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| 1 | <?php |
| 2 | /** |
| 3 | * This program is free software; you can redistribute it and/or modify |
| 4 | * it under the terms of the GNU General Public License as published by |
| 5 | * the Free Software Foundation; either version 2 of the License, or |
| 6 | * (at your option) any later version. |
| 7 | * |
| 8 | * This program is distributed in the hope that it will be useful, |
| 9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 11 | * GNU General Public License for more details. |
| 12 | * |
| 13 | * You should have received a copy of the GNU General Public License along |
| 14 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 15 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
| 16 | * http://www.gnu.org/copyleft/gpl.html |
| 17 | * |
| 18 | * @file |
| 19 | */ |
| 20 | |
| 21 | namespace MediaWiki\Deferred; |
| 22 | |
| 23 | use ErrorPageError; |
| 24 | use LogicException; |
| 25 | use MediaWiki\Logger\LoggerFactory; |
| 26 | use MWExceptionHandler; |
| 27 | use Throwable; |
| 28 | use Wikimedia\Rdbms\IDatabase; |
| 29 | use Wikimedia\ScopedCallback; |
| 30 | |
| 31 | /** |
| 32 | * Defer callable updates to run later in the PHP process |
| 33 | * |
| 34 | * This is a performance feature that enables MediaWiki to produce faster web responses. |
| 35 | * It allows you to postpone non-blocking work (e.g. work that does not change the web |
| 36 | * response) to after the HTTP response has been sent to the client (i.e. web browser). |
| 37 | * |
| 38 | * Once the response is finalized and sent to the browser, the webserver process stays |
| 39 | * for a little while longer (detached from the web request) to run your POSTSEND tasks. |
| 40 | * |
| 41 | * There is also a PRESEND option, which runs your task right before the finalized response |
| 42 | * is sent to the browser. This is for critical tasks that does need to block the response, |
| 43 | * but where you'd like to benefit from other DeferredUpdates features. Such as: |
| 44 | * |
| 45 | * - MergeableUpdate: batch updates from different components without coupling |
| 46 | * or awareness of each other. |
| 47 | * - Automatic cancellation: pass a IDatabase object (for any wiki or database) to |
| 48 | * DeferredUpdates::addCallableUpdate or AtomicSectionUpdate. |
| 49 | * - Reducing lock contention: if the response is likely to take several seconds |
| 50 | * (e.g. uploading a large file to FileBackend, or saving an edit to a large article) |
| 51 | * much of that work may overlap with a database transaction that is staying open for |
| 52 | * the entire duration. By moving contentious writes out to a PRESEND update, these |
| 53 | * get their own transaction (after the main one is committed), which give up some |
| 54 | * atomicity for improved throughput. |
| 55 | * |
| 56 | * ## Expectation and comparison to job queue |
| 57 | * |
| 58 | * When scheduling a POSTSEND via the DeferredUpdates system you can generally expect |
| 59 | * it to complete well before the client makes their next request. Updates runs directly after |
| 60 | * the web response is sent, from the same process on the same server. This unlike the JobQueue, |
| 61 | * where jobs may need to wait in line for some minutes or hours. |
| 62 | * |
| 63 | * If your update fails, this failure is not known to the client and gets no retry. For updates |
| 64 | * that need re-tries for system consistency or data integrity, it is recommended to implement |
| 65 | * it as a job instead and use JobQueueGroup::lazyPush. This has the caveat of being delayed |
| 66 | * by default, the same as any other job. |
| 67 | * |
| 68 | * A hybrid solution is available via the EnqueueableDataUpdate interface. By implementing |
