PhabricatorWorkerLeaseQuery.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.
	*/

	/**
	* Select and lease tasks from the worker task queue.
	*
	* @group worker
	*/
	final class PhabricatorWorkerLeaseQuery extends PhabricatorQuery {

	const PHASE_UNLEASED = 'unleased';
	const PHASE_EXPIRED = 'expired';
	const PHASE_SELECT = 'select';

	const DEFAULT_LEASE_DURATION = 60; // Seconds

	private $ids;
	private $limit;

	public function withIDs(array $ids) {
	$this->ids = $ids;
	return $this;
	}

	public function setLimit($limit) {
	$this->limit = $limit;
	return $this;
	}

	public function execute() {
	if (!$this->limit) {
	throw new Exception("You must setLimit() when leasing tasks.");
	}

	$task_table = new PhabricatorWorkerActiveTask();
	$taskdata_table = new PhabricatorWorkerTaskData();
	$lease_ownership_name = $this->getLeaseOwnershipName();

	$conn_w = $task_table->establishConnection('w');

	// Try to satisfy the request from new, unleased tasks first. If we don't
	// find enough tasks, try tasks with expired leases (i.e., tasks which have
	// previously failed).

	$phases = array(
	self::PHASE_UNLEASED,
	self::PHASE_EXPIRED,
	);
	$limit = $this->limit;

	$leased = 0;
	foreach ($phases as $phase) {
	queryfx(
	$conn_w,
	'UPDATE %T task
	SET leaseOwner = %s, leaseExpires = UNIX_TIMESTAMP() + %d
	%Q %Q %Q',
	$task_table->getTableName(),
	$lease_ownership_name,
	self::DEFAULT_LEASE_DURATION,
	$this->buildWhereClause($conn_w, $phase),
	$this->buildOrderClause($conn_w),
	$this->buildLimitClause($conn_w, $limit - $leased));

	$leased += $conn_w->getAffectedRows();
	if ($leased == $limit) {
	break;
	}
	}

	if (!$leased) {
	return array();
	}

	$data = queryfx_all(
	$conn_w,
	'SELECT task.*, taskdata.data _taskData, UNIX_TIMESTAMP() _serverTime
	FROM %T task LEFT JOIN %T taskdata
	ON taskdata.id = task.dataID
	%Q %Q %Q',
	$task_table->getTableName(),
	$taskdata_table->getTableName(),
	$this->buildWhereClause($conn_w, self::PHASE_SELECT),
	$this->buildOrderClause($conn_w),
	$this->buildLimitClause($conn_w, $limit));

	$tasks = $task_table->loadAllFromArray($data);
	$tasks = mpull($tasks, null, 'getID');

	foreach ($data as $row) {
	$tasks[$row['id']]->setServerTime($row['_serverTime']);
	if ($row['_taskData']) {
	$task_data = json_decode($row['_taskData'], true);
	} else {
	$task_data = null;
	}
	$tasks[$row['id']]->setData($task_data);
	}

	return $tasks;
	}

	private function buildWhereClause(AphrontDatabaseConnection $conn_w, $phase) {
	$where = array();

	switch ($phase) {
	case self::PHASE_UNLEASED:
	$where[] = 'leaseOwner IS NULL';
	break;
	case self::PHASE_EXPIRED:
	$where[] = 'leaseExpires < UNIX_TIMESTAMP()';
	break;
	case self::PHASE_SELECT:
	$where[] = qsprintf(
	$conn_w,
	'leaseOwner = %s',
	$this->getLeaseOwnershipName());
	$where[] = 'leaseExpires > UNIX_TIMESTAMP()';
	break;
	default:
	throw new Exception("Unknown phase '{$phase}'!");
	}

	if ($this->ids) {
	$where[] = qsprintf(
	$conn_w,
	'task.id IN (%Ld)',
	$this->ids);
	}

	return $this->formatWhereClause($where);
	}

	private function buildOrderClause(AphrontDatabaseConnection $conn_w) {
	return qsprintf($conn_w, 'ORDER BY id ASC');
	}

	private function buildLimitClause(AphrontDatabaseConnection $conn_w, $limit) {
	return qsprintf($conn_w, 'LIMIT %d', $limit);
	}

	private function getLeaseOwnershipName() {
	static $name = null;
	if ($name === null) {
	$name = getmypid().':'.time().':'.php_uname('n');
	}
	return $name;
	}

	}

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