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<?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
const QoS_Atomic = 1; // integer; "all-or-nothing" job insertions
/**
* @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." );
}
}
/**
* 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.
*
* 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 ( !MWInit::classExists( $class ) ) {
throw new MWException( "Invalid job queue class '$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)
*/
final public function getOrder() {
return $this->order;
}
/**
* @return Array Subset of (random, timestamp, fifo)
*/
abstract protected function supportedOrders();
/**
* @return string One of (random, timestamp, fifo)
*/
abstract protected function optimalOrder();
/**
* Quickly check if the queue is empty (has no available 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) 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();
/**
* 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 '{$this->type}'." );
}
}
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__ );
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 ) {
return true;
}
/**
* 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 of the jobs in this queue.
* This does not include jobs that are current acquired. In general,
* this should only be called on a queue that is no longer being popped.
*
* @return Iterator|Traversable|Array
* @throws MWException
*/
abstract public function getAllQueuedJobs();
/**
* 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." );
}
}