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PhabricatorWorkerLeaseQuery.php
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Thu, Jun 27, 06:33

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);
}
}

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