($session);
-        return count($keys);
+        return $this->get_store()->delete_many($parsedkeys);
     }
 
     /**
@@ -1853,8 +1904,15 @@ class cache_session extends cache {
      */
     public function set_many(array $keyvaluearray) {
         $this->check_tracked_user();
-        $session = $this->get_session_data();
-        $simulatettl = $this->has_a_ttl();
+        $loader = $this->get_loader();
+        if ($loader !== false) {
+            // We have a loader available set it there as well.
+            // We have to let the loader do its own parsing of data as it may be unique.
+            $loader->set_many($keyvaluearray);
+        }
+        $data = array();
+        $definitionid = $this->get_definition()->get_ttl();
+        $simulatettl = $this->has_a_ttl() && !$this->store_supports_native_ttl();
         foreach ($keyvaluearray as $key => $value) {
             if (is_object($value) && $value instanceof cacheable_object) {
                 $value = new cache_cached_object($value);
@@ -1866,16 +1924,17 @@ class cache_session extends cache {
                 $value = $this->unref($value);
             }
             if ($simulatettl) {
-                $value = new cache_ttl_wrapper($value, $this->get_definition()->get_ttl());
+                $value = new cache_ttl_wrapper($value, $definitionid);
             }
-            $parsedkey = $this->parse_key($key);
-            $session[$parsedkey] = $value;
+            $data[$key] = array(
+                'key' => $this->parse_key($key),
+                'value' => $value
+            );
         }
         if ($this->perfdebug) {
-            cache_helper::record_cache_set($this->storetype, $this->get_definition()->get_id());
+            cache_helper::record_cache_set($this->storetype, $definitionid);
         }
-        $this->save_session($session);
-        return count($keyvaluearray);
+        return $this->get_store()->set_many($data);
     }
 
     /**
@@ -1884,13 +1943,9 @@ class cache_session extends cache {
      * @return bool True on success, false otherwise
      */
     public function purge() {
-        // 1. Purge the session object.
-        $this->session = array();
-        // 2. Delete the record for this users session from the store.
-        $this->get_store()->delete($this->sessionid);
-        // 3. Optionally purge any stacked loaders in the same way.
+        $this->get_store()->purge();
         if ($this->get_loader()) {
-            $this->get_loader()->delete($this->sessionid);
+            $this->get_loader()->purge();
         }
         return true;
     }
@@ -1919,21 +1974,27 @@ class cache_session extends cache {
     public function has($key, $tryloadifpossible = false) {
         $this->check_tracked_user();
         $parsedkey = $this->parse_key($key);
-        $session = $this->get_session_data();
-        $has = false;
-        if ($this->has_a_ttl()) {
+        $store = $this->get_store();
+        if ($this->has_a_ttl() && !$this->store_supports_native_ttl()) {
             // The data has a TTL and the store doesn't support it natively.
             // We must fetch the data and expect a ttl wrapper.
-            if (array_key_exists($parsedkey, $session)) {
-                $data = $session[$parsedkey];
-                $has = ($data instanceof cache_ttl_wrapper && !$data->has_expired());
-            }
+            $data = $store->get($parsedkey);
+            $has = ($data instanceof cache_ttl_wrapper && !$data->has_expired());
+        } else if (!$this->store_supports_key_awareness()) {
+            // The store doesn't support key awareness, get the data and check it manually... puke.
+            // Either no TTL is set of the store supports its handling natively.
+            $data = $store->get($parsedkey);
+            $has = ($data !== false);
         } else {
-            $has = array_key_exists($parsedkey, $session);
+            // The store supports key awareness, this is easy!
+            // Either no TTL is set of the store supports its handling natively.
+            /* @var cache_store|cache_is_key_aware $store */
+            $has = $store->has($parsedkey);
         }
         if (!$has && $tryloadifpossible) {
+            $result = null;
             if ($this->get_loader() !== false) {
-                $result = $this->get_loader()->get($key);
+                $result = $this->get_loader()->get($parsedkey);
             } else if ($this->get_datasource() !== null) {
                 $result = $this->get_datasource()->load_for_cache($key);
             }
@@ -1960,25 +2021,18 @@ class cache_session extends cache {
      */
     public function has_all(array $keys) {
         $this->check_tracked_user();
-        $session = $this->get_session_data();
-        foreach ($keys as $key) {
-            $has = false;
-            $parsedkey = $this->parse_key($key);
-            if ($this->has_a_ttl()) {
-                // The data has a TTL and the store doesn't support it natively.
-                // We must fetch the data and expect a ttl wrapper.
-                if (array_key_exists($parsedkey, $session)) {
-                    $data = $session[$parsedkey];
-                    $has = ($data instanceof cache_ttl_wrapper && !$data->has_expired());
+        if (($this->has_a_ttl() && !$this->store_supports_native_ttl()) || !$this->store_supports_key_awareness()) {
+            foreach ($keys as $key) {
+                if (!$this->has($key)) {
+                    return false;
                 }
-            } else {
-                $has = array_key_exists($parsedkey, $session);
-            }
-            if (!$has) {
-                return false;
             }
+            return true;
         }
-        return true;
+        // The cache must be key aware and if support native ttl if it a ttl is set.
+        /* @var cache_store|cache_is_key_aware $store */
+        $store = $this->get_store();
+        return $store->has_all(array_map(array($this, 'parse_key'), $keys));
     }
 
