Merge "Typo fix"

[mediawiki.git] / includes / job / JobQueue.php

<?php
/**
 * Job queue base code.
 *
 * 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
 * @defgroup JobQueue JobQueue
 * @author Aaron Schulz
 */

/**
 * Class to handle enqueueing and running of background jobs
 *
 * @ingroup JobQueue
 * @since 1.21
 */
abstract class JobQueue {
        protected $wiki; // string; wiki ID
        protected $type; // string; job type
        protected $order; // string; job priority for pop()
        protected $claimTTL; // integer; seconds
        protected $maxTries; // integer; maximum number of times to try a job
        protected $checkDelay; // boolean; allow delayed jobs

        const QOS_ATOMIC = 1; // integer; "all-or-nothing" job insertions
        const QoS_Atomic = 1; // integer; "all-or-nothing" job insertions (b/c)

        const ROOTJOB_TTL = 2419200; // integer; seconds to remember root jobs (28 days)

        /**
         * @param $params array
         */
        protected function __construct( array $params ) {
                $this->wiki = $params['wiki'];
                $this->type = $params['type'];
                $this->claimTTL = isset( $params['claimTTL'] ) ? $params['claimTTL'] : 0;
                $this->maxTries = isset( $params['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, $this->supportedOrders() ) ) {
                        throw new MWException( __CLASS__ . " does not support '{$this->order}' order." );
                }
                $this->checkDelay = !empty( $params['checkDelay'] );
                if ( $this->checkDelay && !$this->supportsDelayedJobs() ) {
                        throw new MWException( __CLASS__ . " does not support delayed jobs." );
                }
        }

        /**
         * Get a job queue object of the specified type.
         * $params includes:
         *   - class      : What job class to use (determines job type)
         *   - wiki       : wiki 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 choosen, 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 simple means re-inserting them into the queue. Jobs can be
         *                  attempted up to three times before being discarded.
         *   - checkDelay : If supported, respect Job::getReleaseTimestamp() in the push functions.
         *                  This lets delayed jobs wait in a staging area until a given timestamp is
         *                  reached, at which point they will enter the queue. If this is not enabled
         *                  or not supported, an exception will be thrown on delayed job insertion.
         *
         * Queue classes should throw an exception if they do not support the options given.
         *
         * @param $params array
         * @return JobQueue
         * @throws MWException
         */
        final public static function factory( array $params ) {
                $class = $params['class'];
                if ( !class_exists( $class ) ) {
                        throw new MWException( "Invalid job queue class '$class'." );
                }
                $obj = new $class( $params );
                if ( !( $obj instanceof self ) ) {
                        throw new MWException( "Class '$class' is not a " . __CLASS__ . " class." );
                }
                return $obj;
        }

        /**
         * @return string Wiki ID
         */
        final public function getWiki() {
                return $this->wiki;
        }

        /**
         * @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;
        }

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

        /**
         * 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
         *
         * @return boolean Whether delayed jobs are supported
         */
        protected function supportsDelayedJobs() {
                return false; // not implemented
        }

        /**
         * 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 affect is typically
         * not distinguishable from the race condition between isEmpty() and pop().
         *
         * @return bool
         * @throws MWException
         */
        final public function isEmpty() {
                wfProfileIn( __METHOD__ );
                $res = $this->doIsEmpty();
                wfProfileOut( __METHOD__ );
                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 integer
         * @throws MWException
         */
        final public function getSize() {
                wfProfileIn( __METHOD__ );
                $res = $this->doGetSize();
                wfProfileOut( __METHOD__ );
                return $res;
        }

        /**
         * @see JobQueue::getSize()
         * @return integer
         */
        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 integer
         * @throws MWException
         */
        final public function getAcquiredCount() {
                wfProfileIn( __METHOD__ );
                $res = $this->doGetAcquiredCount();
                wfProfileOut( __METHOD__ );
                return $res;
        }

