3 * Interface and manager for deferred updates.
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License along
16 * with this program; if not, write to the Free Software Foundation, Inc.,
17 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
18 * http://www.gnu.org/copyleft/gpl.html
22 use MediaWiki\MediaWikiServices
;
25 * Class for managing the deferred updates
27 * In web request mode, deferred updates can be run at the end of the request, either before or
28 * after the HTTP response has been sent. In either case, they run after the DB commit step. If
29 * an update runs after the response is sent, it will not block clients. If sent before, it will
30 * run synchronously. These two modes are defined via PRESEND and POSTSEND constants, the latter
31 * being the default for addUpdate() and addCallableUpdate().
33 * Updates that work through this system will be more likely to complete by the time the client
34 * makes their next request after this one than with the JobQueue system.
36 * In CLI mode, updates run immediately if no DB writes are pending. Otherwise, they run when:
37 * - a) Any waitForReplication() call if no writes are pending on any DB
38 * - b) A commit happens on Maintenance::getDB( DB_MASTER ) if no writes are pending on any DB
39 * - c) EnqueueableDataUpdate tasks may enqueue on commit of Maintenance::getDB( DB_MASTER )
40 * - d) At the completion of Maintenance::execute()
42 * When updates are deferred, they go into one two FIFO "top-queues" (one for pre-send and one
43 * for post-send). Updates enqueued *during* doUpdate() of a "top" update go into the "sub-queue"
44 * for that update. After that method finishes, the sub-queue is run until drained. This continues
45 * for each top-queue job until the entire top queue is drained. This happens for the pre-send
46 * top-queue, and later on, the post-send top-queue, in execute().
50 class DeferredUpdates
{
51 /** @var DeferrableUpdate[] Updates to be deferred until before request end */
52 private static $preSendUpdates = [];
53 /** @var DeferrableUpdate[] Updates to be deferred until after request end */
54 private static $postSendUpdates = [];
56 const ALL
= 0; // all updates; in web requests, use only after flushing the output buffer
57 const PRESEND
= 1; // for updates that should run before flushing output buffer
58 const POSTSEND
= 2; // for updates that should run after flushing output buffer
60 const BIG_QUEUE_SIZE
= 100;
62 /** @var array|null Information about the current execute() call or null if not running */
63 private static $executeContext;
66 * Add an update to the deferred list to be run later by execute()
68 * In CLI mode, callback magic will also be used to run updates when safe
70 * @param DeferrableUpdate $update Some object that implements doUpdate()
71 * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
73 public static function addUpdate( DeferrableUpdate
$update, $stage = self
::POSTSEND
) {
74 global $wgCommandLineMode;
76 // This is a sub-DeferredUpdate, run it right after its parent update
77 if ( self
::$executeContext && self
::$executeContext['stage'] >= $stage ) {
78 self
::$executeContext['subqueue'][] = $update;
82 if ( $stage === self
::PRESEND
) {
83 self
::push( self
::$preSendUpdates, $update );
85 self
::push( self
::$postSendUpdates, $update );
88 // Try to run the updates now if in CLI mode and no transaction is active.
89 // This covers scripts that don't/barely use the DB but make updates to other stores.
90 if ( $wgCommandLineMode ) {
91 self
::tryOpportunisticExecute( 'run' );
96 * Add a callable update. In a lot of cases, we just need a callback/closure,
97 * defining a new DeferrableUpdate object is not necessary
99 * @see MWCallableUpdate::__construct()
101 * @param callable $callable
102 * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
103 * @param IDatabase|null $dbw Abort if this DB is rolled back [optional] (since 1.28)
105 public static function addCallableUpdate(
106 $callable, $stage = self
::POSTSEND
, IDatabase
$dbw = null
108 self
::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dbw ), $stage );
112 * Do any deferred updates and clear the list
114 * @param string $mode Use "enqueue" to use the job queue when possible [Default: "run"]
115 * @param integer $stage DeferredUpdates constant (PRESEND, POSTSEND, or ALL) (since 1.27)
117 public static function doUpdates( $mode = 'run', $stage = self
::ALL
) {
118 $stageEffective = ( $stage === self
::ALL
) ? self
::POSTSEND
: $stage;
120 if ( $stage === self
::ALL ||
$stage === self
::PRESEND
) {
121 self
::execute( self
::$preSendUpdates, $mode, $stageEffective );
124 if ( $stage === self
::ALL ||
$stage == self
::POSTSEND
) {
125 self
::execute( self
::$postSendUpdates, $mode, $stageEffective );
130 * @param DeferrableUpdate[] $queue
131 * @param DeferrableUpdate $update
133 private static function push( array &$queue, DeferrableUpdate
$update ) {
134 if ( $update instanceof MergeableUpdate
) {
135 $class = get_class( $update ); // fully-qualified class
136 if ( isset( $queue[$class] ) ) {
137 /** @var $existingUpdate MergeableUpdate */
138 $existingUpdate = $queue[$class];
139 $existingUpdate->merge( $update );
141 $queue[$class] = $update;
149 * Immediately run/queue a list of updates
151 * @param DeferrableUpdate[] &$queue List of DeferrableUpdate objects
152 * @param string $mode Use "enqueue" to use the job queue when possible
153 * @param integer $stage Class constant (PRESEND, POSTSEND) (since 1.28)
154 * @throws ErrorPageError Happens on top-level calls
155 * @throws Exception Happens on second-level calls
157 protected static function execute( array &$queue, $mode, $stage ) {
158 $services = MediaWikiServices
::getInstance();
159 $stats = $services->getStatsdDataFactory();
160 $lbFactory = $services->getDBLoadBalancerFactory();
161 $method = RequestContext
::getMain()->getRequest()->getMethod();
163 $ticket = $lbFactory->getEmptyTransactionTicket( __METHOD__
);
165 /** @var ErrorPageError $reportableError */
166 $reportableError = null;
167 /** @var DeferrableUpdate[] $updates Snapshot of queue */
170 // Keep doing rounds of updates until none get enqueued...
