Commit 9eb6dd5e authored by Dries's avatar Dries
Browse files

- Patch #251792 by pwolanin, Damien Tournoud, slantview, c960657: added a...

- Patch #251792 by pwolanin, Damien Tournoud, slantview, c960657: added a locking framework for long running operations.
parent b4132364
......@@ -1513,6 +1513,9 @@ function _drupal_bootstrap($phase) {
}
// Prepare for non-cached page workflow.
require_once DRUPAL_ROOT . '/' . variable_get('lock_inc', 'includes/lock.inc');
lock_initialize();
if ($_SERVER['SERVER_SOFTWARE'] !== 'PHP CLI') {
ob_start();
drupal_page_header();
......
<?php
// $Id$
/**
* @file
* A database-mediated implementation of a locking mechanism.
*/
/**
* @defgroup lock Functions to coordinate long-running operations across requests.
* @{
* In most environments, multiple Drupal page requests (a.k.a. threads or
* processes) will execute in parallel. This leads to potential conflicts or
* race conditions when two requests execute the same code at the same time. A
* common example of this is a rebuild like menu_rebuild() where we invoke many
* hook implementations to get and process data from all active modules, and
* then delete the current data in the database to insert the new afterwards.
*
* This is a cooperative, advisory lock system. Any long-running operation
* that could potentially be attempted in parallel by multiple requests should
* try to acquire a lock before proceeding. By obtainng a lock, one request
* notifies any other requests that a specific operation is in progress which
* must not be executed in parallel.
*
* To use this API, pick a unique name for the lock. A sensible choice is the
* name of the function performing the operation. A very simple example use of
* this API:
* @code
* function mymodule_long_operation() {
* if (lock_acquire('mymodule_long_operation')) {
* // Do the long operation here.
* // ...
* lock_release('mymodule_long_operation');
* }
* }
* @endcode
*
* If a function acquires a lock it should always release it when the
* operation is complete by calling lock_release(), as in the example.
*
* A function that has acquired a lock may attempt to renew a lock (extend the
* duration of the lock) by calling lock_acquire() again during the operation.
* Failure to renew a lock is indicative that another request has acquired
* the lock, and that the current operation may need to be aborted.
*
* If a function fails to acquire a lock it may either immediately return, or
* it may call lock_wait() if the rest of the current page request requires
* that the operation in question be complete. After lock_wait() returns,
* the function may again attempt to acquire the lock, or may simply allow the
* page request to proceed on the assumption that a parallel request completed
* the operation.
*
* lock_acquire() and lock_wait() will automatically break (delete) a lock
* whose duration has exceeded the timeout specified when it was acquired.
*
* A function that has acquired a lock may attempt to renew a lock (extend the
* duration of the lock) by calling lock_acquire() again during the operation.
* Failure to renew a lock is indicative that another request has acquired
* the lock, and that the current operation may need to be aborted.
*
* Alternative implementations of this API (such as APC) may be substituted
* by setting the 'lock_inc' variable to an alternate include filepath. Since
* this is an API intended to support alternative implementations, code using
* this API should never rely upon specific implementation details (for example
* no code should look for or directly modify a lock in the {semaphore} table).
*/
/**
* Initialize the locking system.
*/
function lock_initialize() {
global $locks;
$locks = array();
}
/**
* Helper function to get this request's unique id.
*/
function _lock_id() {
$lock_id = &drupal_static(__FUNCTION__);
if (!isset($lock_id)) {
// Assign a unique id.
$lock_id = uniqid(mt_rand(), TRUE);
// We only register a shutdown function if a lock is used.
register_shutdown_function('lock_release_all', $lock_id);
}
return $lock_id;
}
/**
* Acquire (or renew) a lock, but do not block if it fails.
*
* @param $name
* The name of the lock.
* @param $timeout
* A number of seconds (float) before the lock expires (minimum of 0.001).
* @return
* TRUE if the lock was acquired, FALSE if it failed.
*/
function lock_acquire($name, $timeout = 30.0) {
global $locks;
// Insure that the timeout is at least 1 ms.
$timeout = max($timeout, 0.001);
$expire = microtime(TRUE) + $timeout;
if (isset($locks[$name])) {
// Try to extend the expiration of a lock we already acquired.
$success = (bool) db_update('semaphore')
->fields(array('expire' => $expire))
->condition('name', $name)
->condition('value', _lock_id())
->execute();
if (!$success) {
// The lock was broken.
unset($locks[$name]);
}
return $success;
}
else {
// Optimistically try to acquire the lock, then retry once if it fails.
// The first time through the loop cannot be a retry.
$retry = FALSE;
// We always want to do this code at least once.
do {
try {
db_insert('semaphore')
->fields(array(
'name' => $name,
'value' => _lock_id(),
'expire' => $expire,
))
->execute();
// We track all acquired locks in the global variable.
$locks[$name] = TRUE;
// We never need to try again.
$retry = FALSE;
}
catch (PDOException $e) {
// Suppress the error. If this is our first pass through the loop,
// then $retry is FALSE. In this case, the insert must have failed
// meaning some other request acquired the lock but did not release it.
