DatabaseLockBackend::acquire

public DatabaseLockBackend::acquire($name, $timeout = 30.0)

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) $this->database->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 {
        $this->database->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);
      }
      catch (\Exception $e) {
        // Create the semaphore table if it does not exist and retry.
        if ($this->ensureTableExists()) {
          // Retry only once.
          $retry = !$retry;
        }
        else {
          throw $e;
        }
      }
      // We only retry in case the first attempt failed, but we then broke
      // an expired lock.
    } while ($retry);
  }
  return isset($this->locks[$name]);
}