| 69 | * this interface, you can queue your update via the DeferredUpdates first, and if it fails, |
| 70 | * the system will automatically catch this and queue it as a job instead. |
| 71 | * |
| 72 | * ## How it works during web requests |
| 73 | * |
| 74 | * 1. Your request route is executed (e.g. Action or SpecialPage class, or API). |
| 75 | * 2. Output is finalized and main database transaction is committed. |
| 76 | * 3. PRESEND updates run via DeferredUpdates::doUpdates. |
| 77 | * 5. The web response is sent to the browser. |
| 78 | * 6. POSTSEND updates run via DeferredUpdates::doUpdates. |
| 79 | * |
| 80 | * @see MediaWiki::preOutputCommit |
| 81 | * @see MediaWiki::restInPeace |
| 82 | * |
| 83 | * ## How it works for Maintenance scripts |
| 84 | * |
| 85 | * In CLI mode, no distinction is made between PRESEND and POSTSEND deferred updates, |
| 86 | * and the queue is periodically executed throughout the process. |
| 87 | * |
| 88 | * @see DeferredUpdates::tryOpportunisticExecute |
| 89 | * |
| 90 | * ## How it works internally |
| 91 | * |
| 92 | * Each update is added via DeferredUpdates::addUpdate and stored in either the PRESEND or |
| 93 | * POSTSEND queue. If an update gets queued while another update is already running, then |
| 94 | * we store in a "sub"-queue associated with the current update. This allows nested updates |
| 95 | * to be completed before other updates, which improves ordering for process caching. |
| 96 | * |
| 97 | * @since 1.19 |
| 98 | */ |
| 99 | class DeferredUpdates { |
| 100 | /** @var int Process all updates; in web requests, use only after flushing output buffer */ |
| 101 | public const ALL = 0; |
| 102 | /** @var int Specify/process updates that should run before flushing output buffer */ |
| 103 | public const PRESEND = 1; |
| 104 | /** @var int Specify/process updates that should run after flushing output buffer */ |
| 105 | public const POSTSEND = 2; |
| 106 | |
| 107 | /** @var int[] List of "defer until" queue stages that can be reached */ |
| 108 | public const STAGES = [ self::PRESEND, self::POSTSEND ]; |
| 109 | |
| 110 | /** @var DeferredUpdatesScopeStack|null Queue states based on recursion level */ |
| 111 | private static $scopeStack; |
| 112 | |
| 113 | /** |
| 114 | * @var int Nesting level for preventOpportunisticUpdates() |
| 115 | */ |
| 116 | private static $preventOpportunisticUpdates = 0; |
| 117 | |
| 118 | /** |
| 119 | * @return DeferredUpdatesScopeStack |
| 120 | */ |
| 121 | private static function getScopeStack(): DeferredUpdatesScopeStack { |
| 122 | self::$scopeStack ??= new DeferredUpdatesScopeMediaWikiStack(); |
| 123 | return self::$scopeStack; |
| 124 | } |
| 125 | |
| 126 | /** |
| 127 | * @param DeferredUpdatesScopeStack $scopeStack |
| 128 | * @internal Only for use in tests. |
| 129 | */ |
| 130 | public static function setScopeStack( DeferredUpdatesScopeStack $scopeStack ): void { |
| 131 | if ( !defined( 'MW_PHPUNIT_TEST' ) ) { |
| 132 | throw new LogicException( 'Cannot reconfigure DeferredUpdates outside tests' ); |
| 133 | } |
| 134 | self::$scopeStack = $scopeStack; |
| 135 | } |
| 136 | |
| 137 | /** |
| 138 | * Add an update to the pending update queue for execution at the appropriate time |
| 139 | * |
| 140 | * In CLI mode, callback magic will also be used to run updates when safe |
| 141 | * |
| 142 | * If an update is already in progress, then what happens to this update is as follows: |
| 143 | * - If it has a "defer until" stage at/before the actual run stage of the innermost |
| 144 | * in-progress update, then it will go into the sub-queue of that in-progress update. |
| 145 | * As soon as that update completes, MergeableUpdate instances in its sub-queue will be |
