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13 * GNU General Public License for more details.
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21 * @defgroup JobQueue JobQueue
22 * @author Aaron Schulz
26 * Class to handle enqueueing and running of background jobs
31 abstract class JobQueue
{
32 protected $wiki; // string; wiki ID
33 protected $type; // string; job type
34 protected $order; // string; job priority for pop()
35 protected $claimTTL; // integer; seconds
37 const QoS_Atomic
= 1; // integer; "all-or-nothing" job insertions
39 const MAX_ATTEMPTS
= 3; // integer; number of times to try a job
42 * @param $params array
44 protected function __construct( array $params ) {
45 $this->wiki
= $params['wiki'];
46 $this->type
= $params['type'];
47 $this->order
= isset( $params['order'] ) ?
$params['order'] : 'random';
48 $this->claimTTL
= isset( $params['claimTTL'] ) ?
$params['claimTTL'] : 0;
52 * Get a job queue object of the specified type.
54 * - class : What job class to use (determines job type)
55 * - wiki : wiki ID of the wiki the jobs are for (defaults to current wiki)
56 * - type : The name of the job types this queue handles
57 * - order : Order that pop() selects jobs, one of "fifo", "timestamp" or "random".
58 * If "fifo" is used, the queue will effectively be FIFO. Note that
59 * job completion will not appear to be exactly FIFO if there are multiple
60 * job runners since jobs can take different times to finish once popped.
61 * If "timestamp" is used, the queue will at least be loosely ordered
62 * by timestamp, allowing for some jobs to be popped off out of order.
63 * If "random" is used, pop() will pick jobs in random order. This might be
64 * useful for improving concurrency depending on the queue storage medium.
65 * - claimTTL : If supported, the queue will recycle jobs that have been popped
66 * but not acknowledged as completed after this many seconds. Recycling
67 * of jobs simple means re-inserting them into the queue. Jobs can be
68 * attempted up to three times before being discarded.
70 * Queue classes should throw an exception if they do not support the options given.
72 * @param $params array
76 final public static function factory( array $params ) {
77 $class = $params['class'];
78 if ( !MWInit
::classExists( $class ) ) {
79 throw new MWException( "Invalid job queue class '$class'." );
81 $obj = new $class( $params );
82 if ( !( $obj instanceof self
) ) {
83 throw new MWException( "Class '$class' is not a " . __CLASS__
. " class." );
89 * @return string Wiki ID
91 final public function getWiki() {
96 * @return string Job type that this queue handles
98 final public function getType() {
103 * Quickly check if the queue is empty (has no available jobs).
104 * Queue classes should use caching if they are any slower without memcached.
108 final public function isEmpty() {
109 wfProfileIn( __METHOD__
);
110 $res = $this->doIsEmpty();
111 wfProfileOut( __METHOD__
);
116 * @see JobQueue::isEmpty()
119 abstract protected function doIsEmpty();
122 * Get the number of available jobs in the queue.
123 * Queue classes should use caching if they are any slower without memcached.
127 final public function getSize() {
128 wfProfileIn( __METHOD__
);
129 $res = $this->doGetSize();
130 wfProfileOut( __METHOD__
);
135 * @see JobQueue::getSize()
138 abstract protected function doGetSize();
141 * Get the number of acquired jobs (these are temporarily out of the queue).
142 * Queue classes should use caching if they are any slower without memcached.
146 final public function getAcquiredCount() {
147 wfProfileIn( __METHOD__
);
148 $res = $this->doGetAcquiredCount();
149 wfProfileOut( __METHOD__
);
154 * @see JobQueue::getAcquiredCount()
157 abstract protected function doGetAcquiredCount();
160 * Push a single jobs into the queue.
161 * This does not require $wgJobClasses to be set for the given job type.
163 * @param $jobs Job|Array
164 * @param $flags integer Bitfield (supports JobQueue::QoS_Atomic)
165 * @throws MWException
166 * @return bool Returns false on failure
168 final public function push( $jobs, $flags = 0 ) {
169 $jobs = is_array( $jobs ) ?
