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 Wikimedia\Rdbms\IDatabase
;
23 use MediaWiki\MediaWikiServices
;
24 use Wikimedia\Rdbms\LBFactory
;
25 use Wikimedia\Rdbms\LoadBalancer
;
28 * Class for managing the deferred updates
30 * In web request mode, deferred updates can be run at the end of the request, either before or
31 * after the HTTP response has been sent. In either case, they run after the DB commit step. If
32 * an update runs after the response is sent, it will not block clients. If sent before, it will
33 * run synchronously. These two modes are defined via PRESEND and POSTSEND constants, the latter
34 * being the default for addUpdate() and addCallableUpdate().
36 * Updates that work through this system will be more likely to complete by the time the client
37 * makes their next request after this one than with the JobQueue system.
39 * In CLI mode, updates run immediately if no DB writes are pending. Otherwise, they run when:
40 * - a) Any waitForReplication() call if no writes are pending on any DB
41 * - b) A commit happens on Maintenance::getDB( DB_MASTER ) if no writes are pending on any DB
42 * - c) EnqueueableDataUpdate tasks may enqueue on commit of Maintenance::getDB( DB_MASTER )
43 * - d) At the completion of Maintenance::execute()
45 * When updates are deferred, they go into one two FIFO "top-queues" (one for pre-send and one
46 * for post-send). Updates enqueued *during* doUpdate() of a "top" update go into the "sub-queue"
47 * for that update. After that method finishes, the sub-queue is run until drained. This continues
48 * for each top-queue job until the entire top queue is drained. This happens for the pre-send
49 * top-queue, and later on, the post-send top-queue, in execute().
53 class DeferredUpdates
{
54 /** @var DeferrableUpdate[] Updates to be deferred until before request end */
55 private static $preSendUpdates = [];
56 /** @var DeferrableUpdate[] Updates to be deferred until after request end */
57 private static $postSendUpdates = [];
59 const ALL
= 0; // all updates; in web requests, use only after flushing the output buffer
60 const PRESEND
= 1; // for updates that should run before flushing output buffer
61 const POSTSEND
= 2; // for updates that should run after flushing output buffer
63 const BIG_QUEUE_SIZE
= 100;
65 /** @var array|null Information about the current execute() call or null if not running */
66 private static $executeContext;
69 * Add an update to the deferred list to be run later by execute()
71 * In CLI mode, callback magic will also be used to run updates when safe
73 * @param DeferrableUpdate $update Some object that implements doUpdate()
74 * @param int $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
76 public static function addUpdate( DeferrableUpdate
$update, $stage = self
::POSTSEND
) {
77 global $wgCommandLineMode;
79 if ( self
::$executeContext && self
::$executeContext['stage'] >= $stage ) {
80 // This is a sub-DeferredUpdate; run it right after its parent update.
81 // Also, while post-send updates are running, push any "pre-send" jobs to the
82 // active post-send queue to make sure they get run this round (or at all).
83 self
::$executeContext['subqueue'][] = $update;
88 if ( $stage === self
::PRESEND
) {
89 self
::push( self
::$preSendUpdates, $update );
91 self
::push( self
::$postSendUpdates, $update );
94 // Try to run the updates now if in CLI mode and no transaction is active.
95 // This covers scripts that don't/barely use the DB but make updates to other stores.
96 if ( $wgCommandLineMode ) {
97 self
::tryOpportunisticExecute( 'run' );
102 * Add a callable update. In a lot of cases, we just need a callback/closure,
103 * defining a new DeferrableUpdate object is not necessary
105 * @see MWCallableUpdate::__construct()
107 * @param callable $callable
108 * @param int $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
109 * @param IDatabase|IDatabase[]|null $dbw Abort if this DB is rolled back [optional] (since 1.28)
111 public static function addCallableUpdate(
112 $callable, $stage = self
::POSTSEND
, $dbw = null
114 self
::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dbw ), $stage );
118 * Do any deferred updates and clear the list
120 * @param string $mode Use "enqueue" to use the job queue when possible [Default: "run"]
121 * @param int $stage DeferredUpdates constant (PRESEND, POSTSEND, or ALL) (since 1.27)
123 public static function doUpdates( $mode = 'run', $stage = self
::ALL
) {
124 $stageEffective = ( $stage === self
::ALL
) ? self
::POSTSEND
: $stage;
126 if ( $stage === self
::ALL ||
$stage === self
::PRESEND
) {
127 self
::execute( self
::$preSendUpdates, $mode, $stageEffective );
130 if ( $stage === self
::ALL ||
$stage == self
::POSTSEND
) {
131 self
::execute( self
::$postSendUpdates, $mode, $stageEffective );
136 * @param bool $value Whether to just immediately run updates in addUpdate()
138 * @deprecated 1.29 Causes issues in Web-executed jobs - see T165714 and T100085.