| 146 | * merged into the top-queues and the non-MergeableUpdate instances will be executed. |
| 147 | * This is done to better isolate updates from the failures of other updates and reduce |
| 148 | * the chance of race conditions caused by updates not fully seeing the intended changes |
| 149 | * of previously enqueued and executed updates. |
| 150 | * - If it has a "defer until" stage later than the actual run stage of the innermost |
| 151 | * in-progress update, then it will go into the normal top-queue for that stage. |
| 152 | * |
| 153 | * @param DeferrableUpdate $update Some object that implements doUpdate() |
| 154 | * @param int $stage One of (DeferredUpdates::PRESEND, DeferredUpdates::POSTSEND) |
| 155 | * @since 1.28 Added the $stage parameter |
| 156 | */ |
| 157 | public static function addUpdate( DeferrableUpdate $update, $stage = self::POSTSEND ) { |
| 158 | self::getScopeStack()->current()->addUpdate( $update, $stage ); |
| 159 | self::tryOpportunisticExecute(); |
| 160 | } |
| 161 | |
| 162 | /** |
| 163 | * Add an update to the pending update queue that invokes the specified callback when run |
| 164 | * |
| 165 | * @param callable $callable One of the following: |
| 166 | * - A Closure callback that takes the caller name as its argument |
| 167 | * - A non-Closure callback that takes no arguments |
| 168 | * @param int $stage One of (DeferredUpdates::PRESEND, DeferredUpdates::POSTSEND) |
| 169 | * @param IDatabase|IDatabase[] $dependeeDbws DB handles which might have pending writes |
| 170 | * upon which this update depends. If any of the handles already has an open transaction, |
| 171 | * a rollback thereof will cause this update to be cancelled (if it has not already run). |
| 172 | * [optional] (since 1.28) |
| 173 | * @since 1.27 Added $stage parameter |
| 174 | * @since 1.28 Added the $dbw parameter |
| 175 | * @since 1.43 Closures are now given the caller name parameter |
| 176 | */ |
| 177 | public static function addCallableUpdate( |
| 178 | $callable, |
| 179 | $stage = self::POSTSEND, |
| 180 | $dependeeDbws = [] |
| 181 | ) { |
| 182 | self::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dependeeDbws ), $stage ); |
| 183 | } |
| 184 | |
| 185 | /** |
| 186 | * Run an update, and, if an error was thrown, catch/log it and enqueue the update as |
| 187 | * a job in the job queue system if possible (e.g. implements EnqueueableDataUpdate) |
| 188 | * |
| 189 | * @param DeferrableUpdate $update |
| 190 | * @return Throwable|null |
| 191 | */ |
| 192 | private static function run( DeferrableUpdate $update ): ?Throwable { |
| 193 | $logger = LoggerFactory::getInstance( 'DeferredUpdates' ); |
| 194 | |
| 195 | $type = get_class( $update ) |
| 196 | . ( $update instanceof DeferrableCallback ? '_' . $update->getOrigin() : '' ); |
| 197 | $updateId = spl_object_id( $update ); |
| 198 | $logger->debug( "DeferredUpdates::run: started $type #{updateId}", [ 'updateId' => $updateId ] ); |
| 199 | |
| 200 | $updateException = null; |
| 201 | |
| 202 | $startTime = microtime( true ); |
| 203 | try { |
| 204 | self::attemptUpdate( $update ); |
| 205 | } catch ( Throwable $updateException ) { |
| 206 | MWExceptionHandler::logException( $updateException ); |
| 207 | $logger->error( |
| 208 | "Deferred update '{deferred_type}' failed to run.", |
| 209 | [ |
| 210 | 'deferred_type' => $type, |
| 211 | 'exception' => $updateException, |
| 212 | ] |
| 213 | ); |
| 214 | self::getScopeStack()->onRunUpdateFailed( $update ); |
| 215 | } finally { |
| 216 | $walltime = microtime( true ) - $startTime; |
| 217 | $logger->debug( "DeferredUpdates::run: ended $type #{updateId}, processing time: {walltime}", [ |
| 218 | 'updateId' => $updateId, |