        /**
         * @see JobQueue::getAcquiredCount()
         * @return integer
         */
        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 integer
         * @throws MWException
         * @since 1.22
         */
        final public function getDelayedCount() {
                wfProfileIn( __METHOD__ );
                $res = $this->doGetDelayedCount();
                wfProfileOut( __METHOD__ );
                return $res;
        }

        /**
         * @see JobQueue::getDelayedCount()
         * @return integer
         */
        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 integer
         * @throws MWException
         */
        final public function getAbandonedCount() {
                wfProfileIn( __METHOD__ );
                $res = $this->doGetAbandonedCount();
                wfProfileOut( __METHOD__ );
                return $res;
        }

        /**
         * @see JobQueue::getAbandonedCount()
         * @return integer
         */
        protected function doGetAbandonedCount() {
                return 0; // not implemented
        }

        /**
         * Push a single 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 $jobs Job|Array
         * @param $flags integer Bitfield (supports JobQueue::QOS_ATOMIC)
         * @return bool Returns false on failure
         * @throws MWException
         */
        final public function push( $jobs, $flags = 0 ) {
                return $this->batchPush( is_array( $jobs ) ? $jobs : array( $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 array $jobs List of Jobs
         * @param $flags integer Bitfield (supports JobQueue::QOS_ATOMIC)
         * @return bool Returns false on failure
         * @throws MWException
         */
        final public function batchPush( array $jobs, $flags = 0 ) {
                if ( !count( $jobs ) ) {
                        return true; // nothing to do
                }

                foreach ( $jobs as $job ) {
                        if ( $job->getType() !== $this->type ) {
                                throw new MWException(
                                        "Got '{$job->getType()}' job; expected a '{$this->type}' job." );
                        } elseif ( $job->getReleaseTimestamp() && !$this->checkDelay ) {
                                throw new MWException(
                                        "Got delayed '{$job->getType()}' job; delays are not supported." );
                        }
                }

                wfProfileIn( __METHOD__ );
                $ok = $this->doBatchPush( $jobs, $flags );
                wfProfileOut( __METHOD__ );
                return $ok;
        }

        /**
         * @see JobQueue::batchPush()
         * @return bool
         */
        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.
         *
         * @return Job|bool Returns false if there are no jobs
         * @throws MWException
         */
        final public function pop() {
                global $wgJobClasses;

                if ( $this->wiki !== wfWikiID() ) {
                        throw new MWException( "Cannot pop '{$this->type}' job off foreign wiki queue." );
                } elseif ( !isset( $wgJobClasses[$this->type] ) ) {
                        // Do not pop jobs if there is no class for the queue type
                        throw new MWException( "Unrecognized job type '{$this->type}'." );
                }

                wfProfileIn( __METHOD__ );
                $job = $this->doPop();
                wfProfileOut( __METHOD__ );

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

                return $job;
        }

        /**
         * @see JobQueue::pop()
         * @return Job
         */
        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 $job Job
         * @return bool
         * @throws MWException
         */
        final public function ack( Job $job ) {
                if ( $job->getType() !== $this->type ) {
                        throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
                }
                wfProfileIn( __METHOD__ );
                $ok = $this->doAck( $job );
                wfProfileOut( __METHOD__ );
                return $ok;
        }

        /**
         * @see JobQueue::ack()
         * @return bool
         */
        abstract protected function doAck( Job $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 potentially many refreshLinks2 jobs.
         * Since these jobs include things like page ID ranges and DB master positions, and morph
         * into smaller refreshLinks2 jobs recursively, simple duplicate detection (like job_sha1)
         * for individual jobs being identical 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.
         *
         * @param $job Job
         * @return bool
         * @throws MWException
         */
        final public function deduplicateRootJob( Job $job ) {
                if ( $job->getType() !== $this->type ) {
                        throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
                }
                wfProfileIn( __METHOD__ );
                $ok = $this->doDeduplicateRootJob( $job );
                wfProfileOut( __METHOD__ );
                return $ok;
        }

