JobQueue.php
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JobQueue.php
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	<?php
	/**
	* This program 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 2 of the License, or
	* (at your option) any later version.
	*
	* This program 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 this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	* http://www.gnu.org/copyleft/gpl.html
	*
	* @file
	*/

	namespace MediaWiki\JobQueue;

	use ArrayIterator;
	use Exception;
	use MediaWiki\JobQueue\Exceptions\JobQueueError;
	use MediaWiki\JobQueue\Exceptions\JobQueueReadOnlyError;
	use MediaWiki\JobQueue\Jobs\DuplicateJob;
	use MediaWiki\MediaWikiServices;
	use Wikimedia\ObjectCache\WANObjectCache;
	use Wikimedia\RequestTimeout\TimeoutException;
	use Wikimedia\Stats\StatsFactory;
	use Wikimedia\UUID\GlobalIdGenerator;

	/**
	* @defgroup JobQueue JobQueue
	*
	*
	* See [the architecture doc](@ref jobqueuearch) for more information.
	*/

	/**
	* Base class for queueing and running background jobs from a storage backend.
	*
	* See [the architecture doc](@ref jobqueuearch) for more information.
	*
	* @ingroup JobQueue
	* @since 1.21
	* @stable to extend
	*/
	abstract class JobQueue {
	/** @var string DB domain ID */
	protected $domain;
	/** @var string Job type */
	protected $type;
	/** @var string Job priority for pop() */
	protected $order;
	/** @var int Time to live in seconds */
	protected $claimTTL;
	/** @var int Maximum number of times to try a job */
	protected $maxTries;
	/** @var string\|false Read only rationale (or false if r/w) */
	protected $readOnlyReason;
	/** @var StatsFactory */
	protected $stats;
	/** @var GlobalIdGenerator */
	protected $idGenerator;

	/** @var WANObjectCache */
	protected $wanCache;

	/** @var bool */
	protected $typeAgnostic;

	private JobFactory $jobFactory;

	/* Bit flag for "all-or-nothing" job insertions */
	protected const QOS_ATOMIC = 1;

	/* Seconds to remember root jobs (28 days) */
	protected const ROOTJOB_TTL = 28 * 24 * 3600;

	/**
	* @stable to call
	*
	* @param array $params
	* - type : A job type, 'default' if typeAgnostic is set
	* - domain : A DB domain ID
	* - idGenerator : A GlobalIdGenerator instance.
	* - wanCache : An instance of WANObjectCache to use for caching [default: none]
	* - stats : An instance of StatsFactory [default: none]
	* - claimTTL : Seconds a job can be claimed for exclusive execution [default: forever]
	* - maxTries : Total times a job can be tried, assuming claims expire [default: 3]
	* - order : Queue order, one of ("fifo", "timestamp", "random") [default: variable]
	* - readOnlyReason : Mark the queue as read-only with this reason [default: false]
	* - typeAgnostic : If the jobqueue should operate agnostic to the job types
	* @throws JobQueueError
	*
	*/
	protected function __construct( array $params ) {
	$this->domain = $params['domain'] ?? $params['wiki']; // b/c
	$this->type = $params['type'];
	$this->claimTTL = $params['claimTTL'] ?? 0;
	$this->maxTries = $params['maxTries'] ?? 3;
	if ( isset( $params['order'] ) && $params['order'] !== 'any' ) {
	$this->order = $params['order'];
	} else {
	$this->order = $this->optimalOrder();
	}
	if ( !in_array( $this->order, $this->supportedOrders() ) ) {
	throw new JobQueueError( __CLASS__ . " does not support '{$this->order}' order." );
	}
	$this->readOnlyReason = $params['readOnlyReason'] ?? false;
	$this->stats = $params['stats'] ?? StatsFactory::newNull();
	$this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
	$this->idGenerator = $params['idGenerator'];
	if ( ( $params['typeAgnostic'] ?? false ) && !$this->supportsTypeAgnostic() ) {
	throw new JobQueueError( __CLASS__ . " does not support type agnostic queues." );
	}
	$this->typeAgnostic = ( $params['typeAgnostic'] ?? false );
	if ( $this->typeAgnostic ) {
	$this->type = 'default';
	}