| 219 | 'walltime' => $walltime, |
| 220 | ] ); |
| 221 | } |
| 222 | |
| 223 | // Try to push the update as a job so it can run later if possible |
| 224 | if ( $updateException && $update instanceof EnqueueableDataUpdate ) { |
| 225 | try { |
| 226 | self::getScopeStack()->queueDataUpdate( $update ); |
| 227 | } catch ( Throwable $jobException ) { |
| 228 | MWExceptionHandler::logException( $jobException ); |
| 229 | $logger->error( |
| 230 | "Deferred update '{deferred_type}' failed to enqueue as a job.", |
| 231 | [ |
| 232 | 'deferred_type' => $type, |
| 233 | 'exception' => $jobException, |
| 234 | ] |
| 235 | ); |
| 236 | self::getScopeStack()->onRunUpdateFailed( $update ); |
| 237 | } |
| 238 | } |
| 239 | |
| 240 | return $updateException; |
| 241 | } |
| 242 | |
| 243 | /** |
| 244 | * Consume and execute all pending updates |
| 245 | * |
| 246 | * Note that it is rarely the case that this method should be called outside of a few |
| 247 | * select entry points. For simplicity, that kind of recursion is discouraged. Recursion |
| 248 | * cannot happen if an explicit transaction round is active, which limits usage to updates |
| 249 | * with TRX_ROUND_ABSENT that do not leave open any transactions round of their own during |
| 250 | * the call to this method. |
| 251 | * |
| 252 | * In the less-common case of this being called within an in-progress DeferrableUpdate, |
| 253 | * this will not see any top-queue updates (since they were consumed and are being run |
| 254 | * inside an outer execution loop). In that case, it will instead operate on the sub-queue |
| 255 | * of the innermost in-progress update on the stack. |
| 256 | * |
| 257 | * @internal For use by MediaWiki, Maintenance, JobRunner, JobExecutor |
| 258 | * @param int $stage Which updates to process. One of |
| 259 | * (DeferredUpdates::PRESEND, DeferredUpdates::POSTSEND, DeferredUpdates::ALL) |
| 260 | */ |
| 261 | public static function doUpdates( $stage = self::ALL ) { |
| 262 | /** @var ErrorPageError $guiError First presentable client-level error thrown */ |
| 263 | $guiError = null; |
| 264 | /** @var Throwable $exception First of any error thrown */ |
| 265 | $exception = null; |
| 266 | |
| 267 | $scope = self::getScopeStack()->current(); |
| 268 | |
| 269 | // T249069: recursion is not possible once explicit transaction rounds are involved |
| 270 | $activeUpdate = $scope->getActiveUpdate(); |
| 271 | if ( $activeUpdate ) { |
| 272 | $class = get_class( $activeUpdate ); |
| 273 | if ( !( $activeUpdate instanceof TransactionRoundAwareUpdate ) ) { |
| 274 | throw new LogicException( |
| 275 | __METHOD__ . ": reached from $class, which is not TransactionRoundAwareUpdate" |
| 276 | ); |
| 277 | } |
| 278 | if ( $activeUpdate->getTransactionRoundRequirement() !== $activeUpdate::TRX_ROUND_ABSENT ) { |
| 279 | throw new LogicException( |
| 280 | __METHOD__ . ": reached from $class, which does not specify TRX_ROUND_ABSENT" |
| 281 | ); |
| 282 | } |
| 283 | } |
| 284 | |
| 285 | $scope->processUpdates( |
| 286 | $stage, |
| 287 | static function ( DeferrableUpdate $update, $activeStage ) use ( &$guiError, &$exception ) { |
| 288 | $scopeStack = self::getScopeStack(); |
| 289 | $childScope = $scopeStack->descend( $activeStage, $update ); |
| 290 | try { |
| 291 | $e = self::run( $update ); |
| 292 | $guiError = $guiError ?: ( $e instanceof ErrorPageError ? $e : null ); |
| 293 | $exception = $exception ?: $e; |
| 294 | // Any addUpdate() calls between descend() and ascend() used the sub-queue. |
| 295 | // In rare cases, DeferrableUpdate::doUpdates() will process them by calling |
| 296 | // doUpdates() itself. In any case, process remaining updates in the subqueue. |
| 297 | // them, enqueueing them, or transferring them to the parent scope |
