POC: using ResettableTimer to implement KeepAliveManager

KeepAliveManager.java

class KeepAliveManager {
  ResettableTimer shutdownTimer = new ResettableTimer() {
      @Override
      void timerExpired(TimerState state) {
        synchronized (lock) {
          if (!state.isCancelled()) {
            transport.shutdownNow();
          }
        }
      }
    };

  ResettableTimer keepAliveTimer = new ResettableTimer() {
      @Override
      void timerExpired(TimerState state) {
        boolean shouldPing = false;
        synchronized (lock) {
          if (!state.isCancelled()) {
            // false means shutdownTimer is already set, thus we don't need to send another ping.
            shouldPing = shutdownTimer.tryStart();
          }
        }
        if (shouldPing) {
          transport.ping(pingCallback);
        }
      }
    };

  PingCallback pingCallback = new PingCallback() {
      @Override
      public void onSuccess() {
        synchronized (lock) {
          shutdownTimer.stop();
          keepAliveTimer.resetAndStart();
        }
      }
      
      @Override
      public void onFailure() {
        transport.shutdownNow();
      }
    };

  void onDataReceived() {
    synchronized (lock) {
      keepAliveTimer.resetAndStart();
    }
  }

  void onTransportActive() {
    synchronized (lock) {
      keepAliveTimer.resetAndStart();
    }
  }

  void onTransportIdle() {
    synchronized (lock) {
      keepAliveTimer.stop();
      shutdownTimer.stop();
    }
  }
}

line 34: it's a bit more complicated than simply doing "keepAliveTimer.resetAndStart();" after we receive the ping response. onTransportIdle might have been called already so we shouldn't start the timer at this time. I think we probably need more state than "started" and "stopped".