	$this->jobFactory = MediaWikiServices::getInstance()->getJobFactory();
	}

	/**
	* Get a job queue object of the specified type.
	* $params includes:
	* - class : What job class to use (determines job type)
	* - domain : Database domain ID of the wiki the jobs are for (defaults to current wiki)
	* - type : The name of the job types this queue handles
	* - order : Order that pop() selects jobs, one of "fifo", "timestamp" or "random".
	* If "fifo" is used, the queue will effectively be FIFO. Note that job
	* completion will not appear to be exactly FIFO if there are multiple
	* job runners since jobs can take different times to finish once popped.
	* If "timestamp" is used, the queue will at least be loosely ordered
	* by timestamp, allowing for some jobs to be popped off out of order.
	* If "random" is used, pop() will pick jobs in random order.
	* Note that it may only be weakly random (e.g. a lottery of the oldest X).
	* If "any" is chosen, the queue will use whatever order is the fastest.
	* This might be useful for improving concurrency for job acquisition.
	* - claimTTL : If supported, the queue will recycle jobs that have been popped
	* but not acknowledged as completed after this many seconds. Recycling
	* of jobs simply means re-inserting them into the queue. Jobs can be
	* attempted up to three times before being discarded.
	* - readOnlyReason : Set this to a string to make the queue read-only. [optional]
	* - idGenerator : A GlobalIdGenerator instance.
	* - stats : A StatsFactory. [optional]
	*
	* Queue classes should throw an exception if they do not support the options given.
	*
	* @param array $params
	* @return JobQueue
	* @throws JobQueueError
	*/
	final public static function factory( array $params ) {
	$class = $params['class'];
	if ( !class_exists( $class ) ) {
	throw new JobQueueError( "Invalid job queue class '$class'." );
	}

	$obj = new $class( $params );
	if ( !( $obj instanceof self ) ) {
	throw new JobQueueError( "Class '$class' is not a " . __CLASS__ . " class." );
	}

	return $obj;
	}

	/**
	* @return string Database domain ID
	*/
	final public function getDomain() {
	return $this->domain;
	}

	/**
	* @return string Job type that this queue handles
	*/
	final public function getType() {
	return $this->type;
	}

	/**
	* @return string One of (random, timestamp, fifo, undefined)
	*/
	final public function getOrder() {
	return $this->order;
	}

	/**
	* Get the allowed queue orders for configuration validation
	*
	* @return array Subset of (random, timestamp, fifo, undefined)
	*/
	abstract protected function supportedOrders();

	/**
	* Get the default queue order to use if configuration does not specify one
	*
	* @return string One of (random, timestamp, fifo, undefined)
	*/
	abstract protected function optimalOrder();

	/**
	* Find out if delayed jobs are supported for configuration validation
	*
	* @stable to override
	* @return bool Whether delayed jobs are supported
	*/
	protected function supportsDelayedJobs() {
	return false; // not implemented
	}

	/**
	* @return bool Whether delayed jobs are enabled
	* @since 1.22
	*/
	final public function delayedJobsEnabled() {
	return $this->supportsDelayedJobs();
	}

	/**
	* @return string\|false Read-only rational or false if r/w
	* @since 1.27
	*/
	public function getReadOnlyReason() {
	return $this->readOnlyReason;
	}

	/**
	* Quickly check if the queue has no available (unacquired, non-delayed) jobs.
	* Queue classes should use caching if they are any slower without memcached.
	*
	* If caching is used, this might return false when there are actually no jobs.
	* If pop() is called and returns false then it should correct the cache. Also,
	* calling flushCaches() first prevents this. However, this effect is typically
	* not distinguishable from the race condition between isEmpty() and pop().
	*
	* @return bool
	* @throws JobQueueError
	*/
	final public function isEmpty() {
	$res = $this->doIsEmpty();

	return $res;
	}

	/**
	* @see JobQueue::isEmpty()
	* @return bool
	*/
	abstract protected function doIsEmpty();