| 298 | // queues as appropriate... |
| 299 | $childScope->processUpdates( |
| 300 | $activeStage, |
| 301 | static function ( DeferrableUpdate $sub ) use ( &$guiError, &$exception ) { |
| 302 | $e = self::run( $sub ); |
| 303 | $guiError = $guiError ?: ( $e instanceof ErrorPageError ? $e : null ); |
| 304 | $exception = $exception ?: $e; |
| 305 | } |
| 306 | ); |
| 307 | } finally { |
| 308 | $scopeStack->ascend(); |
| 309 | } |
| 310 | } |
| 311 | ); |
| 312 | |
| 313 | // VW-style hack to work around T190178, so we can make sure |
| 314 | // PageMetaDataUpdater doesn't throw exceptions. |
| 315 | if ( $exception && defined( 'MW_PHPUNIT_TEST' ) ) { |
| 316 | throw $exception; |
| 317 | } |
| 318 | |
| 319 | // Throw the first of any GUI errors as long as the context is HTTP pre-send. However, |
| 320 | // callers should check permissions *before* enqueueing updates. If the main transaction |
| 321 | // round actions succeed but some deferred updates fail due to permissions errors then |
| 322 | // there is a risk that some secondary data was not properly updated. |
| 323 | if ( $guiError && $stage === self::PRESEND && !headers_sent() ) { |
| 324 | throw $guiError; |
| 325 | } |
| 326 | } |
| 327 | |
| 328 | /** |
| 329 | * Consume and execute pending updates now if possible, instead of waiting. |
| 330 | * |
| 331 | * In web requests, updates are always deferred until the end of the request. |
| 332 | * |
| 333 | * In CLI mode, updates run earlier and more often. This is important for long-running |
| 334 | * Maintenance scripts that would otherwise grow an excessively large queue, which increases |
| 335 | * memory use, and risks losing all updates if the script ends early or crashes. |
| 336 | * |
| 337 | * The folllowing conditions are required for updates to run early in CLI mode: |
| 338 | * |
| 339 | * - No update is already in progress (ensure linear flow, recursion guard). |
| 340 | * - LBFactory indicates that we don't have any "busy" database connections, i.e. |
| 341 | * there are no pending writes or otherwise active and uncommitted transactions, |
| 342 | * except if the transaction is empty and merely used for primary DB read queries, |
| 343 | * in which case the transaction (and its repeatable-read snapshot) can be safely flushed. |
| 344 | * |
| 345 | * How this works: |
| 346 | * |
| 347 | * - When a maintenance script commits a change or waits for replication, such as |
| 348 | * via IConnectionProvider::commitAndWaitForReplication, then ILBFactory calls |
| 349 | * tryOpportunisticExecute(). This is injected via MWLBFactory::applyGlobalState. |
| 350 | * |
| 351 | * - For maintenance scripts that don't do much with the database, we also call |
| 352 | * tryOpportunisticExecute() after every addUpdate() call. |
| 353 | * |
| 354 | * - Upon the completion of Maintenance::execute() via Maintenance::shutdown(), |
| 355 | * any remaining updates are run. |
| 356 | * |
| 357 | * Note that this method runs both PRESEND and POSTSEND updates and thus should not be called |
| 358 | * during web requests. It is only intended for long-running Maintenance scripts. |
| 359 | * |
| 360 | * @internal For use by Maintenance |
| 361 | * @since 1.28 |
| 362 | * @return bool Whether updates were allowed to run |
| 363 | */ |
| 364 | public static function tryOpportunisticExecute(): bool { |
| 365 | // Leave execution up to the current loop if an update is already in progress |
| 366 | // or if updates are explicitly disabled |
| 367 | if ( self::getRecursiveExecutionStackDepth() |
| 368 | || self::$preventOpportunisticUpdates |
| 369 | ) { |
| 370 | return false; |
| 371 | } |
| 372 | |
| 373 | if ( self::getScopeStack()->allowOpportunisticUpdates() ) { |