140 public static function setImmediateMode( $value ) {
141 wfDeprecated( __METHOD__
, '1.29' );
145 * @param DeferrableUpdate[] $queue
146 * @param DeferrableUpdate $update
148 private static function push( array &$queue, DeferrableUpdate
$update ) {
149 if ( $update instanceof MergeableUpdate
) {
150 $class = get_class( $update ); // fully-qualified class
151 if ( isset( $queue[$class] ) ) {
152 /** @var MergeableUpdate $existingUpdate */
153 $existingUpdate = $queue[$class];
154 $existingUpdate->merge( $update );
156 $queue[$class] = $update;
164 * Immediately run/queue a list of updates
166 * @param DeferrableUpdate[] &$queue List of DeferrableUpdate objects
167 * @param string $mode Use "enqueue" to use the job queue when possible
168 * @param int $stage Class constant (PRESEND, POSTSEND) (since 1.28)
169 * @throws ErrorPageError Happens on top-level calls
170 * @throws Exception Happens on second-level calls
172 protected static function execute( array &$queue, $mode, $stage ) {
173 $services = MediaWikiServices
::getInstance();
174 $stats = $services->getStatsdDataFactory();
175 $lbFactory = $services->getDBLoadBalancerFactory();
176 $method = RequestContext
::getMain()->getRequest()->getMethod();
178 $ticket = $lbFactory->getEmptyTransactionTicket( __METHOD__
);
180 /** @var ErrorPageError $reportableError */
181 $reportableError = null;
182 /** @var DeferrableUpdate[] $updates Snapshot of queue */
185 // Keep doing rounds of updates until none get enqueued...
187 $queue = []; // clear the queue
189 // Order will be DataUpdate followed by generic DeferrableUpdate tasks
190 $updatesByType = [ 'data' => [], 'generic' => [] ];
191 foreach ( $updates as $du ) {
192 if ( $du instanceof DataUpdate
) {
193 $du->setTransactionTicket( $ticket );
194 $updatesByType['data'][] = $du;
196 $updatesByType['generic'][] = $du;
199 $name = ( $du instanceof DeferrableCallback
)
200 ?
get_class( $du ) . '-' . $du->getOrigin()
202 $stats->increment( 'deferred_updates.' . $method . '.' . $name );
205 // Execute all remaining tasks...
206 foreach ( $updatesByType as $updatesForType ) {
207 foreach ( $updatesForType as $update ) {
208 self
::$executeContext = [ 'stage' => $stage, 'subqueue' => [] ];
209 /** @var DeferrableUpdate $update */
210 $guiError = self
::runUpdate( $update, $lbFactory, $mode, $stage );
211 $reportableError = $reportableError ?
: $guiError;
212 // Do the subqueue updates for $update until there are none
213 while ( self
::$executeContext['subqueue'] ) {
214 $subUpdate = reset( self
::$executeContext['subqueue'] );
215 $firstKey = key( self
::$executeContext['subqueue'] );
216 unset( self
::$executeContext['subqueue'][$firstKey] );
218 if ( $subUpdate instanceof DataUpdate
) {
219 $subUpdate->setTransactionTicket( $ticket );
222 $guiError = self
::runUpdate( $subUpdate, $lbFactory, $mode, $stage );
223 $reportableError = $reportableError ?