	/**
	* Get the number of available (unacquired, non-delayed) jobs in the queue.
	* Queue classes should use caching if they are any slower without memcached.
	*
	* If caching is used, this number might be out of date for a minute.
	*
	* @return int
	* @throws JobQueueError
	*/
	final public function getSize() {
	$res = $this->doGetSize();

	return $res;
	}

	/**
	* @see JobQueue::getSize()
	* @return int
	*/
	abstract protected function doGetSize();

	/**
	* Get the number of acquired jobs (these are temporarily out of the queue).
	* Queue classes should use caching if they are any slower without memcached.
	*
	* If caching is used, this number might be out of date for a minute.
	*
	* @return int
	* @throws JobQueueError
	*/
	final public function getAcquiredCount() {
	$res = $this->doGetAcquiredCount();

	return $res;
	}

	/**
	* @see JobQueue::getAcquiredCount()
	* @return int
	*/
	abstract protected function doGetAcquiredCount();

	/**
	* Get the number of delayed jobs (these are temporarily out of the queue).
	* Queue classes should use caching if they are any slower without memcached.
	*
	* If caching is used, this number might be out of date for a minute.
	*
	* @return int
	* @throws JobQueueError
	* @since 1.22
	*/
	final public function getDelayedCount() {
	$res = $this->doGetDelayedCount();

	return $res;
	}

	/**
	* @stable to override
	* @see JobQueue::getDelayedCount()
	* @return int
	*/
	protected function doGetDelayedCount() {
	return 0; // not implemented
	}

	/**
	* Get the number of acquired jobs that can no longer be attempted.
	* Queue classes should use caching if they are any slower without memcached.
	*
	* If caching is used, this number might be out of date for a minute.
	*
	* @return int
	* @throws JobQueueError
	*/
	final public function getAbandonedCount() {
	$res = $this->doGetAbandonedCount();

	return $res;
	}

	/**
	* @stable to override
	* @see JobQueue::getAbandonedCount()
	* @return int
	*/
	protected function doGetAbandonedCount() {
	return 0; // not implemented
	}

	/**
	* Push one or more jobs into the queue.
	* This does not require $wgJobClasses to be set for the given job type.
	* Outside callers should use JobQueueGroup::push() instead of this function.
	*
	* @param IJobSpecification\|IJobSpecification[] $jobs
	* @param int $flags Bitfield (supports JobQueue::QOS_ATOMIC)
	* @return void
	* @throws JobQueueError
	*/
	final public function push( $jobs, $flags = 0 ) {
	$jobs = is_array( $jobs ) ? $jobs : [ $jobs ];
	$this->batchPush( $jobs, $flags );
	}

	/**
	* Push a batch of jobs into the queue.
	* This does not require $wgJobClasses to be set for the given job type.
	* Outside callers should use JobQueueGroup::push() instead of this function.
	*
	* @param IJobSpecification[] $jobs
	* @param int $flags Bitfield (supports JobQueue::QOS_ATOMIC)
	* @return void
	* @throws JobQueueError
	*/
	final public function batchPush( array $jobs, $flags = 0 ) {
	$this->assertNotReadOnly();

	if ( $jobs === [] ) {
	return; // nothing to do
	}

	foreach ( $jobs as $job ) {
	$this->assertMatchingJobType( $job );
	if ( $job->getReleaseTimestamp() && !$this->supportsDelayedJobs() ) {
	throw new JobQueueError(
	"Got delayed '{$job->getType()}' job; delays are not supported." );
	}
	}

	$this->doBatchPush( $jobs, $flags );

	foreach ( $jobs as $job ) {
	if ( $job->isRootJob() ) {
	$this->deduplicateRootJob( $job );
	}
	}
	}

	/**
	* @see JobQueue::batchPush()
	* @param IJobSpecification[] $jobs
	* @param int $flags
	*/
	abstract protected function doBatchPush( array $jobs, $flags );

