function LockBackendAbstract::wait

Overrides LockBackendInterface::wait

File

core/lib/Drupal/Core/Lock/LockBackendAbstract.php, line 29

Class

LockBackendAbstract

Non backend related common methods implementation for lock backends.

Namespace

Code

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;
}