线程中断不工作 (Java Android)

Question

编辑：

我有一个带有 Runnable 的线程，如下所示。它有一个我无法弄清楚的问题：我在线程上调用 interrupt() 的一半时间（以停止它）实际上并没有终止（未捕获 InterruptedException ）。

private class DataRunnable implements Runnable {
    @Override
    public void run() {
        Log.d(TAG, "DataRunnable started");
        while (true) {
            try {
                final String currentTemperature = HeatingSystem.get("currentTemperature");
                mView.post(() -> showData(currentTemperature));
            } catch (ConnectException e) {
                mView.post(() -> showConnectionMessage());
                break;
            }
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                break;
            }
        }
        Log.d(TAG, "DataRunnable terminated");
    }
}

问题出在执行长网络操作的 HeatingSystem.get(String) 方法上。我想在那个方法的某个地方中断标志被重置但是我找不到什么语句会这样做（我没有发现它在参考文献中提到了所有涉及该方法的类，比如 HttpURLConnection).方法如下（不是我写的）

/**
 * Retrieves all data except for weekProgram
 * @param attribute_name
 *            = { "day", "time", "currentTemperature", "dayTemperature",
 *            "nightTemperature", "weekProgramState" }; Note that
 *            "weekProgram" has not been included, because it has a more
 *            complex value than a single value. Therefore the funciton
 *            getWeekProgram() is implemented which return a WeekProgram
 *            object that can be easily altered.
 */
public static String get(String attribute_name) throws ConnectException,
        IllegalArgumentException {
    // If XML File does not contain the specified attribute, than
    // throw NotFound or NotFoundArgumentException
    // You can retrieve every attribute with a single value. But for the
    // WeekProgram you need to call getWeekProgram().
    String link = "";
    boolean match = false;
    String[] valid_names = {"day", "time", "currentTemperature",
            "dayTemperature", "nightTemperature", "weekProgramState"};
    String[] tag_names = {"current_day", "time", "current_temperature",
            "day_temperature", "night_temperature", "week_program_state"};
    int i;
    for (i = 0; i < valid_names.length; i++) {
        if (attribute_name.equalsIgnoreCase(valid_names[i])) {
            match = true;
            link = HeatingSystem.BASE_ADDRESS + "/" + valid_names[i];
            break;
        }
    }

    if (match) {
        InputStream in = null;
        try {
            HttpURLConnection connect = getHttpConnection(link, "GET");
            in = connect.getInputStream();

            /**
             * For Debugging Note that when the input stream is already used
             * with this BufferedReader, then after that the XmlPullParser
             * can no longer use it. This will cause an error/exception.
             *
             * BufferedReader inn = new BufferedReader(new
             * InputStreamReader(in)); String testLine = ""; while((testLine
             * = inn.readLine()) != null) { System.out.println("Line: " +
             * testLine); }
             */
            // Set up an XML parser.
            XmlPullParser parser = Xml.newPullParser();
            parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES,
                    false);
            parser.setInput(in, "UTF-8"); // Enter the stream.
            parser.nextTag();
            parser.require(XmlPullParser.START_TAG, null, tag_names[i]);

            int eventType = parser.getEventType();

            // Find the single value.
            String value = "";
            while (eventType != XmlPullParser.END_DOCUMENT) {
                if (eventType == XmlPullParser.TEXT) {
                    value = parser.getText();
                    break;
                }
                eventType = parser.next();
            }

            return value;
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            System.out.println("FileNotFound Exception! " + e.getMessage());
            // e.printStackTrace();
        } catch (XmlPullParserException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (in != null)
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
    } else {
        // return null;
        throw new IllegalArgumentException("Invalid Input Argument: \""
                + attribute_name + "\".");
    }
    return null;
}

/**
 * Method for GET and PUT requests
 * @param link
 * @param type
 * @return
 * @throws IOException
 * @throws MalformedURLException
 * @throws UnknownHostException
 * @throws FileNotFoundException
 */
private static HttpURLConnection getHttpConnection(String link, String type)
        throws IOException, MalformedURLException, UnknownHostException,
        FileNotFoundException {
    URL url = new URL(link);
    HttpURLConnection connect = (HttpURLConnection) url.openConnection();
    connect.setReadTimeout(HeatingSystem.TIME_OUT);
    connect.setConnectTimeout(HeatingSystem.TIME_OUT);
    connect.setRequestProperty("Content-Type", "application/xml");
    connect.setRequestMethod(type);
    if (type.equalsIgnoreCase("GET")) {
        connect.setDoInput(true);
        connect.setDoOutput(false);
    } else if (type.equalsIgnoreCase("PUT")) {
        connect.setDoInput(false);
        connect.setDoOutput(true);
    }
    connect.connect();
    return connect;
}

有人知道上述方法中的什么可能导致问题吗？

如果在进入 Thread.sleep() 之前调用了 interrupt()，Thread.sleep() 也会抛出 InterruptException：Calling Thread.sleep() with *interrupted status* set? .