| 374 | self::doUpdates( self::ALL ); |
| 375 | return true; |
| 376 | } |
| 377 | |
| 378 | return false; |
| 379 | } |
| 380 | |
| 381 | /** |
| 382 | * Prevent opportunistic updates until the returned ScopedCallback is |
| 383 | * consumed. |
| 384 | * |
| 385 | * @return ScopedCallback |
| 386 | */ |
| 387 | public static function preventOpportunisticUpdates() { |
| 388 | self::$preventOpportunisticUpdates++; |
| 389 | return new ScopedCallback( static function () { |
| 390 | self::$preventOpportunisticUpdates--; |
| 391 | } ); |
| 392 | } |
| 393 | |
| 394 | /** |
| 395 | * Get the number of pending updates for the current execution context |
| 396 | * |
| 397 | * If an update is in progress, then this operates on the sub-queues of the |
| 398 | * innermost in-progress update. Otherwise, it acts on the top-queues. |
| 399 | * |
| 400 | * @return int |
| 401 | * @since 1.28 |
| 402 | */ |
| 403 | public static function pendingUpdatesCount() { |
| 404 | return self::getScopeStack()->current()->pendingUpdatesCount(); |
| 405 | } |
| 406 | |
| 407 | /** |
| 408 | * Get a list of the pending updates for the current execution context |
| 409 | * |
| 410 | * If an update is in progress, then this operates on the sub-queues of the |
| 411 | * innermost in-progress update. Otherwise, it acts on the top-queues. |
| 412 | * |
| 413 | * @param int $stage Look for updates with this "defer until" stage. One of |
| 414 | * (DeferredUpdates::PRESEND, DeferredUpdates::POSTSEND, DeferredUpdates::ALL) |
| 415 | * @return DeferrableUpdate[] |
| 416 | * @internal This method should only be used for unit tests |
| 417 | * @since 1.29 |
| 418 | */ |
| 419 | public static function getPendingUpdates( $stage = self::ALL ) { |
| 420 | return self::getScopeStack()->current()->getPendingUpdates( $stage ); |
| 421 | } |
| 422 | |
| 423 | /** |
| 424 | * Cancel all pending updates for the current execution context |
| 425 | * |
| 426 | * If an update is in progress, then this operates on the sub-queues of the |
| 427 | * innermost in-progress update. Otherwise, it acts on the top-queues. |
| 428 | * |
| 429 | * @internal This method should only be used for unit tests |
| 430 | */ |
| 431 | public static function clearPendingUpdates() { |
| 432 | self::getScopeStack()->current()->clearPendingUpdates(); |
| 433 | } |
| 434 | |
| 435 | /** |
| 436 | * Get the number of in-progress calls to DeferredUpdates::doUpdates() |
| 437 | * |
| 438 | * @return int |
| 439 | * @internal This method should only be used for unit tests |
| 440 | */ |
| 441 | public static function getRecursiveExecutionStackDepth() { |
| 442 | return self::getScopeStack()->getRecursiveDepth(); |
| 443 | } |
| 444 | |
| 445 | /** |
| 446 | * Attempt to run an update with the appropriate transaction round state if needed |
| 447 | * |
| 448 | * It is allowed for a DeferredUpdate to directly execute one or more other DeferredUpdate |
| 449 | * instances without queueing them by calling this method. In that case, the outer update |
| 450 | * must use TransactionRoundAwareUpdate::TRX_ROUND_ABSENT, e.g. by extending |
| 451 | * TransactionRoundDefiningUpdate, so that this method can give each update its own |
| 452 | * transaction round. |
| 453 | * |
| 454 | * @param DeferrableUpdate $update |
| 455 | * @since 1.34 |
| 456 | */ |
| 457 | public static function attemptUpdate( DeferrableUpdate $update ) { |
| 458 | self::getScopeStack()->onRunUpdateStart( $update ); |
| 459 | |
| 460 | $update->doUpdate(); |
| 461 | |
| 462 | self::getScopeStack()->onRunUpdateEnd( $update ); |
| 463 | } |
| 464 | } |
| 465 | |
| 466 | /** @deprecated class alias since 1.42 */ |
| 467 | class_alias( DeferredUpdates::class, 'DeferredUpdates' ); |