public static void loop() {
    final Looper me = myLooper();
    if (me == null) {
      throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
    }
    final MessageQueue queue = me.mQueue;

    // Make sure the identity of this thread is that of the local process,
    // and keep track of what that identity token actually is.
    Binder.clearCallingIdentity();
    final long ident = Binder.clearCallingIdentity();

    // Allow overriding a threshold with a system prop. e.g.
    // adb shell 'setprop log.looper.1000.main.slow 1 && stop && start'
    final int thresholdOverride =
        SystemProperties.getInt("log.looper."
            + Process.myUid() + "."
            + Thread.currentThread().getName()
            + ".slow", 0);

    boolean slowDeliveryDetected = false;

    for (;;) {
      Message msg = queue.next(); // might block
      if (msg == null) {
        // No message indicates that the message queue is quitting.
        return;
      }

      // This must be in a local variable, in case a UI event sets the logger
      final Printer logging = me.mLogging;
      if (logging != null) {
        logging.println(">>>>> Dispatching to " + msg.target + " " +
            msg.callback + ": " + msg.what);
      }
      // Make sure the observer won't change while processing a transaction.
      final Observer observer = sObserver;

      final long traceTag = me.mTraceTag;
      long slowDispatchThresholdMs = me.mSlowDispatchThresholdMs;
      long slowDeliveryThresholdMs = me.mSlowDeliveryThresholdMs;
      if (thresholdOverride > 0) {
        slowDispatchThresholdMs = thresholdOverride;
        slowDeliveryThresholdMs = thresholdOverride;
      }
      final boolean logSlowDelivery = (slowDeliveryThresholdMs > 0) && (msg.when > 0);
      final boolean logSlowDispatch = (slowDispatchThresholdMs > 0);

      final boolean needStartTime = logSlowDelivery || logSlowDispatch;
      final boolean needEndTime = logSlowDispatch;

      if (traceTag != 0 && Trace.isTagEnabled(traceTag)) {
        Trace.traceBegin(traceTag, msg.target.getTraceName(msg));
      }

      final long dispatchStart = needStartTime ? SystemClock.uptimeMillis() : 0;
      final long dispatchEnd;
      Object token = null;
      if (observer != null) {
        token = observer.messageDispatchStarting();
      }
      long origWorkSource = ThreadLocalWorkSource.setUid(msg.workSourceUid);
      try {
        msg.target.dispatchMessage(msg);
        if (observer != null) {
          observer.messageDispatched(token, msg);
        }
        dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0;
      } catch (Exception exception) {
        if (observer != null) {
          observer.dispatchingThrewException(token, msg, exception);
        }
        throw exception;
      } finally {
        ThreadLocalWorkSource.restore(origWorkSource);
        if (traceTag != 0) {
          Trace.traceEnd(traceTag);
        }
      }
      if (logSlowDelivery) {
        if (slowDeliveryDetected) {
          if ((dispatchStart - msg.when) <= 10) {
            Slog.w(TAG, "Drained");
            slowDeliveryDetected = false;
          }
        } else {
          if (showSlowLog(slowDeliveryThresholdMs, msg.when, dispatchStart, "delivery",
              msg)) {
            // Once we write a slow delivery log, suppress until the queue drains.
            slowDeliveryDetected = true;
          }
        }
      }
      if (logSlowDispatch) {
        showSlowLog(slowDispatchThresholdMs, dispatchStart, dispatchEnd, "dispatch", msg);
      }

      if (logging != null) {
        logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
      }

      // Make sure that during the course of dispatching the
      // identity of the thread wasn't corrupted.
      final long newIdent = Binder.clearCallingIdentity();
      if (ident != newIdent) {
        Log.wtf(TAG, "Thread identity changed from 0x"
            + Long.toHexString(ident) + " to 0x"
            + Long.toHexString(newIdent) + " while dispatching to "
            + msg.target.getClass().getName() + " "
            + msg.callback + " what=" + msg.what);
      }

      msg.recycleUnchecked();
    }
  }

/**
   * Control logging of messages as they are processed by this Looper. If
   * enabled, a log message will be written to <var>printer</var>
   * at the beginning and ending of each message dispatch, identifying the
   * target Handler and message contents.
   *
   * @param printer A Printer object that will receive log messages, or
   * null to disable message logging.
   */
public final class Looper { 
  private Printer mLogging; 
  public void setMessageLogging(@Nullable Printer printer) { 
    mLogging = printer; 
  } 
} 

public interface Printer { 
  void println(String x); 
}

public class BlockDetectByPrinter {
  
  public static void start() {
    Looper.getMainLooper().setMessageLogging(new Printer() {
      private static final String START = ">>>>> Dispatching";
      private static final String END = "<<<<< Finished";