// We decide whether to retry by checking lock_may_be_available()
// Since this will break the lock in case it is expired.
$retry = $retry ? FALSE : lock_may_be_available($name);
}
// We only retry in case the first attempt failed, but we then broke
// an expired lock.
} while ($retry);
}
return isset($locks[$name]);
}
/**
* Check if lock acquired by a different process may be available.
*
* If an existing lock has expired, it is removed.
*
* @param $name
* The name of the lock.
* @return
* TRUE if there is no lock or it was removed, FALSE otherwise.
*/
function lock_may_be_available($name) {
$lock = db_query('SELECT expire, value FROM {semaphore} WHERE name = :name', array(':name' => $name))->fetchAssoc();
if (!$lock) {
return TRUE;
}
$expire = (float) $lock['expire'];
$now = microtime(TRUE);
if ($now > $expire) {
// We check two conditions to prevent a race condition where another
// request acquired the lock and set a new expire time. We add a small
// number to $expire to avoid errors with float to string conversion.
return (bool) db_delete('semaphore')
->condition('name', $name)
->condition('value', $lock['value'])
->condition('expire', 0.0001 + $expire, '<=')
->execute();
}
return FALSE;
}
/**
* Wait for a lock to be available.
*
* This function may be called in a request that fails to acquire a desired
* lock. This will block further execution until the lock is available or the
* specified delay in seconds is reached. This should not be used with locks
* that are acquired very frequently, since the lock is likely to be acquired
* again by a different request during the sleep().
*
* @param $name
* The name of the lock.
* @param $delay
* The maximum number of seconds to wait, as an integer.
* @return
* TRUE if the lock holds, FALSE if it is available.
*/
function lock_wait($name, $delay = 30) {
$delay = (int) $delay;
while ($delay--) {
// This function should only be called by a request that failed to get a
// lock, so we sleep first to give the parallel request a chance to finish
// and release the lock.
sleep(1);
if (lock_may_be_available($name)) {
// No longer need to wait.
return FALSE;
}
}
// The caller must still wait longer to get the lock.
return TRUE;
}
/**
* Release a lock previously acquired by lock_acquire().
*
* This will release the named lock if it is still held by the current request.
*
* @param $name
* The name of the lock.
*/
function lock_release($name) {
global $locks;
unset($locks[$name]);
db_delete('semaphore')
->condition('name', $name)
->condition('value', _lock_id())
->execute();
}
/**
* Release all previously acquired locks.
*/
function lock_release_all($lock_id = NULL) {
global $locks;
$locks = array();
if (empty($lock_id)) {
$lock_id = _lock_id();
}
db_delete('semaphore')
->condition('value', $lock_id)
->execute();
}
/**
* @} End of "defgroup lock".
*/
......@@ -1835,18 +1835,35 @@ function menu_cache_clear_all() {
* schedule a call to itself on the first real page load from
* menu_execute_active_handler(), because the maintenance page environment
* is different and leaves stale data in the menu tables.
*
* @return
* TRUE if the menu was rebuilt, FALSE if another thread was rebuilding
* in parallel and the current thread just waited for completion.
*/
function menu_rebuild() {
variable_del('menu_rebuild_needed');
if (!lock_acquire('menu_rebuild')) {
// Wait for another request that is already doing this work.
// We choose to block here since otherwise the router item may not
// be available in menu_execute_active_handler() resulting in a 404.
lock_wait('menu_rebuild');
return FALSE;
}
list($menu, $masks) = menu_router_build();
_menu_router_save($menu, $masks);
_menu_navigation_links_rebuild($menu);
// Clear the menu, page and block caches.
menu_cache_clear_all();
// Clear the page and block caches.
_menu_clear_page_cache();
if (defined('MAINTENANCE_MODE')) {
variable_set('menu_rebuild_needed', TRUE);
}
else {
variable_del('menu_rebuild_needed');
}
lock_release('menu_rebuild');
return TRUE;
}
/**
......
......@@ -375,7 +375,7 @@ function locale($string = NULL, $context = NULL, $langcode = NULL, $reset = FALS
if ($cache = cache_get('locale:' . $langcode, 'cache')) {
$locale_t[$langcode] = $cache->data;
}
else {
elseif (lock_acquire('locale_cache_' . $langcode)) {
// Refresh database stored cache of translations for given language.
// We only store short strings used in current version, to improve
// performance and consume less memory.
......@@ -384,6 +384,7 @@ function locale($string = NULL, $context = NULL, $langcode = NULL, $reset = FALS
$locale_t[$langcode][$data->context][$data->source] = (empty($data->translation) ? TRUE : $data->translation);
}
cache_set('locale:' . $langcode, $locale_t[$langcode]);
lock_release('locale_cache_' . $langcode);
}
}
}
......
......@@ -24,6 +24,7 @@ files[] = tests/filetransfer.test
files[] = tests/form.test
files[] = tests/graph.test
files[] = tests/image.test
files[] = tests/lock.test
files[] = tests/menu.test
files[] = tests/module.test
files[] = tests/registry.test
......
