处理程序 post 执行队列的顺序不正确

Question

我正在开发 android 与蓝牙 BLE 设备通信的应用程序（使用专门为我们的产品开发的自定义协议）。

连接到设备后我有回调public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) 每次设备要向我发送数据时都会触发。在应用程序架构中，我们有操作（例如 getDeviceStatus()），协议按以下方式工作：phone 连接到设备 -> 握手 -> 发送命令（作为字节） -> 设备响应命令（ ok/not ok) -> 现在设备开始发送 X byte[] 块。所以为了确保我们以正确的顺序处理数据并且不会因为我添加的不同线程而变得混乱 HandlerThread:

HandlerThread handlerThread = new HandlerThread("ActionHandlerThread");
      handlerThread.start();
      Looper looper = handlerThread.getLooper();
      mHandler = new Handler(looper);

每次设备发送数据时我都会调用

@Override
 public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
    mHandler.post(() -> {
        mListener.onCharacteristicChanged(gatt, characteristic);
        }
    );  
 }

和 mListener 将数据发送给其他 class，后者检查到达的数据类型和预期的数据类型。如果我每次调用 post() 时都理解正确，则新任务将添加到处理程序的循环程序中，并且应该以与添加它们相同的顺序处理任务，但是当我运行日志中的应用程序时，我会看到回调正确触发并且 post() 以正确的顺序调用，但随后的处理以错误的顺序发生。例如，应用程序期望收到确认命令，但数据已经到达，但这是不可能的，因为数据不能在确认之前到达。我创建 HandlerThread 的主要原因是为了确保使用 BLE 的整个操作将运行在单线程上进行，而不用担心同步问题，但现在看来我确实遇到了同步问题。我是否想念一些逻辑或对 HandlerThread 工作的理解。

我只用计时器和计数器进行的一些测试，我们可以看到当间隔小到 1 毫秒时，并非所有任务都打印在 post 中：

5 毫秒的间隔：

2019-01-30 21:33:31.531 27991-27991/? D/ThreadTest: Thread before Thread[main,5,main]
2019-01-30 21:33:31.532 27991-28036/? D/ThreadTest: Counter : 1 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.532 27991-28035/? D/ThreadTest: Counter : 1 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.537 27991-28036/? D/ThreadTest: Counter : 2 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.538 27991-28035/? D/ThreadTest: Counter : 2 , inside post Thread[MyTestThread,5,main]
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2019-01-30 21:33:31.543 27991-28035/? D/ThreadTest: Counter : 3 , inside post Thread[MyTestThread,5,main]
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2019-01-30 21:33:31.704 27991-28036/? D/ThreadTest: Counter : 34 , Thread[Timer-0,5,main]
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2019-01-30 21:33:31.715 27991-28036/? D/ThreadTest: Counter : 36 , Thread[Timer-0,5,main]
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2019-01-30 21:33:31.719 27991-28036/? D/ThreadTest: Counter : 37 , Thread[Timer-0,5,main]
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2019-01-30 21:33:31.724 27991-28036/? D/ThreadTest: Counter : 38 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.724 27991-28035/? D/ThreadTest: Counter : 38 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.730 27991-28036/? D/ThreadTest: Counter : 39 , Thread[Timer-0,5,main]
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2019-01-30 21:33:31.735 27991-28036/? D/ThreadTest: Counter : 40 , Thread[Timer-0,5,main]
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2019-01-30 21:33:31.750 27991-28035/? D/ThreadTest: Counter : 43 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.756 27991-28036/? D/ThreadTest: Counter : 44 , Thread[Timer-0,5,main]
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2019-01-30 21:33:31.760 27991-28036/? D/ThreadTest: Counter : 45 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.760 27991-28035/? D/ThreadTest: Counter : 45 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.765 27991-28036/? D/ThreadTest: Counter : 46 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.765 27991-28035/? D/ThreadTest: Counter : 46 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.771 27991-28036/? D/ThreadTest: Counter : 47 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.771 27991-28035/? D/ThreadTest: Counter : 47 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.775 27991-28036/? D/ThreadTest: Counter : 48 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.775 27991-28035/? D/ThreadTest: Counter : 48 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:33:31.780 27991-28036/? D/ThreadTest: Counter : 49 , Thread[Timer-0,5,main]
2019-01-30 21:33:31.780 27991-28035/? D/ThreadTest: Counter : 49 , inside post Thread[MyTestThread,5,main]
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2019-01-30 21:33:31.786 27991-28035/? D/ThreadTest: Counter : 50 , inside post Thread[MyTestThread,5,main]