     /**
@@ -1995,26 +2049,17 @@ class cache_session extends cache {
      * @return bool True if the cache has at least one of the given keys
      */
     public function has_any(array $keys) {
-        $this->check_tracked_user();
-        $session = $this->get_session_data();
-        foreach ($keys as $key) {
-            $has = false;
-            $parsedkey = $this->parse_key($key);
-            if ($this->has_a_ttl()) {
-                // The data has a TTL and the store doesn't support it natively.
-                // We must fetch the data and expect a ttl wrapper.
-                if (array_key_exists($parsedkey, $session)) {
-                    $data = $session[$parsedkey];
-                    $has = ($data instanceof cache_ttl_wrapper && !$data->has_expired());
+        if (($this->has_a_ttl() && !$this->store_supports_native_ttl()) || !$this->store_supports_key_awareness()) {
+            foreach ($keys as $key) {
+                if ($this->has($key)) {
+                    return true;
                 }
-            } else {
-                $has = array_key_exists($parsedkey, $session);
-            }
-            if ($has) {
-                return true;
             }
+            return false;
         }
-        return false;
+        /* @var cache_store|cache_is_key_aware $store */
+        $store = $this->get_store();
+        return $store->has_any(array_map(array($this, 'parse_key'), $keys));
     }
 
     /**
diff --git a/cache/stores/session/lib.php b/cache/stores/session/lib.php
index 801dfcb3ee8..d1f735d3b59 100644
--- a/cache/stores/session/lib.php
+++ b/cache/stores/session/lib.php
@@ -190,8 +190,9 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      */
     public function initialise(cache_definition $definition) {
         $this->storeid = $definition->generate_definition_hash();
-        $this->store = &self::register_store_id($definition->get_id());
+        $this->store = &self::register_store_id($this->name.'-'.$definition->get_id());
         $this->ttl = $definition->get_ttl();
+        $this->check_ttl();
     }
 
     /**
@@ -219,10 +220,13 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      */
     public function get($key) {
         if (isset($this->store[$key])) {
-            if ($this->ttl == 0) {
+            if ($this->ttl === 0) {
                 return $this->store[$key][0];
             } else if ($this->store[$key][1] >= (cache::now() - $this->ttl)) {
                 return $this->store[$key][0];
+            } else {
+                // Element is present but has expired.
+                $this->check_ttl();
             }
         }
         return false;
@@ -239,10 +243,12 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      */
     public function get_many($keys) {
         $return = array();
+        $maxtime = 0;
         if ($this->ttl != 0) {
             $maxtime = cache::now() - $this->ttl;
         }
 
+        $hasexpiredelements = false;
         foreach ($keys as $key) {
             $return[$key] = false;
             if (isset($this->store[$key])) {
@@ -250,9 +256,15 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
                     $return[$key] = $this->store[$key][0];
                 } else if ($this->store[$key][1] >= $maxtime) {
                     $return[$key] = $this->store[$key][0];
+                } else {
+                    $hasexpiredelements = true;
                 }
             }
         }
+        if ($hasexpiredelements) {
+            // There are some elements that are present but have expired.
+            $this->check_ttl();
+        }
         return $return;
     }
 
