Definition of Drupal\Core\Lock\DatabaseLockBackend.
<?php
/**
* @file
* Definition of Drupal\Core\Lock\DatabaseLockBackend.
*/
namespace Drupal\Core\Lock;
use Drupal\Core\Database\IntegrityConstraintViolationException;
/**
* Defines the database lock backend. This is the default backend in Drupal.
*/
class DatabaseLockBackend extends LockBackendAbstract {
/**
* Implements Drupal\Core\Lock\LockBackedInterface::acquire().
*/
public function acquire($name, $timeout = 30.0) {
// Insure that the timeout is at least 1 ms.
$timeout = max($timeout, 0.001);
$expire = microtime(TRUE) + $timeout;
if (isset($this->locks[$name])) {
// Try to extend the expiration of a lock we already acquired.
$success = (bool) db_update('semaphore')
->fields(array(
'expire' => $expire,
))
->condition('name', $name)
->condition('value', $this
->getLockId())
->execute();
if (!$success) {
// The lock was broken.
unset($this->locks[$name]);
}
return $success;
}
else {
// Optimistically try to acquire the lock, then retry once if it fails.
// The first time through the loop cannot be a retry.
$retry = FALSE;
// We always want to do this code at least once.
do {
try {
db_insert('semaphore')
->fields(array(
'name' => $name,
'value' => $this
->getLockId(),
'expire' => $expire,
))
->execute();
// We track all acquired locks in the global variable.
$this->locks[$name] = TRUE;
// We never need to try again.
$retry = FALSE;
} catch (IntegrityConstraintViolationException $e) {
// Suppress the error. If this is our first pass through the loop,
// then $retry is FALSE. In this case, the insert failed because some
// other request acquired the lock but did not release it. We decide
// whether to retry by checking lockMayBeAvailable(). This will clear
// the offending row from the database table in case it has expired.
$retry = $retry ? FALSE : $this
->lockMayBeAvailable($name);
}
// We only retry in case the first attempt failed, but we then broke
// an expired lock.
} while ($retry);
}
return isset($this->locks[$name]);
}
/**
* Implements Drupal\Core\Lock\LockBackedInterface::lockMayBeAvailable().
*/
public function lockMayBeAvailable($name) {
$lock = db_query('SELECT expire, value FROM {semaphore} WHERE name = :name', array(
':name' => $name,
))
->fetchAssoc();
if (!$lock) {
return TRUE;
}
$expire = (double) $lock['expire'];
$now = microtime(TRUE);
if ($now > $expire) {
// We check two conditions to prevent a race condition where another
// request acquired the lock and set a new expire time. We add a small
// number to $expire to avoid errors with float to string conversion.
return (bool) db_delete('semaphore')
->condition('name', $name)
->condition('value', $lock['value'])
->condition('expire', 0.0001 + $expire, '<=')
->execute();
}
return FALSE;
}
/**
* Implements Drupal\Core\Lock\LockBackedInterface::release().
*/
public function release($name) {
unset($this->locks[$name]);
db_delete('semaphore')
->condition('name', $name)
->condition('value', $this
->getLockId())
->execute();
}
/**
* Implements Drupal\Core\Lock\LockBackedInterface::releaseAll().
*/
public function releaseAll($lock_id = NULL) {
$this->locks = array();
if (empty($lock_id)) {
$lock_id = $this
->getLockId();
}
db_delete('semaphore')
->condition('value', $lock_id)
->execute();
}
}
Name | Description |
---|---|
DatabaseLockBackend | Defines the database lock backend. This is the default backend in Drupal. |