1 毫秒的间隔：

2019-01-30 21:32:57.104 27831-27831/? D/ThreadTest: Thread before Thread[main,5,main]
2019-01-30 21:32:57.105 27831-27866/? D/ThreadTest: Counter : 1 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.106 27831-27865/? D/ThreadTest: Counter : 1 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.107 27831-27866/? D/ThreadTest: Counter : 2 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.107 27831-27865/? D/ThreadTest: Counter : 2 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.109 27831-27866/? D/ThreadTest: Counter : 3 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.110 27831-27865/? D/ThreadTest: Counter : 3 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.111 27831-27866/? D/ThreadTest: Counter : 4 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.111 27831-27865/? D/ThreadTest: Counter : 4 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.112 27831-27866/? D/ThreadTest: Counter : 5 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.112 27831-27865/? D/ThreadTest: Counter : 5 , inside post Thread[MyTestThread,5,main]
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2019-01-30 21:32:57.152 27831-27865/? D/ThreadTest: Counter : 40 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.153 27831-27866/? D/ThreadTest: Counter : 41 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.154 27831-27866/? D/ThreadTest: Counter : 42 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.154 27831-27865/? D/ThreadTest: Counter : 42 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.154 27831-27865/? D/ThreadTest: Counter : 42 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.155 27831-27866/? D/ThreadTest: Counter : 43 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.155 27831-27865/? D/ThreadTest: Counter : 43 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.156 27831-27866/? D/ThreadTest: Counter : 44 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.156 27831-27865/? D/ThreadTest: Counter : 44 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.157 27831-27866/? D/ThreadTest: Counter : 45 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.158 27831-27865/? D/ThreadTest: Counter : 45 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.159 27831-27866/? D/ThreadTest: Counter : 46 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.159 27831-27865/? D/ThreadTest: Counter : 46 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.160 27831-27866/? D/ThreadTest: Counter : 47 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.160 27831-27865/? D/ThreadTest: Counter : 47 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.161 27831-27866/? D/ThreadTest: Counter : 48 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.161 27831-27865/? D/ThreadTest: Counter : 48 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.163 27831-27866/? D/ThreadTest: Counter : 49 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.163 27831-27866/? D/ThreadTest: Counter : 50 , Thread[Timer-0,5,main]
2019-01-30 21:32:57.163 27831-27865/? D/ThreadTest: Counter : 50 , inside post Thread[MyTestThread,5,main]
2019-01-30 21:32:57.163 27831-27865/? D/ThreadTest: Counter : 50 , inside post Thread[MyTestThread,5,main]

测试代码：

private fun handlerThreadTest() {
    val handlerThread = HandlerThread("MyTestThread")
    handlerThread.start()

    val handler = Handler(handlerThread.looper)

    Log.d("ThreadTest", "Thread before ${Thread.currentThread()}")
    var i = 0
    val timerObj = Timer()
    val timerTaskObj = object : TimerTask() {
      override fun run() {
        i++
        //perform your action here
        Log.d("ThreadTest", "Counter : $i , ${Thread.currentThread()}")
        handler.post {
          Log.d("ThreadTest", "Counter : $i , inside post ${Thread.currentThread()}")
          if (i == 50)
            timerObj.cancel()
        }
      }
    }

    timerObj.schedule(timerTaskObj, 0, 5)

  }

Answer 1

您的代码中有错误。在 post 您的 Runnable 之前，您需要从特性中提取值。否则以后Runnable运行提取值的时候，就是最新的。

Chromium 中的 Web 蓝牙实现犯了同样的错误。参见 https://bugs.chromium.org/p/chromium/issues/detail?id=647673&desc=2。

但还要注意，在较新版本的 Android 中，您可以直接在 connectGatt 中设置处理程序。

处理程序 post 执行队列的顺序不正确

Handler post execute queue not in correct order

android

handler

threadpool

bluetooth-lowenergy