<?php
// $Id$
/**
* Tests for the lock system.
*/
class LockFunctionalTest extends DrupalWebTestCase {
public static function getInfo() {
return array(
'name' => 'Locking framework tests',
'description' => 'Confirm locking works between two separate requests.',
'group' => 'System',
);
}
function setUp() {
parent::setUp('system_test');
}
/**
* Confirm that we can acquire and release locks in two parallel requests.
*/
function testLockAcquire() {
$lock_acquired = 'TRUE: Lock successfully acquired in system_test_lock_acquire()';
$lock_not_acquired = 'FALSE: Lock not acquired in system_test_lock_acquire()';
$this->assertTrue(lock_acquire('system_test_lock_acquire'), t('Lock acquired by this request.'), t('Lock'));
$this->assertTrue(lock_acquire('system_test_lock_acquire'), t('Lock extended by this request.'), t('Lock'));
lock_release('system_test_lock_acquire');
// Cause another request to acquire the lock.
$this->drupalGet('system-test/lock-acquire');
$this->assertText($lock_acquired, t('Lock acquired by the other request.'), t('Lock'));
// The other request has finished, thus it should have released its lock.
$this->assertTrue(lock_acquire('system_test_lock_acquire'), t('Lock acquired by this request.'), t('Lock'));
// This request holds the lock, so the other request cannot acquire it.
$this->drupalGet('system-test/lock-acquire');
$this->assertText($lock_not_acquired, t('Lock not acquired by the other request.'), t('Lock'));
lock_release('system_test_lock_acquire');
// Try a very short timeout and lock breaking.
$this->assertTrue(lock_acquire('system_test_lock_acquire', 0.5), t('Lock acquired by this request.'), t('Lock'));
sleep(1);
// The other request should break our lock.
$this->drupalGet('system-test/lock-acquire');
$this->assertText($lock_acquired, t('Lock acquired by the other request, breaking our lock.'), t('Lock'));
// We cannot renew it, since the other thread took it.
$this->assertFalse(lock_acquire('system_test_lock_acquire'), t('Lock cannot be extended by this request.'), t('Lock'));
// Check the shut-down function.
$lock_acquired_exit = 'TRUE: Lock successfully acquired in system_test_lock_exit()';
$lock_not_acquired_exit = 'FALSE: Lock not acquired in system_test_lock_exit()';
$this->drupalGet('system-test/lock-exit');
$this->assertText($lock_acquired_exit, t('Lock acquired by the other request before exit.'), t('Lock'));
$this->assertTrue(lock_acquire('system_test_lock_exit'), t('Lock acquired by this request after the other request exits.'), t('Lock'));
}
}
......@@ -59,6 +59,20 @@ function system_test_menu() {
'type' => MENU_CALLBACK,
);
$items['system-test/lock-acquire'] = array(
'title' => 'Lock acquire',
'page callback' => 'system_test_lock_acquire',
'access callback' => TRUE,
'type' => MENU_CALLBACK,
);
$items['system-test/lock-exit'] = array(
'title' => 'Lock acquire then exit',
'page callback' => 'system_test_lock_exit',
'access callback' => TRUE,
'type' => MENU_CALLBACK,
);
return $items;
}
......@@ -185,3 +199,29 @@ function system_test_system_info_alter(&$info, $file) {
}
}
/**
* Try to acquire a named lock and report the outcome.
*/
function system_test_lock_acquire() {
if (lock_acquire('system_test_lock_acquire')) {
lock_release('system_test_lock_acquire');
return 'TRUE: Lock successfully acquired in system_test_lock_acquire()';
}
else {
return 'FALSE: Lock not acquired in system_test_lock_acquire()';
}
}
/**
* Try to acquire a specific lock, and then exit.
*/
function system_test_lock_exit() {
if (lock_acquire('system_test_lock_exit', 900)) {
echo 'TRUE: Lock successfully acquired in system_test_lock_exit()';
// The shut-down function should release the lock.
exit();
}
else {
return 'FALSE: Lock not acquired in system_test_lock_exit()';
}
}
......@@ -1265,6 +1265,34 @@ function system_schema() {
'primary key' => array('filename'),
);
$schema['semaphore'] = array(
'description' => 'Table for holding semaphores, locks, flags, etc. that cannot be stored as Drupal variables since they must not be cached.',
'fields' => array(
'name' => array(
'description' => 'Primary Key: Unique name.',
'type' => 'varchar',
'length' => 255,
'not null' => TRUE,
'default' => ''
),
'value' => array(
'description' => 'A value for the semaphore.',
'type' => 'varchar',
'length' => 255,
'not null' => TRUE,
'default' => ''
),
'expire' => array(
'description' => 'A Unix timestamp with microseconds indicating when the semaphore should expire.',
'type' => 'float',
'size' => 'big',
'not null' => TRUE
),
),
'indexes' => array('value' => array('value')),
'primary key' => array('name'),
);
$schema['sessions'] = array(
'description' => "Drupal's session handlers read and write into the sessions table. Each record represents a user session, either anonymous or authenticated.",
'fields' => array(
......
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