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phab/src/infrastructure/daemon/workers/query/PhabricatorWorkerLeaseQuery.php
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PhabricatorWorkerLeaseQuery.php
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<?php
/**
* 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 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) {
// 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(),
$this->buildWhereClause($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) {
queryfx(
$conn_w,
'UPDATE %T task
SET leaseOwner = %s, leaseExpires = UNIX_TIMESTAMP() + %d
%Q',
$task_table->getTableName(),
$lease_ownership_name,
self::DEFAULT_LEASE_DURATION,
$this->buildUpdateWhereClause($conn_w, $phase, $rows));
$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
WHERE leaseOwner = %s AND leaseExpires > UNIX_TIMESTAMP()
%Q %Q',
$task_table->getTableName(),
$taskdata_table->getTableName(),
$lease_ownership_name,
$this->buildOrderClause($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);
}
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:
$where[] = 'leaseExpires < UNIX_TIMESTAMP()';
break;
default:
throw new Exception("Unknown phase '{$phase}'!");
}
if ($this->ids) {
$where[] = qsprintf(
$conn_w,
'id IN (%Ld)',
$this->ids);
}
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_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 ', $in));
break;
default:
throw new Exception("Unknown phase '{$phase}'!");
}
return $this->formatWhereClause($where);
}
private function buildOrderClause(AphrontDatabaseConnection $conn_w, $phase) {
switch ($phase) {
case self::PHASE_UNLEASED:
// When selecting new tasks, we want to consume them in roughly
// FIFO order, so we order by the task ID.
return qsprintf($conn_w, 'ORDER BY id ASC');
case self::PHASE_EXPIRED:
// When selecting failed tasks, we want to consume them in roughly
// FIFO order of their failures, which is not necessarily their original
// queue order.
// Particularly, this is important for tasks which use soft failures to
// indicate that they are waiting on other tasks to complete: we need to
// push them to the end of the queue after they fail, at least on
// average, so we don't deadlock retrying the same blocked task over
// and over again.
return qsprintf($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;
$parts = array(
getmypid(),
time(),
php_uname('n'),
++$sequence,
);
return implode(':', $parts);
}
}
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