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PhabricatorWorkerLeaseQuery.php
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			<?php

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

			const PHASE_LEASED = 'leased';
			const PHASE_UNLEASED = 'unleased';
			const PHASE_EXPIRED = 'expired';

			private $ids;
			private $objectPHIDs;
			private $limit;
			private $skipLease;
			private $leased = false;

			public static function getDefaultWaitBeforeRetry() {
			return phutil_units('5 minutes in seconds');
			}

			public static function getDefaultLeaseDuration() {
			return phutil_units('2 hours in seconds');
			}

			/**
			* Set this flag to select tasks from the top of the queue without leasing
			* them.
			*
			* This can be used to show which tasks are coming up next without altering
			* the queue's behavior.
			*
			* @param bool True to skip the lease acquisition step.
			*/
			public function setSkipLease($skip) {
			$this->skipLease = $skip;
			return $this;
			}

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

			public function withObjectPHIDs(array $phids) {
			$this->objectPHIDs = $phids;
			return $this;
			}

			/**
			* Select only leased tasks, only unleased tasks, or both types of task.
			*
			* By default, queries select only unleased tasks (equivalent to passing
			* `false` to this method). You can pass `true` to select only leased tasks,
			* or `null` to ignore the lease status of tasks.
			*
			* If your result set potentially includes leased tasks, you must disable
			* leasing using @{method:setSkipLease}. These options are intended for use
			* when displaying task status information.
			*
			* @param mixed `true` to select only leased tasks, `false` to select only
			* unleased tasks (default), or `null` to select both.
			* @return this
			*/
			public function withLeasedTasks($leased) {
			$this->leased = $leased;
			return $this;
			}

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

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

			if ($this->leased !== false) {
			if (!$this->skipLease) {
			throw new Exception(
			pht(
			'If you potentially select leased tasks using %s, '.
			'you MUST disable lease acquisition by calling %s.',
			'withLeasedTasks()',
			'setSkipLease()'));
			}
			}

			$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).

			// If we're selecting leased tasks, look for them first.

			$phases = array();
			if ($this->leased !== false) {
			$phases[] = self::PHASE_LEASED;
			}
			if ($this->leased !== true) {
			$phases[] = self::PHASE_UNLEASED;
			$phases[] = self::PHASE_EXPIRED;
			}
			$limit = $this->limit;

			$leased = 0;
			$task_ids = array();
			foreach ($phases as $phase) {
			// NOTE: If we issue `UPDATE ... WHERE ... ORDER BY id ASC`, the query
			// goes very, very slowly. The `ORDER BY` triggers this, although we get
			// the same apparent results without it. Without the ORDER BY, binary
			// read slaves complain that the query isn't repeatable. To avoid both
			// problems, do a SELECT and then an UPDATE.

			$rows = queryfx_all(
			$conn_w,
			'SELECT id, leaseOwner FROM %T %Q %Q %Q',
			$task_table->getTableName(),
			$this->buildCustomWhereClause($conn_w, $phase),
			$this->buildOrderClause($conn_w, $phase),
			$this->buildLimitClause($conn_w, $limit - $leased));

			// NOTE: Sometimes, we'll race with another worker and they'll grab
			// this task before we do. We could reduce how often this happens by
			// selecting more tasks than we need, then shuffling them and trying
			// to lock only the number we're actually after. However, the amount
			// of time workers spend here should be very small relative to their
			// total runtime, so keep it simple for the moment.

			if ($rows) {
			if ($this->skipLease) {
			$leased += count($rows);
			$task_ids += array_fuse(ipull($rows, 'id'));
			} else {
			queryfx(
			$conn_w,
			'UPDATE %T task
			SET leaseOwner = %s, leaseExpires = UNIX_TIMESTAMP() + %d
			%Q',
			$task_table->getTableName(),
			$lease_ownership_name,
			self::getDefaultLeaseDuration(),
			$this->buildUpdateWhereClause($conn_w, $phase, $rows));

			$leased += $conn_w->getAffectedRows();
			}

			if ($leased == $limit) {
			break;
			}
			}
			}

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

			if ($this->skipLease) {
			$selection_condition = qsprintf(
			$conn_w,
			'task.id IN (%Ld)',
			$task_ids);
			} else {
			$selection_condition = qsprintf(
			$conn_w,
			'task.leaseOwner = %s AND leaseExpires > UNIX_TIMESTAMP()',
			$lease_ownership_name);
			}