	/**
	* Pop a job off of the queue.
	* This requires $wgJobClasses to be set for the given job type.
	* Outside callers should use JobQueueGroup::pop() instead of this function.
	*
	* @throws JobQueueError
	* @return RunnableJob\|false Returns false if there are no jobs
	*/
	final public function pop() {
	$this->assertNotReadOnly();

	$job = $this->doPop();

	// Flag this job as an old duplicate based on its "root" job...
	try {
	if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
	$this->incrStats( 'dupe_pops', $job->getType() );
	$job = DuplicateJob::newFromJob( $job ); // convert to a no-op
	}
	} catch ( TimeoutException $e ) {
	throw $e;
	} catch ( Exception $e ) {
	// don't lose jobs over this
	}

	return $job;
	}

	/**
	* @see JobQueue::pop()
	* @return RunnableJob\|false
	*/
	abstract protected function doPop();

	/**
	* Acknowledge that a job was completed.
	*
	* This does nothing for certain queue classes or if "claimTTL" is not set.
	* Outside callers should use JobQueueGroup::ack() instead of this function.
	*
	* @param RunnableJob $job
	* @return void
	* @throws JobQueueError
	*/
	final public function ack( RunnableJob $job ) {
	$this->assertNotReadOnly();
	$this->assertMatchingJobType( $job );

	$this->doAck( $job );
	}

	/**
	* @see JobQueue::ack()
	* @param RunnableJob $job
	*/
	abstract protected function doAck( RunnableJob $job );

	/**
	* Register the "root job" of a given job into the queue for de-duplication.
	* This should only be called right after all the new jobs have been inserted.
	* This is used to turn older, duplicate, job entries into no-ops. The root job
	* information will remain in the registry until it simply falls out of cache.
	*
	* This requires that $job has two special fields in the "params" array:
	* - rootJobSignature : hash (e.g. SHA1) that identifies the task
	* - rootJobTimestamp : TS_MW timestamp of this instance of the task
	*
	* A "root job" is a conceptual job that consist of potentially many smaller jobs
	* that are actually inserted into the queue. For example, "refreshLinks" jobs are
	* spawned when a template is edited. One can think of the task as "update links
	* of pages that use template X" and an instance of that task as a "root job".
	* However, what actually goes into the queue are range and leaf job subtypes.
	* Since these jobs include things like page ID ranges and DB primary positions,
	* and can morph into smaller jobs recursively, simple duplicate detection
	* for individual jobs being identical (like that of job_sha1) is not useful.
	*
	* In the case of "refreshLinks", if these jobs are still in the queue when the template
	* is edited again, we want all of these old refreshLinks jobs for that template to become
	* no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
	* Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
	* previous "root job" for the same task of "update links of pages that use template X".
	*
	* This does nothing for certain queue classes.
	*
	* @internal For use within JobQueue only
	* @param IJobSpecification $job
	* @throws JobQueueError
	* @return bool
	*/
	final public function deduplicateRootJob( IJobSpecification $job ) {
	$this->assertNotReadOnly();
	$this->assertMatchingJobType( $job );

	return $this->doDeduplicateRootJob( $job );
	}

	/**
	* @stable to override
	* @see JobQueue::deduplicateRootJob()
	* @param IJobSpecification $job
	* @throws JobQueueError
	* @return bool
	*/
	protected function doDeduplicateRootJob( IJobSpecification $job ) {
	$params = $job->hasRootJobParams() ? $job->getRootJobParams() : null;
	if ( !$params ) {
	throw new JobQueueError( "Cannot register root job; missing parameters." );
	}

	$key = $this->getRootJobCacheKey( $params['rootJobSignature'], $job->getType() );
	// Callers should call JobQueueGroup::push() before this method so that if the
	// insert fails, the de-duplication registration will be aborted. Having only the
	// de-duplication registration succeed would cause jobs to become no-ops without
	// any actual jobs that made them redundant.
	$timestamp = $this->wanCache->get( $key ); // last known timestamp of such a root job
	if ( $timestamp !== false && $timestamp >= $params['rootJobTimestamp'] ) {
	return true; // a newer version of this root job was enqueued
	}