@@ -264,8 +276,8 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      * @return bool True if the operation was a success false otherwise.
      */
     public function set($key, $data) {
-        if ($this->ttl == 0) {
-            $this->store[$key][0] = $data;
+        if ($this->ttl === 0) {
+            $this->store[$key] = array($data, 0);
         } else {
             $this->store[$key] = array($data, cache::now());
         }
@@ -283,8 +295,14 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
     public function set_many(array $keyvaluearray) {
         $count = 0;
         foreach ($keyvaluearray as $pair) {
-            $this->set($pair['key'], $pair['value']);
+            $key = $pair['key'];
+            $data = $pair['value'];
             $count++;
+            if ($this->ttl === 0) {
+                $this->store[$key] = array($data, 0);
+            } else {
+                $this->store[$key] = array($data, cache::now());
+            }
         }
         return $count;
     }
@@ -313,6 +331,7 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      * @return bool
      */
     public function has_all(array $keys) {
+        $maxtime = 0;
         if ($this->ttl != 0) {
             $maxtime = cache::now() - $this->ttl;
         }
@@ -335,6 +354,7 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      * @return bool
      */
     public function has_any(array $keys) {
+        $maxtime = 0;
         if ($this->ttl != 0) {
             $maxtime = cache::now() - $this->ttl;
         }
@@ -354,6 +374,9 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      * @return bool Returns true if the operation was a success, false otherwise.
      */
     public function delete($key) {
+        if (!isset($this->store[$key])) {
+            return false;
+        }
         unset($this->store[$key]);
         return true;
     }
@@ -365,6 +388,7 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      * @return int The number of items successfully deleted.
      */
     public function delete_many(array $keys) {
+        // The number of items that have been successfully deleted.
         $count = 0;
         foreach ($keys as $key) {
             unset($this->store[$key]);
@@ -420,12 +444,37 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
         return $this->name;
     }
 
+    /**
+     * Removes expired elements.
+     * @return int number of removed elements
+     */
+    protected function check_ttl() {
+        if ($this->ttl === 0) {
+            return 0;
+        }
+        $maxtime = cache::now() - $this->ttl;
+        $count = 0;
+        for ($value = reset($this->store); $value !== false; $value = next($this->store)) {
+            if ($value[1] >= $maxtime) {
+                // We know that elements are sorted by ttl so no need to continue.
+                break;
+            }
+            $count++;
+        }
+        if ($count) {
+            // Remove first $count elements as they are expired.
+            $this->store = array_slice($this->store, $count, null, true);
+        }
+        return $count;
+    }
+
     /**
      * Finds all of the keys being stored in the cache store instance.
      *
      * @return array
      */
     public function find_all() {
+        $this->check_ttl();
         return array_keys($this->store);
     }
 
@@ -433,6 +482,7 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      * Finds all of the keys whose keys start with the given prefix.
      *
      * @param string $prefix
+     * @return array An array of keys.
      */
     public function find_by_prefix($prefix) {
         $return = array();
@@ -443,4 +493,12 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
         }
         return $return;
     }
+
+    /**
+     * This store supports native TTL handling.
+     * @return bool
+     */
+    public function store_supports_native_ttl() {
+        return true;
+    }
 }
diff --git a/cache/tests/cache_test.php b/cache/tests/cache_test.php
index 26a331d8440..9d36ef6a1f2 100644
--- a/cache/tests/cache_test.php
+++ b/cache/tests/cache_test.php
@@ -1109,9 +1109,9 @@ class cache_phpunit_tests extends advanced_testcase {
     }
 