$jobs : array( $jobs );
171 return $this->batchPush( $jobs, $flags );
175 * Push a batch of jobs into the queue.
176 * This does not require $wgJobClasses to be set for the given job type.
178 * @param $jobs array List of Jobs
179 * @param $flags integer Bitfield (supports JobQueue::QoS_Atomic)
180 * @throws MWException
181 * @return bool Returns false on failure
183 final public function batchPush( array $jobs, $flags = 0 ) {
184 foreach ( $jobs as $job ) {
185 if ( $job->getType() !== $this->type
) {
186 throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
189 wfProfileIn( __METHOD__
);
190 $ok = $this->doBatchPush( $jobs, $flags );
191 wfProfileOut( __METHOD__
);
196 * @see JobQueue::batchPush()
199 abstract protected function doBatchPush( array $jobs, $flags );
202 * Pop a job off of the queue.
203 * This requires $wgJobClasses to be set for the given job type.
205 * @return Job|bool Returns false on failure
207 final public function pop() {
208 wfProfileIn( __METHOD__
);
209 $job = $this->doPop();
210 wfProfileOut( __METHOD__
);
215 * @see JobQueue::pop()
218 abstract protected function doPop();
221 * Acknowledge that a job was completed.
223 * This does nothing for certain queue classes or if "claimTTL" is not set.
226 * @throws MWException
229 final public function ack( Job
$job ) {
230 if ( $job->getType() !== $this->type
) {
231 throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
233 wfProfileIn( __METHOD__
);
234 $ok = $this->doAck( $job );
235 wfProfileOut( __METHOD__
);
240 * @see JobQueue::ack()
243 abstract protected function doAck( Job
$job );
246 * Register the "root job" of a given job into the queue for de-duplication.
247 * This should only be called right *after* all the new jobs have been inserted.
248 * This is used to turn older, duplicate, job entries into no-ops. The root job
249 * information will remain in the registry until it simply falls out of cache.
251 * This requires that $job has two special fields in the "params" array:
252 * - rootJobSignature : hash (e.g. SHA1) that identifies the task
253 * - rootJobTimestamp : TS_MW timestamp of this instance of the task
255 * A "root job" is a conceptual job that consist of potentially many smaller jobs
256 * that are actually inserted into the queue. For example, "refreshLinks" jobs are
257 * spawned when a template is edited. One can think of the task as "update links
258 * of pages that use template X" and an instance of that task as a "root job".
259 * However, what actually goes into the queue are potentially many refreshLinks2 jobs.
260 * Since these jobs include things like page ID ranges and DB master positions, and morph
261 * into smaller refreshLinks2 jobs recursively, simple duplicate detection (like job_sha1)
262 * for individual jobs being identical is not useful.
264 * In the case of "refreshLinks", if these jobs are still in the queue when the template
265 * is edited again, we want all of these old refreshLinks jobs for that template to become
266 * no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
267 * Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
268 * previous "root job" for the same task of "update links of pages that use template X".
270 * This does nothing for certain queue classes.
273 * @throws MWException
276 final public function deduplicateRootJob( Job
$job ) {
277 if ( $job->getType() !== $this->type
) {
278 throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
280 wfProfileIn( __METHOD__
);
281 $ok = $this->doDeduplicateRootJob( $job );
282 wfProfileOut( __METHOD__
);
287 * @see JobQueue::deduplicateRootJob()
291 protected function doDeduplicateRootJob( Job
$job ) {
296 * Wait for any slaves or backup servers to catch up.
298 * This does nothing for certain queue classes.
302 final public function waitForBackups() {
303 wfProfileIn( __METHOD__
);
304 $this->doWaitForBackups();
305 wfProfileOut( __METHOD__
);
309 * @see JobQueue::waitForBackups()
312 protected function doWaitForBackups() {}