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statecache.php
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statecache.php
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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
/**
* Defines the qbehaviour_opaque_state_cache class.
*
* @package qbehaviour_opaque
* @copyright 2011 Antti Andreimann
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
/**
* Caches opaque states in the session.
*
* This is a singleton class, which is important, becuase we want one instance
* per requests that does things with Opaque questions. That is how we ensure
* we expire no longer required cache entries.
*
* @copyright 2011 Antti Andreimann
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
class qbehaviour_opaque_state_cache {
const MAX_IDLE_LIFETIME = 2;
/** @var array reference to where the data is acutally stored in the session. */
protected $cache;
/** @var qbehaviour_opaque_cache_manager singleton instance. */
protected static $instance = null;
/**
* Constructor.
*/
protected function __construct() {
global $SESSION;
if (!isset($SESSION->qtype_opaque_state_cache) ||
!is_array($SESSION->qtype_opaque_state_cache)) {
$SESSION->qtype_opaque_state_cache = array();
}
$this->cache = &$SESSION->qtype_opaque_state_cache;
$this->age_all_entries();
// It would be better to do this at the end of the request, just before
// the session is written out, rather than the next time this class is
// created. However, I cannot currently find a way to hook into that
// moment. Neither a destructor for this class, nor register_shutdown_function
// works. They both happen after the session has been closed.
$this->discard_old_entries();
}
/**
* Get the cache manager instance associated with the current
* user session or create a new one if it does not exist.
*
* @return qbehaviour_cache_manager the cache manager instance
*/
public static function get() {
if (is_null(self::$instance)) {
self::$instance = new self();
}
return self::$instance;
}
/**
* Useful for debugging.
*
* For example add public function __destruct() { echo $this; } to this class
* to output the cache state on any page that uses this cache.
*
* @return string representation of the state of the cache.
*/
public function __toString() {
$string = '';
foreach ($this->cache as $state) {
$string .= $state->cachekey . ' => [' . $state->questionsessionid . ', ' .
$state->sequencenumber . ', ' . $state->age . "]\n";
}
return $string;
}
/**
* Load the cached state from the store.
*
* @param string $key a unique key for this cached entry
* @return object|null On success, a cached opaque state,
* null if there was no usable cached state to return.
*/
public function load($key) {
if (!array_key_exists($key, $this->cache)) {
return null;
}
return $this->cache[$key];
}
/**
* Save or update the cached state
*
* @param string $key a unique key for this cached entry
* @param object $state the opaque state to save
*/
public function save($key, $state) {
if (array_key_exists($key, $this->cache)) {
// If we already have some other state at this cache key, delete it.
$this->delete($this->cache[$key]);
}
$state->cachekey = $key;
$this->mark_fresh($state);
$this->cache[$key] = $state;
}
/**
* Delete the cached state, making sure that any remote session associated
* with it is closed.
*
* @param object $state the state to remove.
*/
public function delete($state) {
// Try to stop any active question session.
if (!empty($state->questionsessionid) && !empty($state->engine)) {
try {
$connection = new qbehaviour_opaque_connection($state->engine);
$connection->stop($state->questionsessionid);
$state->questionsessionid = null;
} catch (SoapFault $e) { // @codingStandardsIgnoreLine
// ... but ignore any errors when doing so.
}
}
// Remove from the cache, if it is there.
if (!empty($state->cachekey)) {
unset($this->cache[$state->cachekey]);
}
}
/**
* Reset the age of a cached entry to 0.
* @param object $state a cache entry.
*/
public function mark_fresh($state) {
$state->timemodified = time();
$state->age = 0;
}
/**
* Increase the age of all cache entries by one.
*/
protected function age_all_entries() {
foreach ($this->cache as $state) {
$state->age += 1;
}
}
/**
* Discard any entries whose age is greater than MAX_IDLE_LIFETIME.
*/
protected function discard_old_entries() {
foreach ($this->cache as $state) {
if ($state->age >= self::MAX_IDLE_LIFETIME) {
$this->delete($state);
}
}
}
/**
* Cache the last used set of question display options.
* @param question_display_options $options
*/
public function set_last_used_options($options) {
global $SESSION;
if (is_null($options)) {
return;
}
if (!isset($SESSION->qtype_opaque_option_cache)) {
$SESSION->qtype_opaque_option_cache = new stdClass();
}
$SESSION->qtype_opaque_option_cache->readonly = $options->readonly;
$SESSION->qtype_opaque_option_cache->marks = $options->marks;
$SESSION->qtype_opaque_option_cache->markdp = $options->markdp;
$SESSION->qtype_opaque_option_cache->correctness = $options->correctness;
$SESSION->qtype_opaque_option_cache->feedback = $options->feedback;
$SESSION->qtype_opaque_option_cache->generalfeedback = $options->generalfeedback;
}
/**
* @return object the last used set of question display options.
*/
public function get_last_used_options() {
global $SESSION;
if (!empty($SESSION->qtype_opaque_option_cache)) {
return $SESSION->qtype_opaque_option_cache;
} else {
return null;
}
}
}