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<?php
namespace Drupal\Core\Lock;
/**
* Non backend related common methods implementation for lock backends.
*
* @ingroup lock
*/
abstract class LockBackendAbstract implements LockBackendInterface {
/**
* Current page lock token identifier.
*
* @var string
*/
protected $lockId;
/**
* Existing locks for this page.
*
* @var array
*/
protected $locks = [];
/**
* {@inheritdoc}
*/
public function wait($name, $delay = 30) {
// Pause the process for short periods between calling
// lock_may_be_available(). This prevents hitting the database with constant
// database queries while waiting, which could lead to performance issues.
// However, if the wait period is too long, there is the potential for a
// large number of processes to be blocked waiting for a lock, especially
// if the item being rebuilt is commonly requested. To address both of these
// concerns, begin waiting for 25ms, then add 25ms to the wait period each
// time until it reaches 500ms. After this point polling will continue every
// 500ms until $delay is reached.
// $delay is passed in seconds, but we will be using usleep(), which takes
// microseconds as a parameter. Multiply it by 1 million so that all
// further numbers are equivalent.
$delay = (int) $delay * 1000000;
// Begin sleeping at 25ms.
$sleep = 25000;
while ($delay > 0) {
// This function should only be called by a request that failed to get a
// lock, so we sleep first to give the parallel request a chance to finish
// and release the lock.
usleep($sleep);
// After each sleep, increase the value of $sleep until it reaches
// 500ms, to reduce the potential for a lock stampede.
$delay = $delay - $sleep;
$sleep = min(500000, $sleep + 25000, $delay);
if ($this->lockMayBeAvailable($name)) {
// No longer need to wait.
return FALSE;
}
}
// The caller must still wait longer to get the lock.
return TRUE;
}
/**
* {@inheritdoc}
*/
public function getLockId() {
if (!isset($this->lockId)) {
$this->lockId = uniqid((string) mt_rand(), TRUE);
}
return $this->lockId;
}
}
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