     /**
-     * Test that multiple loaders work ok.
+     * Test that multiple application loaders work ok.
      */
-    public function test_multiple_loaders() {
+    public function test_multiple_application_loaders() {
         $instance = cache_config_phpunittest::instance(true);
         $instance->phpunit_add_file_store('phpunittest1');
         $instance->phpunit_add_file_store('phpunittest2');
@@ -1156,6 +1156,93 @@ class cache_phpunit_tests extends advanced_testcase {
         $this->assertFalse($result['a']);
         $this->assertEquals('B', $result['b']);
         $this->assertFalse($result['c']);
+
+        // Test non-recursive deletes.
+        $this->assertTrue($cache->set('test', 'test'));
+        $this->assertSame('test', $cache->get('test'));
+        $this->assertTrue($cache->delete('test', false));
+        // We should still have it on a deeper loader.
+        $this->assertSame('test', $cache->get('test'));
+        // Test non-recusive with many functions.
+        $this->assertSame(3, $cache->set_many(array(
+            'one' => 'one',
+            'two' => 'two',
+            'three' => 'three'
+        )));
+        $this->assertSame('one', $cache->get('one'));
+        $this->assertSame(array('two' => 'two', 'three' => 'three'), $cache->get_many(array('two', 'three')));
+        $this->assertSame(3, $cache->delete_many(array('one', 'two', 'three'), false));
+        $this->assertSame('one', $cache->get('one'));
+        $this->assertSame(array('two' => 'two', 'three' => 'three'), $cache->get_many(array('two', 'three')));
+    }
+
+    /**
+     * Test that multiple application loaders work ok.
+     */
+    public function test_multiple_session_loaders() {
+        /* @var cache_config_phpunittest $instance */
+        $instance = cache_config_phpunittest::instance(true);
+        $instance->phpunit_add_session_store('phpunittest1');
+        $instance->phpunit_add_session_store('phpunittest2');
+        $instance->phpunit_add_definition('phpunit/multi_loader', array(
+            'mode' => cache_store::MODE_SESSION,
+            'component' => 'phpunit',
+            'area' => 'multi_loader'
+        ));
+        $instance->phpunit_add_definition_mapping('phpunit/multi_loader', 'phpunittest1', 3);
+        $instance->phpunit_add_definition_mapping('phpunit/multi_loader', 'phpunittest2', 2);
+
+        $cache = cache::make('phpunit', 'multi_loader');
+        $this->assertInstanceOf('cache_session', $cache);
+        $this->assertFalse($cache->get('test'));
+        $this->assertTrue($cache->set('test', 'test'));
+        $this->assertEquals('test', $cache->get('test'));
+        $this->assertTrue($cache->delete('test'));
+        $this->assertFalse($cache->get('test'));
+        $this->assertTrue($cache->set('test', 'test'));
+        $this->assertTrue($cache->purge());
+        $this->assertFalse($cache->get('test'));
+
+        // Test the many commands.
+        $this->assertEquals(3, $cache->set_many(array('a' => 'A', 'b' => 'B', 'c' => 'C')));
+        $result = $cache->get_many(array('a', 'b', 'c'));
+        $this->assertInternalType('array', $result);
+        $this->assertCount(3, $result);
+        $this->assertArrayHasKey('a', $result);
+        $this->assertArrayHasKey('b', $result);
+        $this->assertArrayHasKey('c', $result);
+        $this->assertEquals('A', $result['a']);
+        $this->assertEquals('B', $result['b']);
+        $this->assertEquals('C', $result['c']);
+        $this->assertEquals($result, $cache->get_many(array('a', 'b', 'c')));
+        $this->assertEquals(2, $cache->delete_many(array('a', 'c')));
+        $result = $cache->get_many(array('a', 'b', 'c'));
+        $this->assertInternalType('array', $result);
+        $this->assertCount(3, $result);
+        $this->assertArrayHasKey('a', $result);
+        $this->assertArrayHasKey('b', $result);
+        $this->assertArrayHasKey('c', $result);
+        $this->assertFalse($result['a']);
+        $this->assertEquals('B', $result['b']);
+        $this->assertFalse($result['c']);
+
+        // Test non-recursive deletes.
+        $this->assertTrue($cache->set('test', 'test'));
+        $this->assertSame('test', $cache->get('test'));
+        $this->assertTrue($cache->delete('test', false));
+        // We should still have it on a deeper loader.
+        $this->assertSame('test', $cache->get('test'));
+        // Test non-recusive with many functions.
+        $this->assertSame(3, $cache->set_many(array(
+            'one' => 'one',
+            'two' => 'two',
+            'three' => 'three'
+        )));
+        $this->assertSame('one', $cache->get('one'));
+        $this->assertSame(array('two' => 'two', 'three' => 'three'), $cache->get_many(array('two', 'three')));
+        $this->assertSame(3, $cache->delete_many(array('one', 'two', 'three'), false));
+        $this->assertSame('one', $cache->get('one'));
+        $this->assertSame(array('two' => 'two', 'three' => 'three'), $cache->get_many(array('two', 'three')));
     }
 
     /**
diff --git a/cache/tests/fixtures/lib.php b/cache/tests/fixtures/lib.php
index b68bfd4c8fd..fda991f703a 100644
--- a/cache/tests/fixtures/lib.php
+++ b/cache/tests/fixtures/lib.php
@@ -86,6 +86,24 @@ class cache_config_phpunittest extends cache_config_writer {
         );
     }
 
+    /**
+     * Forcefully adds a session store.
+     *
+     * @param string $name
+     */
+    public function phpunit_add_session_store($name) {
+        $this->configstores[$name] = array(
+            'name' => $name,
+            'plugin' => 'session',
+            'configuration' => array(),
+            'features' => 14,
+            'modes' => 2,
+            'default' => true,
+            'class' => 'cachestore_session',
+            'lock' => 'cachelock_file_default',
+        );
+    }
+
     /**
      * Forcefully injects a definition => store mapping.
      *