public function DatabaseLockBackend::lockMayBeAvailable

Checks if a lock is available for acquiring.

Parameters

string $name: Lock to acquire.

Return value

bool

Overrides LockBackendInterface::lockMayBeAvailable

File

core/lib/Drupal/Core/Lock/DatabaseLockBackend.php, line 111

Class

DatabaseLockBackend

Defines the database lock backend. This is the default backend in Drupal.

Namespace

Code

public function lockMayBeAvailable($name) {
  $name = $this
    ->normalizeName($name);
  try {
    $lock = $this->database
      ->query('SELECT [expire], [value] FROM {semaphore} WHERE [name] = :name', [
      ':name' => $name,
    ])
      ->fetchAssoc();
  } catch (\Exception $e) {
    $this
      ->catchException($e);

    // If the table does not exist yet then the lock may be available.
    $lock = FALSE;
  }
  if (!$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) $this->database
      ->delete('semaphore')
      ->condition('name', $name)
      ->condition('value', $lock['value'])
      ->condition('expire', 0.0001 + $expire, '<=')
      ->execute();
  }
  return FALSE;
}