Android/Java 线程同步：while(true){} 导致阻塞

Question

我正在尝试更好地了解我的 Android 应用程序中线程的行为。出于某种原因，当我在我的一个工作线程中使用 while(true) 时，该线程的 run 方法中在 while(true) 循环之前顺序存在的代码永远不会执行。需要明确的是，我不确定代码（toast 消息）是否实际上没有执行，或者 Android 操作系统处理线程同步的方式是否导致我的 Toast 消息不显示。这种行为似乎是某种阻塞，但我无法弄清楚为什么会发生这种情况。

我的应用程序使用 3 个线程：UI 线程（Android 应用程序中的默认/主线程）、一个在运行时从设备的 USB 端口无限读取数据的线程，以及一个通过来自 USB 的消息处理这些数据的线程-阅读线程。问题似乎出现在我的 USBController 类中。当我注释掉我的无限 while 循环时，循环开始之前的所有 Toast 消息都显示得很好。 当我不注释掉我的 while(true) 时，不会显示任何 TOAST 消息！我对此感到很困惑，我认为我误解了 Android 操作系统线程处理的一些基本知识。即使while循环会导致阻塞，我不认为这是因为它驻留在工作线程中，为什么不会触发while循环之前发生的toast消息？这是同步问题？我是否误用了 Android 的 Handler-Looper 系统？

代码如下。注意：我已经包含了主要活动的相关部分和整个 USBController 类。我对这个类的实现很大程度上依赖于mik3y/usb-serial-for-android 中的 USB 转串行库。我认为没有必要，但我已经包含了包含我的第三个线程 SensorDataBuffer 的类，它从线程 UsbController 接收消息。

UsbController.java

    public class UsbController extends Thread{
    ...
    @Override
    public void run() {
        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_DEFAULT); //sets thread to default queing priority
        Looper.prepare();
        Toast.makeText(mContext.getApplicationContext(), "Hello from UsbController's run method!", Toast.LENGTH_SHORT).show();

        // **********************USB otg*******************************
        //Obtain permission to use Android device's USB intent
        PendingIntent mPermissionIntent;
        mPermissionIntent = PendingIntent.getBroadcast(mContext, 0, new Intent(ACTION_USB_PERMISSION), 0);

        // Find all available drivers from attached devices.
        ProbeTable customTable = new ProbeTable();
        customTable.addProduct(0x03EB, 0x2044, CdcAcmSerialDriver.class);                 
        UsbManager manager = (UsbManager) mContext.getSystemService(Context.USB_SERVICE);
        UsbSerialProber prober = new UsbSerialProber(customTable);
        List<UsbSerialDriver> availableDrivers = prober.findAllDrivers(manager);

        if (availableDrivers.isEmpty()) {
            Toast.makeText(mContext.getApplicationContext(), "No available USB drivers found",Toast.LENGTH_SHORT).show(); // Toast message for debugging
        }
        else {                                                  // open connection to first avail. driver
            UsbSerialDriver driver = availableDrivers.get(0);
            Toast.makeText(mContext.getApplicationContext(), "Driver found",Toast.LENGTH_SHORT).show(); // Toast message for debugging
            UsbDeviceConnection connection = manager.openDevice(driver.getDevice());
            Toast.makeText(mContext.getApplicationContext(), "Device Driver Opened",Toast.LENGTH_SHORT).show(); // Toast message for debugging
            if (connection == null) {           // You probably need to call UsbManager.requestPermission(driver.getDevice(), ..)
                Toast.makeText(mContext.getApplicationContext(),"Connection to device not allowed, need permissions",Toast.LENGTH_LONG).show();
                manager.requestPermission(driver.getDevice(),mPermissionIntent);  //conn test
                if (manager.hasPermission(driver.getDevice())==true){
                    Toast.makeText(mContext.getApplicationContext(),"Permissions granted",Toast.LENGTH_SHORT).show();
                }
            }
            else {                      // Read some data! Most have just one port (port 0).
                List<UsbSerialPort> myPortList = driver.getPorts();
                UsbSerialPort port = myPortList.get(0);
                Toast.makeText(mContext.getApplicationContext(),"USB OTG Connection Established",Toast.LENGTH_SHORT).show();
                try {
                    port.open(connection);
                    port.setParameters(9600, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE); // sets baud rate,databits, stopbits, & parity
                    port.setDTR(true);                 //necessary to make Arduino Micro begin running it's program
                    Toast.makeText(mContext.getApplicationContext(),"port opened, parameters set, DTR set",Toast.LENGTH_SHORT).show();
                    byte buffer[] = new byte[16];      
                    String incompPacket = "";
                    Toast.makeText(mContext.getApplicationContext(), "hi again!"), Toast.LENGTH_LONG).show();
                    while (true){                  //continuous loop to read data
                        numBytesRead = port.read(buffer, 100);          
                        arduinoData = new String(buffer, "US-ASCII");
                        String raw = arduinoData.substring(0, numBytesRead);
                        if (numBytesRead > 0) {
                            ...
                        }
                    }
                } catch (IOException e) {
                    Toast.makeText(mContext, e.getMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        }
        Looper.loop(); 
    }
}