	// Update the timestamp of the last root job started at the location...
	return $this->wanCache->set( $key, $params['rootJobTimestamp'], self::ROOTJOB_TTL );
	}

	/**
	* Check if the "root" job of a given job has been superseded by a newer one
	*
	* @param IJobSpecification $job
	* @throws JobQueueError
	* @return bool
	*/
	final protected function isRootJobOldDuplicate( IJobSpecification $job ) {
	$this->assertMatchingJobType( $job );

	return $this->doIsRootJobOldDuplicate( $job );
	}

	/**
	* @stable to override
	* @see JobQueue::isRootJobOldDuplicate()
	* @param IJobSpecification $job
	* @return bool
	*/
	protected function doIsRootJobOldDuplicate( IJobSpecification $job ) {
	$params = $job->hasRootJobParams() ? $job->getRootJobParams() : null;
	if ( !$params ) {
	return false; // job has no de-duplication info
	}

	$key = $this->getRootJobCacheKey( $params['rootJobSignature'], $job->getType() );
	// Get the last time this root job was enqueued
	$timestamp = $this->wanCache->get( $key );
	if ( $timestamp === false \|\| $params['rootJobTimestamp'] > $timestamp ) {
	// Update the timestamp of the last known root job started at the location...
	$this->wanCache->set( $key, $params['rootJobTimestamp'], self::ROOTJOB_TTL );
	}

	// Check if a new root job was started at the location after this one's...
	return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
	}

	/**
	* @param string $signature Hash identifier of the root job
	* @param string $type job type
	* @return string
	*/
	protected function getRootJobCacheKey( $signature, $type ) {
	return $this->wanCache->makeGlobalKey(
	'jobqueue',
	$this->domain,
	$type,
	'rootjob',
	$signature
	);
	}

	/**
	* Delete all unclaimed and delayed jobs from the queue
	*
	* @throws JobQueueError
	* @since 1.22
	* @return void
	*/
	final public function delete() {
	$this->assertNotReadOnly();

	$this->doDelete();
	}

	/**
	* @stable to override
	* @see JobQueue::delete()
	* @throws JobQueueError
	*/
	protected function doDelete() {
	throw new JobQueueError( "This method is not implemented." );
	}

	/**
	* Wait for any replica DBs or backup servers to catch up.
	*
	* This does nothing for certain queue classes.
	*
	* @return void
	* @throws JobQueueError
	*/
	final public function waitForBackups() {
	$this->doWaitForBackups();
	}

	/**
	* @stable to override
	* @see JobQueue::waitForBackups()
	* @return void
	*/
	protected function doWaitForBackups() {
	}

	/**
	* Clear any process and persistent caches
	*
	* @return void
	*/
	final public function flushCaches() {
	$this->doFlushCaches();
	}

	/**
	* @stable to override
	* @see JobQueue::flushCaches()
	* @return void
	*/
	protected function doFlushCaches() {
	}

	/**
	* Get an iterator to traverse over all available jobs in this queue.
	* This does not include jobs that are currently acquired or delayed.
	* Note: results may be stale if the queue is concurrently modified.
	*
	* @return \Iterator<RunnableJob>
	* @throws JobQueueError
	*/
	abstract public function getAllQueuedJobs();

	/**
	* Get an iterator to traverse over all delayed jobs in this queue.
	* Note: results may be stale if the queue is concurrently modified.
	*
	* @stable to override
	* @return \Iterator<RunnableJob>
	* @throws JobQueueError
	* @since 1.22
	*/
	public function getAllDelayedJobs() {
	return new ArrayIterator( [] ); // not implemented
	}