			$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
			WHERE %Q %Q %Q',
			$task_table->getTableName(),
			$taskdata_table->getTableName(),
			$selection_condition,
			$this->buildOrderClause($conn_w, $phase),
			$this->buildLimitClause($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);
			}

			if ($this->skipLease) {
			// Reorder rows into the original phase order if this is a status query.
			$tasks = array_select_keys($tasks, $task_ids);
			}

			return $tasks;
			}

			protected function buildCustomWhereClause(
			AphrontDatabaseConnection $conn_w,
			$phase) {

			$where = array();

			switch ($phase) {
			case self::PHASE_LEASED:
			$where[] = 'leaseOwner IS NOT NULL';
			$where[] = 'leaseExpires >= UNIX_TIMESTAMP()';
			break;
			case self::PHASE_UNLEASED:
			$where[] = 'leaseOwner IS NULL';
			break;
			case self::PHASE_EXPIRED:
			$where[] = 'leaseExpires < UNIX_TIMESTAMP()';
			break;
			default:
			throw new Exception(pht("Unknown phase '%s'!", $phase));
			}

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

			if ($this->objectPHIDs !== null) {
			$where[] = qsprintf($conn_w, 'objectPHID IN (%Ls)', $this->objectPHIDs);
			}

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

			private function buildUpdateWhereClause(
			AphrontDatabaseConnection $conn_w,
			$phase,
			array $rows) {

			$where = array();

			// NOTE: This is basically working around the MySQL behavior that
			// `IN (NULL)` doesn't match NULL.

			switch ($phase) {
			case self::PHASE_LEASED:
			throw new Exception(
			pht(
			'Trying to lease tasks selected in the leased phase! This is '.
			'intended to be impossible.'));
			case self::PHASE_UNLEASED:
			$where[] = qsprintf($conn_w, 'leaseOwner IS NULL');
			$where[] = qsprintf($conn_w, 'id IN (%Ld)', ipull($rows, 'id'));
			break;
			case self::PHASE_EXPIRED:
			$in = array();
			foreach ($rows as $row) {
			$in[] = qsprintf(
			$conn_w,
			'(id = %d AND leaseOwner = %s)',
			$row['id'],
			$row['leaseOwner']);
			}
			$where[] = qsprintf($conn_w, '(%Q)', implode(' OR ', $in));
			break;
			default:
			throw new Exception(pht('Unknown phase "%s"!', $phase));
			}

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

			private function buildOrderClause(AphrontDatabaseConnection $conn_w, $phase) {
			switch ($phase) {
			case self::PHASE_LEASED:
			// Ideally we'd probably order these by lease acquisition time, but
			// we don't have that handy and this is a good approximation.
			return qsprintf($conn_w, 'ORDER BY priority ASC, id ASC');
			case self::PHASE_UNLEASED:
			// When selecting new tasks, we want to consume them in order of
			// increasing priority (and then FIFO).
			return qsprintf($conn_w, 'ORDER BY priority ASC, id ASC');
			case self::PHASE_EXPIRED:
			// When selecting failed tasks, we want to consume them in roughly
			// FIFO order of their failures, which is not necessarily their original
			// queue order.

			// Particularly, this is important for tasks which use soft failures to
			// indicate that they are waiting on other tasks to complete: we need to
			// push them to the end of the queue after they fail, at least on
			// average, so we don't deadlock retrying the same blocked task over
			// and over again.
			return qsprintf($conn_w, 'ORDER BY leaseExpires ASC');
			default:
			throw new Exception(pht('Unknown phase "%s"!', $phase));
			}
			}

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

			private function getLeaseOwnershipName() {
			static $sequence = 0;

			// TODO: If the host name is very long, this can overflow the 64-character
			// column, so we pick just the first part of the host name. It might be
			// useful to just use a random hash as the identifier instead and put the
			// pid / time / host (which are somewhat useful diagnostically) elsewhere.
			// Likely, we could store a daemon ID instead and use that to identify
			// when and where code executed. See T6742.

			$host = php_uname('n');
			$host = id(new PhutilUTF8StringTruncator())
			->setMaximumBytes(32)
			->setTerminator('...')
			->truncateString($host);

			$parts = array(
			getmypid(),
			time(),
			$host,
			++$sequence,
			);

			return implode(':', $parts);
			}

			}

phab/src/infrastructure/daemon/workers/query/PhabricatorWorkerLeaseQuery.php3215899925e2feature/testing

PhabricatorWorkerLeaseQuery.phpView Options

phab/src/infrastructure/daemon/workers/query/PhabricatorWorkerLeaseQuery.php
3215899925e2feature/testing

PhabricatorWorkerLeaseQuery.php
View Options