MainActivity.java

...
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        //Multi-threading
        //Create thread to handle incoming data from USB Controller thread
        SensorDataBuffer pressureDataBuffer = new SensorDataBuffer(MainActivity.this);
        Thread bufferThread = new Thread(pressureDataBuffer);
        bufferThread.start();

        //Create USB Serial Worker thread which will continuously receive data
        UsbController serialDataLink = new UsbController(PlayFrets.this);
        Thread sensorMonitorThread = new Thread(serialDataLink);
        sensorMonitorThread.start();
        //Toast.makeText(this, "USB Controller thread started", Toast.LENGTH_SHORT).show();

        //Build GUI
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);           //Removes action bar from display
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);  //Removes status bar from display

        //Create AsyncTask to load the note files. A splash screen will be displayed while task is executing
        new AsyncTask_NoteFileLoader(this).execute();
        }
...

SensorDataBuffer.java

public class SensorDataBuffer extends Thread{

    //Handler subclass which accepts messages one by one in
    //the main activitiy's FIFO message que called a "Looper"
    //The worker thread, sensorMonitor, runs UsbController in parallel
    //with the UI thread and continuously formats and sends pressure sensor
    //values read from the microcontroller to the Handler which updates the
    //corresponding pressure state logic variables in the UI thread.
    public void run(){
        android.os.Process.setThreadPriority(Process.THREAD_PRIORITY_URGENT_AUDIO); //TODO:priority was previously more favorable, test this to ensure UI doesn't lag
        Looper.prepare(); //create MessageQue to receive messages from USB Controller thread
        UsbController.setHandler(bufferHandler);

        bufferHandler = new Handler(Looper.myLooper()) {
                //do stuff
        };
        Looper.loop();
    }
}

Answer 1

改用 HandlerThreads、Handlers 和 Runnables 怎么样？使您的代码更简洁，更易于维护。

在你的 onCreate() 中创建几个：

HandlerThread usbThread = new HandlerThread("USBController");
usbThread.start();
usbHandler = new Handler(usbThread.getLooper());

HandlerThread sensorThread = new HandlerThread("SensorDataBuffer");
sensorThread.start();
sensorHandler = new Handler(sensorThread.getLooper());

然后你创建你的 Runnables 并将它们发布到处理程序

usbHandler.post(new Runnable(){
    run(){
        //....
        numBytesRead = port.read(buffer, 100);
            if (numBytesRead > 0) {
               sensorHandler.post(new Runnable(){run(){//doSomething}});
            }
        //....
        if(isStillRunning)
            usbHandler.post(this);
    }
});

您可以让可运行的帖子本身，它会永远运行。您可以在内部将 runnables 发布到其他处理程序（如主线程处理程序）以显示您的 Toast。