	/**
	* Get an iterator to traverse over all claimed jobs in this queue
	*
	* Callers should be quick to iterator over it or few results
	* will be returned due to jobs being acknowledged and deleted
	*
	* @stable to override
	* @return \Iterator<RunnableJob>
	* @throws JobQueueError
	* @since 1.26
	*/
	public function getAllAcquiredJobs() {
	return new ArrayIterator( [] ); // not implemented
	}

	/**
	* Get an iterator to traverse over all abandoned jobs in this queue
	*
	* @stable to override
	* @return \Iterator<RunnableJob>
	* @throws JobQueueError
	* @since 1.25
	*/
	public function getAllAbandonedJobs() {
	return new ArrayIterator( [] ); // not implemented
	}

	/**
	* Do not use this function outside of JobQueue/JobQueueGroup
	*
	* @stable to override
	* @return string\|null
	* @since 1.22
	*/
	public function getCoalesceLocationInternal() {
	return null;
	}

	/**
	* Check whether each of the given queues are empty.
	* This is used for batching checks for queues stored at the same place.
	*
	* @param array $types List of queues types
	* @return array\|null (list of non-empty queue types) or null if unsupported
	* @throws JobQueueError
	* @since 1.22
	*/
	final public function getSiblingQueuesWithJobs( array $types ) {
	return $this->doGetSiblingQueuesWithJobs( $types );
	}

	/**
	* @stable to override
	* @see JobQueue::getSiblingQueuesWithJobs()
	* @param array $types List of queues types
	* @return array\|null (list of queue types) or null if unsupported
	*/
	protected function doGetSiblingQueuesWithJobs( array $types ) {
	return null; // not supported
	}

	/**
	* Check the size of each of the given queues.
	* For queues not served by the same store as this one, 0 is returned.
	* This is used for batching checks for queues stored at the same place.
	*
	* @param array $types List of queues types
	* @return array\|null (job type => whether queue is empty) or null if unsupported
	* @throws JobQueueError
	* @since 1.22
	*/
	final public function getSiblingQueueSizes( array $types ) {
	return $this->doGetSiblingQueueSizes( $types );
	}

	/**
	* @stable to override
	* @see JobQueue::getSiblingQueuesSize()
	* @param array $types List of queues types
	* @return array\|null (list of queue types) or null if unsupported
	*/
	protected function doGetSiblingQueueSizes( array $types ) {
	return null; // not supported
	}

	/**
	* @param string $command
	* @param array $params
	* @return Job
	*/
	protected function factoryJob( $command, $params ) {
	return $this->jobFactory->newJob( $command, $params );
	}

	/**
	* @throws JobQueueReadOnlyError
	*/
	protected function assertNotReadOnly() {
	if ( $this->readOnlyReason !== false ) {
	throw new JobQueueReadOnlyError( "Job queue is read-only: {$this->readOnlyReason}" );
	}
	}

	/**
	* @param IJobSpecification $job
	* @throws JobQueueError
	*/
	private function assertMatchingJobType( IJobSpecification $job ) {
	if ( $this->typeAgnostic ) {
	return;
	}
	if ( $job->getType() !== $this->type ) {
	throw new JobQueueError( "Got '{$job->getType()}' job; expected '{$this->type}'." );
	}
	}

	/**
	* Call StatsFactory::incrementBy() for the queue overall and for the queue type
	*
	* @param string $event Event type
	* @param string $type Job type
	* @param int $delta
	* @since 1.44
	*/
	protected function incrStats( $event, $type, $delta = 1 ) {
	$this->stats->getCounter( 'jobqueue_events_total' )
	->setLabel( 'event', $event )
	->setLabel( 'type', $type )
	->copyToStatsdAt( [ "jobqueue.{$event}.all", "jobqueue.{$event}.{$type}" ] )
	->incrementBy( $delta );
	}

	/**
	* Subclasses should set this to true if they support type agnostic queues
	*
	* @return bool
	* @since 1.38
	*/
	protected function supportsTypeAgnostic(): bool {
	return false;
	}
	}

	/** @deprecated class alias since 1.44 */
	class_alias( JobQueue::class, 'JobQueue' );

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