      @Override
      public void println(String x) {
        if (x.startsWith(START)) {
          LogMonitor.getInstance().startMonitor();
        }
        if (x.startsWith(END)) {
          LogMonitor.getInstance().removeMonitor();
        }
      }
    });
  }
}

public class LogMonitor {
  private static final String TAG = "LogMonitor";
  private static LogMonitor sInstance = new LogMonitor();
  private HandlerThread mLogThread = new HandlerThread("log");
  private Handler mIoHandler;
  private static final long TIME_BLOCK = 200L;

  private LogMonitor() {
    mLogThread.start();
    mIoHandler = new Handler(mLogThread.getLooper());
  }

  private static Runnable mLogRunnable = new Runnable() {
    @Override
    public void run() {
      StringBuilder sb = new StringBuilder();
      StackTraceElement[] stackTrace = Looper.getMainLooper().getThread().getStackTrace();
      for (StackTraceElement s : stackTrace) {
        sb.append(s.toString() + "\n");
      }
      Log.e(TAG, sb.toString());
    }
  };

  public static LogMonitor getInstance() {
    return sInstance;
  }

  public boolean isMonitor() {
    return mIoHandler.hasCallbacks(mLogRunnable);
  }

  public void startMonitor() {
    mIoHandler.postDelayed(mLogRunnable, TIME_BLOCK);
  }

  public void removeMonitor() {
    mIoHandler.removeCallbacks(mLogRunnable);
  }
}

  /** {@hide} */
  public interface Observer {
    /**
     * Called right before a message is dispatched.
     *
     * <p> The token type is not specified to allow the implementation to specify its own type.
     *
     * @return a token used for collecting telemetry when dispatching a single message.
     *     The token token must be passed back exactly once to either
     *     {@link Observer#messageDispatched} or {@link Observer#dispatchingThrewException}
     *     and must not be reused again.
     *
     */
    Object messageDispatchStarting();

    /**
     * Called when a message was processed by a Handler.
     *
     * @param token Token obtained by previously calling
     *       {@link Observer#messageDispatchStarting} on the same Observer instance.
     * @param msg The message that was dispatched.
     */
    void messageDispatched(Object token, Message msg);

    /**
     * Called when an exception was thrown while processing a message.
     *
     * @param token Token obtained by previously calling
     *       {@link Observer#messageDispatchStarting} on the same Observer instance.
     * @param msg The message that was dispatched and caused an exception.
     * @param exception The exception that was thrown.
     */
    void dispatchingThrewException(Object token, Message msg, Exception exception);
  }

public class FPSFrameCallback implements Choreographer.FrameCallback {

  private static final String TAG = "FPS_TEST";
  private long mLastFrameTimeNanos = 0;
  private long mFrameIntervalNanos;

  public FPSFrameCallback(long lastFrameTimeNanos) {
    mLastFrameTimeNanos = lastFrameTimeNanos;
    // 1s 60 幀
    mFrameIntervalNanos = (long) (1000000000 / 60.0);
  }

  @Override
  public void doFrame(long frameTimeNanos) {

    //初始化時(shí)間
    if (mLastFrameTimeNanos == 0) {
      mLastFrameTimeNanos = frameTimeNanos;
    }
    final long jitterNanos = frameTimeNanos - mLastFrameTimeNanos;
    if (jitterNanos >= mFrameIntervalNanos) {
      final long skippedFrames = jitterNanos / mFrameIntervalNanos;
      if (skippedFrames > 30) {
        Log.i(TAG, "Skipped " + skippedFrames + " frames! "
            + "The application may be doing too much work on its main thread.");
      }
    }
    mLastFrameTimeNanos = frameTimeNanos;
    //注冊(cè)下一幀回調(diào)
    Choreographer.getInstance().postFrameCallback(this);
  }
}

public class MainActivity extends AppCompatActivity {
  Handler handler = new Handler(Looper.getMainLooper());

  private final Runnable runnable = new Runnable() {
    @Override
    public void run() {
      try {
        Thread.sleep(600);
        handler.postDelayed(runnable, 500);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }
  };

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Choreographer.getInstance().postFrameCallback(new FPSFrameCallback(System.nanoTime()));
    BlockDetectByPrinter.start();
  }

  @Override
  protected void onResume() {
    super.onResume();
    handler.postDelayed(runnable, 500);
  }

}