172 $queue = []; // clear the queue
174 if ( $mode === 'enqueue' ) {
176 // Push enqueuable updates to the job queue and get the rest
177 $updates = self
::enqueueUpdates( $updates );
178 } catch ( Exception
$e ) {
179 // Let other updates have a chance to run if this failed
180 MWExceptionHandler
::rollbackMasterChangesAndLog( $e );
184 // Order will be DataUpdate followed by generic DeferrableUpdate tasks
185 $updatesByType = [ 'data' => [], 'generic' => [] ];
186 foreach ( $updates as $du ) {
187 if ( $du instanceof DataUpdate
) {
188 $du->setTransactionTicket( $ticket );
189 $updatesByType['data'][] = $du;
191 $updatesByType['generic'][] = $du;
194 $name = ( $du instanceof DeferrableCallback
)
195 ?
get_class( $du ) . '-' . $du->getOrigin()
197 $stats->increment( 'deferred_updates.' . $method . '.' . $name );
200 // Execute all remaining tasks...
201 foreach ( $updatesByType as $updatesForType ) {
202 foreach ( $updatesForType as $update ) {
203 self
::$executeContext = [
208 /** @var DeferrableUpdate $update */
209 $guiError = self
::runUpdate( $update, $lbFactory, $stage );
210 $reportableError = $reportableError ?
: $guiError;
211 // Do the subqueue updates for $update until there are none
212 while ( self
::$executeContext['subqueue'] ) {
213 $subUpdate = reset( self
::$executeContext['subqueue'] );
214 $firstKey = key( self
::$executeContext['subqueue'] );
215 unset( self
::$executeContext['subqueue'][$firstKey] );
217 $guiError = self
::runUpdate( $subUpdate, $lbFactory, $stage );
218 $reportableError = $reportableError ?
: $guiError;
220 self
::$executeContext = null;
224 $updates = $queue; // new snapshot of queue (check for new entries)
227 if ( $reportableError ) {
228 throw $reportableError; // throw the first of any GUI errors
233 * @param DeferrableUpdate $update
234 * @param LBFactory $lbFactory
235 * @param integer $stage
236 * @return ErrorPageError|null
238 private static function runUpdate( DeferrableUpdate
$update, LBFactory
$lbFactory, $stage ) {
241 $fnameTrxOwner = get_class( $update ) . '::doUpdate';
242 $lbFactory->beginMasterChanges( $fnameTrxOwner );
244 $lbFactory->commitMasterChanges( $fnameTrxOwner );
245 } catch ( Exception
$e ) {
246 // Reporting GUI exceptions does not work post-send
247 if ( $e instanceof ErrorPageError
&& $stage === self
::PRESEND
) {
250 MWExceptionHandler
::rollbackMasterChangesAndLog( $e );
257 * Run all deferred updates immediately if there are no DB writes active
259 * If $mode is 'run' but there are busy databates, EnqueueableDataUpdate
260 * tasks will be enqueued anyway for the sake of progress.
262 * @param string $mode Use "enqueue" to use the job queue when possible
263 * @return bool Whether updates were allowed to run
266 public static function tryOpportunisticExecute( $mode = 'run' ) {
267 // execute() loop is already running
268 if ( self
::$executeContext ) {
272 // Avoiding running updates without them having outer scope
273 if ( !self
::getBusyDbConnections() ) {
274 self
::doUpdates( $mode );
278 if ( self
::pendingUpdatesCount() >= self
::BIG_QUEUE_SIZE
) {
279 // If we cannot run the updates with outer transaction context, try to
280 // at least enqueue all the updates that support queueing to job queue
281 self
::$preSendUpdates = self
::enqueueUpdates( self
::$preSendUpdates );
282 self
::$postSendUpdates = self
::enqueueUpdates( self
::$postSendUpdates );
285 return !self
::pendingUpdatesCount();
289 * Enqueue a job for each EnqueueableDataUpdate item and return the other items
291 * @param DeferrableUpdate[] $updates A list of deferred update instances
292 * @return DeferrableUpdate[] Remaining updates that do not support being queued
294 private static function enqueueUpdates( array $updates ) {
297 foreach ( $updates as $update ) {
298 if ( $update instanceof EnqueueableDataUpdate
) {
299 $spec = $update->getAsJobSpecification();
300 JobQueueGroup
::singleton( $spec['wiki'] )->push( $spec['job'] );
302 $remaining[] = $update;
310 * @return integer Number of enqueued updates
313 public static function pendingUpdatesCount() {
314 return count( self
::$preSendUpdates ) +
count( self
::$postSendUpdates );
318 * Clear all pending updates without performing them. Generally, you don't
319 * want or need to call this. Unit tests need it though.
321 public static function clearPendingUpdates() {
322 self
::$preSendUpdates = [];
323 self
::$postSendUpdates = [];
327 * @return IDatabase[] Connection where commit() cannot be called yet
329 private static function getBusyDbConnections() {
332 $lbFactory = MediaWikiServices
::getInstance()->getDBLoadBalancerFactory();
333 $lbFactory->forEachLB( function ( LoadBalancer
$lb ) use ( &$connsBusy ) {
334 $lb->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( &$connsBusy ) {
335 if ( $conn->writesOrCallbacksPending() ||
$conn->explicitTrxActive() ) {
336 $connsBusy[] = $conn;