code: protected function aquireLock()
      {
          $lockfile = $this->lockDir . '/lock';
          // Silence call, since PHP will issue a warning when the file exists.
          // But there is no other way to properly immediately create a lock file
          // only if it does not exist yet.
          $fp = @fopen( $lockfile, 'x' );
  
          if ( $fp === false )
          {
              // Aquiring the lock failed.
              $this->logger->log(
                  sprintf(
                      'The lockfile %s does already exist.',
                      $lockfile
                  ),
                  Logger::WARNING
              );
              return false;
          }
  
          // Store the lock aquiring time in the lock file so this can be
          // debugged more easily and maybe automotically released after
          // stallement.
          fwrite( $fp, time() );
          fclose( $fp );
  
          $this->logger->log( 'Aquired lock.', Logger::INFO );
          return true;
      }
docs: Try to aquire lock
  
  Try to aquire lock - if successful the method will return true - and
  false otherwise.
  
  @return bool