: $guiError;
225 self
::$executeContext = null;
229 $updates = $queue; // new snapshot of queue (check for new entries)
232 if ( $reportableError ) {
233 throw $reportableError; // throw the first of any GUI errors
238 * @param DeferrableUpdate $update
239 * @param LBFactory $lbFactory
240 * @param string $mode
242 * @return ErrorPageError|null
244 private static function runUpdate(
245 DeferrableUpdate
$update, LBFactory
$lbFactory, $mode, $stage
249 if ( $mode === 'enqueue' && $update instanceof EnqueueableDataUpdate
) {
250 // Run only the job enqueue logic to complete the update later
251 $spec = $update->getAsJobSpecification();
252 JobQueueGroup
::singleton( $spec['wiki'] )->push( $spec['job'] );
253 } elseif ( $update instanceof TransactionRoundDefiningUpdate
) {
256 // Run the bulk of the update now
257 $fnameTrxOwner = get_class( $update ) . '::doUpdate';
258 $lbFactory->beginMasterChanges( $fnameTrxOwner );
260 $lbFactory->commitMasterChanges( $fnameTrxOwner );
262 } catch ( Exception
$e ) {
263 // Reporting GUI exceptions does not work post-send
264 if ( $e instanceof ErrorPageError
&& $stage === self
::PRESEND
) {
267 MWExceptionHandler
::rollbackMasterChangesAndLog( $e );
274 * Run all deferred updates immediately if there are no DB writes active
276 * If $mode is 'run' but there are busy databates, EnqueueableDataUpdate
277 * tasks will be enqueued anyway for the sake of progress.
279 * @param string $mode Use "enqueue" to use the job queue when possible
280 * @return bool Whether updates were allowed to run
283 public static function tryOpportunisticExecute( $mode = 'run' ) {
284 // execute() loop is already running
285 if ( self
::$executeContext ) {
289 // Avoiding running updates without them having outer scope
290 if ( !self
::areDatabaseTransactionsActive() ) {
291 self
::doUpdates( $mode );
295 if ( self
::pendingUpdatesCount() >= self
::BIG_QUEUE_SIZE
) {
296 // If we cannot run the updates with outer transaction context, try to
297 // at least enqueue all the updates that support queueing to job queue
298 self
::$preSendUpdates = self
::enqueueUpdates( self
::$preSendUpdates );
299 self
::$postSendUpdates = self
::enqueueUpdates( self
::$postSendUpdates );
302 return !self
::pendingUpdatesCount();
306 * Enqueue a job for each EnqueueableDataUpdate item and return the other items
308 * @param DeferrableUpdate[] $updates A list of deferred update instances
309 * @return DeferrableUpdate[] Remaining updates that do not support being queued
311 private static function enqueueUpdates( array $updates ) {
314 foreach ( $updates as $update ) {
315 if ( $update instanceof EnqueueableDataUpdate
) {
316 $spec = $update->getAsJobSpecification();
317 JobQueueGroup
::singleton( $spec['wiki'] )->push( $spec['job'] );
319 $remaining[] = $update;
327 * @return int Number of enqueued updates
330 public static function pendingUpdatesCount() {
331 return count( self
::$preSendUpdates ) +
count( self
::$postSendUpdates );
335 * @param int $stage DeferredUpdates constant (PRESEND, POSTSEND, or ALL)
336 * @return DeferrableUpdate[]
339 public static function getPendingUpdates( $stage = self
::ALL
) {
341 if ( $stage === self
::ALL ||
$stage === self
::PRESEND
) {
342 $updates = array_merge( $updates, self
::$preSendUpdates );
344 if ( $stage === self
::ALL ||
$stage === self
::POSTSEND
) {
345 $updates = array_merge( $updates, self
::$postSendUpdates );
351 * Clear all pending updates without performing them. Generally, you don't
352 * want or need to call this. Unit tests need it though.
354 public static function clearPendingUpdates() {
355 self
::$preSendUpdates = [];
356 self
::$postSendUpdates = [];
360 * @return bool If a transaction round is active or connection is not ready for commit()
362 private static function areDatabaseTransactionsActive() {
363 $lbFactory = MediaWikiServices
::getInstance()->getDBLoadBalancerFactory();
364 if ( $lbFactory->hasTransactionRound() ) {
369 $lbFactory->forEachLB( function ( LoadBalancer
$lb ) use ( &$connsBusy ) {
370 $lb->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( &$connsBusy ) {
371 if ( $conn->writesOrCallbacksPending() ||
$conn->explicitTrxActive() ) {