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