        /**
         * @see JobQueue::deduplicateRootJob()
         * @param $job Job
         * @return bool
         */
        protected function doDeduplicateRootJob( Job $job ) {
                global $wgMemc;

                if ( !$job->hasRootJobParams() ) {
                        throw new MWException( "Cannot register root job; missing parameters." );
                }
                $params = $job->getRootJobParams();

                $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
                // Callers should call batchInsert() and then this function so that if the insert
                // fails, the de-duplication registration will be aborted. Since the insert is
                // deferred till "transaction idle", do the same here, so that the ordering is
                // maintained. Having only the de-duplication registration succeed would cause
                // jobs to become no-ops without any actual jobs that made them redundant.
                $timestamp = $wgMemc->get( $key ); // current last timestamp of this job
                if ( $timestamp && $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 $wgMemc->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
        }

        /**
         * Check if the "root" job of a given job has been superseded by a newer one
         *
         * @param $job Job
         * @return bool
         * @throws MWException
         */
        final protected function isRootJobOldDuplicate( Job $job ) {
                if ( $job->getType() !== $this->type ) {
                        throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
                }
                wfProfileIn( __METHOD__ );
                $isDuplicate = $this->doIsRootJobOldDuplicate( $job );
                wfProfileOut( __METHOD__ );
                return $isDuplicate;
        }

        /**
         * @see JobQueue::isRootJobOldDuplicate()
         * @param Job $job
         * @return bool
         */
        protected function doIsRootJobOldDuplicate( Job $job ) {
                global $wgMemc;

                if ( !$job->hasRootJobParams() ) {
                        return false; // job has no de-deplication info
                }
                $params = $job->getRootJobParams();

                // Get the last time this root job was enqueued
                $timestamp = $wgMemc->get( $this->getRootJobCacheKey( $params['rootJobSignature'] ) );

                // 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
         * @return string
         */
        protected function getRootJobCacheKey( $signature ) {
                list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
                return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
        }

        /**
         * Deleted all unclaimed and delayed jobs from the queue
         *
         * @return bool Success
         * @throws MWException
         * @since 1.22
         */
        final public function delete() {
                wfProfileIn( __METHOD__ );
                $res = $this->doDelete();
                wfProfileOut( __METHOD__ );
                return $res;
        }

        /**
         * @see JobQueue::delete()
         * @return bool Success
         */
        protected function doDelete() {
                throw new MWException( "This method is not implemented." );
        }

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

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

        /**
         * Return a map of task names to task definition maps.
         * A "task" is a fast periodic queue maintenance action.
         * Mutually exclusive tasks must implement their own locking in the callback.
         *
         * Each task value is an associative array with:
         *   - name     : the name of the task
         *   - callback : a PHP callable that performs the task
         *   - period   : the period in seconds corresponding to the task frequency
         *
         * @return Array
         */
        final public function getPeriodicTasks() {
                $tasks = $this->doGetPeriodicTasks();
                foreach ( $tasks as $name => &$def ) {
                        $def['name'] = $name;
                }
                return $tasks;
        }

        /**
         * @see JobQueue::getPeriodicTasks()
         * @return Array
         */
        protected function doGetPeriodicTasks() {
                return array();
        }

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

        /**
         * @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
         * @throws MWException
         */
        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.
         *
         * @return Iterator
         * @throws MWException
         * @since 1.22
         */
        public function getAllDelayedJobs() {
                return new ArrayIterator( array() ); // not implemented
        }

        /**
         * Call wfIncrStats() for the queue overall and for the queue type
         *
         * @param string $key Event type
         * @param string $type Job type
         * @param integer $delta
         * @since 1.22
         */
        public static function incrStats( $key, $type, $delta = 1 ) {
                wfIncrStats( $key, $delta );
                wfIncrStats( "{$key}-{$type}", $delta );
        }

        /**
         * Namespace the queue with a key to isolate it for testing
         *
         * @param $key string
         * @return void
         * @throws MWException
         */
        public function setTestingPrefix( $key ) {
                throw new MWException( "Queue namespacing not supported for this queue type." );
        }
}