code: public synchronized void start() {
          if (!running) {
              checkState(timer == null);
  
              timer = new java.util.Timer(true); // use daemon thread internally
              schedulePurging(); // schedule timeout to purge cancelled tasks from the timer task queue
  
              running = true;
          }
      }
docs: Start the timer.
  <p/>
  Creates the underlying {@code java.util.Timer} and its task-running daemon thread.
  Following a successful call to {@code start()} subsequent calls are noops.