我查看了中断后是否达到了Thread.sleep()，确实达到了

这就是 DataRunnable 的启动和中断方式（我总是得到 "onPause called" 日志）：

@Override
public void onResume() {
    connect();
    super.onResume();
}

@Override
public void onPause() {
    Log.d(TAG, "onPause called");
    mDataThread.interrupt();
    super.onPause();
}

private void connect() {
    if (mDataThread != null && mDataThread.isAlive()) {
        Log.e(TAG, "mDataThread is alive while it shouldn't!"); // TODO: remove this for production.
    }
    setVisibleView(mLoading);
    mDataThread = new Thread(new DataRunnable());
    mDataThread.start();
}

Answer 1

您需要将 while 循环更改为：

// You'll need to change your while loop check to this for it to reliably stop when interrupting.
while(!Thread.currentThread().isInterrupted()) {
    try {
        final String currentTemperature = HeatingSystem.get("currentTemperature");
        mView.post(() -> showData(currentTemperature));
    } catch (ConnectException e) {
        mView.post(() -> showConnectionMessage());
        break;
    }

    try {
        Thread.sleep(10);
    } catch (InterruptedException e) {
        break;
    }
}

而不是while(true)。

请注意 Thread.interrupted() 和 Thread.currentThread().isInterrupted() 做不同的事情。第一个在检查后重置中断状态。后者保持状态不变。

Answer 2

过去我一直在为类似的问题而苦苦挣扎，但从未找到令人满意的解决方案。唯一对我有用的解决方法是引入一个 volatile 布尔 "stopRequested" 成员变量，该变量设置为 true 以中断 Runnable 并检查 Runnable 的 while 条件而不是线程的中断状态。

关于我的经历的不幸细节是，我从来没有能够提取一个小的可编译示例来重现这个问题。你能做到吗？如果您无法做到这一点，我很想知道您是否确定您正在使用正确的 mDataThread 实例？您可以通过记录其哈希码来验证这一点...

Answer 3

这不是真正的答案，但我不知道该把它放在哪里。通过进一步调试，我认为我遇到了奇怪的行为，并且我能够在测试中重现它 class。现在我很好奇这是否真的是我怀疑的错误行为，以及其他人是否可以重现它。我希望把它写成答案。

（将其变成一个新问题，或者实际上只是提交错误报告会更好吗？）

下面是测试 class，它必须是 Android 上的运行，因为它是关于 getInputStream() 的调用，它在 Android 上的行为不同（不知道确切原因）。在 Android 上，getInputStream() 会在被打断时抛出一个 InterruptedIOException。下面的线程循环并在一秒钟后被中断。因此，当它被中断时，异常应该由 getInputStream() 抛出并且应该使用 catch 块捕获。这有时可以正常工作，但大多数时候不会抛出异常！相反，只有中断标志被重置，因此从 interrupted==true 更改为 interrupted==false，然后被 if 捕获。 if 中的消息为我弹出。在我看来，这是错误的行为。

import java.net.HttpURLConnection;
import java.net.URL;

class InterruptTest {

InterruptTest() {
    Thread thread = new Thread(new ConnectionRunnable());
    thread.start();
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {}
    thread.interrupt();
}

private class ConnectionRunnable implements Runnable {
    @Override
    public void run() {
        while (true) {
            try {
                URL url = new URL("http://www.google.com");
                HttpURLConnection connect = (HttpURLConnection) url.openConnection();

                boolean wasInterruptedBefore = Thread.currentThread().isInterrupted();
                connect.getInputStream(); // This call seems to behave odd(ly?)
                boolean wasInterruptedAfter = Thread.currentThread().isInterrupted();

                if (wasInterruptedBefore == true && wasInterruptedAfter == false) {
                    System.out.println("Wut! Interrupted changed from true to false while no InterruptedIOException or InterruptedException was thrown");
                    break;
                }
            } catch (Exception e) {
                System.out.println(e.getClass().getName() + ": " + e.getMessage());
                break;
            }
            for (int i = 0; i < 100000; i += 1) { // Crunching
                System.out.print("");
            }
        }
        System.out.println("ConnectionThread is stopped");
    }
}
}

线程中断不工作 (Java Android)

Thread interrupt not working (Java Android)

java

multithreading

android

interrupted-exception