PhabricatorWorker.php
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	<?php

	/*
	* Copyright 2012 Facebook, Inc.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	/**
	* @task config Configuring Retries and Failures
	*
	* @group worker
	*/
	abstract class PhabricatorWorker {

	private $data;


	/* -( Configuring Retries and Failures )----------------------------------- */


	/**
	* Return the number of seconds this worker needs hold a lease on the task for
	* while it performs work. For most tasks you can leave this at `null`, which
	* will give you a short default lease (currently 60 seconds).
	*
	* For tasks which may take a very long time to complete, you should return
	* an upper bound on the amount of time the task may require.
	*
	* @return int\|null Number of seconds this task needs to remain leased for,
	* or null for a default (currently 60 second) lease.
	*
	* @task config
	*/
	public function getRequiredLeaseTime() {
	return null;
	}


	/**
	* Return the maximum number of times this task may be retried before it
	* is considered permanently failed. By default, tasks retry indefinitely. You
	* can throw a @{class:PhabricatorWorkerPermanentFailureException} to cause an
	* immediate permanent failure.
	*
	* @return int\|null Number of times the task will retry before permanent
	* failure. Return `null` to retry indefinitely.
	*
	* @task config
	*/
	public function getMaximumRetryCount() {
	return null;
	}


	/**
	* Return the number of seconds a task should wait after a failure before
	* retrying. For most tasks you can leave this at `null`, which will give you
	* a short default retry period (currently 60 seconds).
	*
	* @param PhabricatorWorkerTask The task itself. This object is probably
	* useful mostly to examine the failure
	* count if you want to implement staggered
	* retries, or to examine the execution
	* exception if you want to react to
	* different failures in different ways.
	* @param Exception The exception which caused the failure.
	* @return int\|null Number of seconds to wait between retries,
	* or null for a default retry period
	* (currently 60 seconds).
	*
	* @task config
	*/
	public function getWaitBeforeRetry(PhabricatorWorkerTask $task) {
	return null;
	}

	abstract protected function doWork();


	final public function __construct($data) {
	$this->data = $data;
	}

	final protected function getTaskData() {
	return $this->data;
	}

	final public function executeTask() {
	$this->doWork();
	}

	final public static function scheduleTask($task_class, $data) {
	return id(new PhabricatorWorkerActiveTask())
	->setTaskClass($task_class)
	->setData($data)
	->save();
	}


	/**
	* Wait for tasks to complete. If tasks are not leased by other workers, they
	* will be executed in this process while waiting.
	*
	* @param list<int> List of queued task IDs to wait for.
	* @return void
	*/
	final public static function waitForTasks(array $task_ids) {
	$task_table = new PhabricatorWorkerActiveTask();

	$waiting = array_combine($task_ids, $task_ids);
	while ($waiting) {
	$conn_w = $task_table->establishConnection('w');

	// Check if any of the tasks we're waiting on are still queued. If they
	// are not, we're done waiting.
	$row = queryfx_one(
	$conn_w,
	'SELECT COUNT(*) N FROM %T WHERE id IN (%Ld)',
	$task_table->getTableName(),
	$waiting);
	if (!$row['N']) {
	// Nothing is queued anymore. Stop waiting.
	break;
	}

	$tasks = id(new PhabricatorWorkerLeaseQuery())
	->withIDs($waiting)
	->setLimit(1)
	->execute();

	if (!$tasks) {
	// We were not successful in leasing anything. Sleep for a bit and
	// see if we have better luck later.
	sleep(1);
	continue;
	}

	$task = head($tasks)->executeTask();
	}
	}

	}

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