我需要一个解决方案来正确地停止Java中的线程。
我有IndexProcessorclass，它实现了可运行接口:
public class IndexProcessor implements Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
@Override
public void run() {
boolean run = true;
while (run) {
try {
LOGGER.debug("Sleeping...");
Thread.sleep((long) 15000);
LOGGER.debug("Processing");
} catch (InterruptedException e) {
LOGGER.error("Exception", e);
run = false;
}
}
}
}
我有ServletContextListener类启动和停止线程:
public class SearchEngineContextListener implements ServletContextListener {
private static final Logger LOGGER = LoggerFactory.getLogger(SearchEngineContextListener.class);
private Thread thread = null;
@Override
public void contextInitialized(ServletContextEvent event) {
thread = new Thread(new IndexProcessor());
LOGGER.debug("Starting thread: " + thread);
thread.start();
LOGGER.debug("Background process successfully started.");
}
@Override
public void contextDestroyed(ServletContextEvent event) {
LOGGER.debug("Stopping thread: " + thread);
if (thread != null) {
thread.interrupt();
LOGGER.debug("Thread successfully stopped.");
}
}
}
但是当我关闭tomcat时，我在IndexProcessor类中得到了异常:
2012-06-09 17:04:50,671 [Thread-3] ERROR IndexProcessor Exception
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at lt.ccl.searchengine.processor.IndexProcessor.run(IndexProcessor.java:22)
at java.lang.Thread.run(Unknown Source)
我使用的是JDK 1.6。所以问题是:
我如何停止线程而不抛出任何异常?
附注:我不想使用.stop();方法，因为它已弃用。
在IndexProcessor类中，您需要一种方法来设置一个标志，该标志通知线程它将需要终止，类似于您在类作用域中使用的变量run。
当您希望停止线程时，您可以设置这个标志并在线程上调用join()并等待它完成。
通过使用volatile变量或使用getter和setter方法来确保该标志是线程安全的，这些方法与用作标志的变量同步。
public class IndexProcessor implements Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
private volatile boolean running = true;
public void terminate() {
running = false;
}
@Override
public void run() {
while (running) {
try {
LOGGER.debug("Sleeping...");
Thread.sleep((long) 15000);
LOGGER.debug("Processing");
} catch (InterruptedException e) {
LOGGER.error("Exception", e);
running = false;
}
}
}
}
然后在SearchEngineContextListener中:
public class SearchEngineContextListener implements ServletContextListener {
private static final Logger LOGGER = LoggerFactory.getLogger(SearchEngineContextListener.class);
private Thread thread = null;
private IndexProcessor runnable = null;
@Override
public void contextInitialized(ServletContextEvent event) {
runnable = new IndexProcessor();
thread = new Thread(runnable);
LOGGER.debug("Starting thread: " + thread);
thread.start();
LOGGER.debug("Background process successfully started.");
}
@Override
public void contextDestroyed(ServletContextEvent event) {
LOGGER.debug("Stopping thread: " + thread);
if (thread != null) {
runnable.terminate();
thread.join();
LOGGER.debug("Thread successfully stopped.");
}
}
}
对于同步线程，我更喜欢使用CountDownLatch，它可以帮助线程等待进程执行完成。在本例中，使用具有给定计数的CountDownLatch实例来设置工作者类。由于调用了countDown方法或达到了超时设置，await方法的调用将阻塞到当前计数为零。这种方法允许立即中断线程，而不需要等待指定的等待时间过去:
public class IndexProcessor implements Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
private final CountDownLatch countdownlatch;
public IndexProcessor(CountDownLatch countdownlatch) {
this.countdownlatch = countdownlatch;
}
public void run() {
try {
while (!countdownlatch.await(15000, TimeUnit.MILLISECONDS)) {
LOGGER.debug("Processing...");
}
} catch (InterruptedException e) {
LOGGER.error("Exception", e);
run = false;
}
}
}
当你想要完成另一个线程的执行时，在CountDownLatch上执行countDown，并将该线程加入主线程:
public class SearchEngineContextListener implements ServletContextListener {
private static final Logger LOGGER = LoggerFactory.getLogger(SearchEngineContextListener.class);
private Thread thread = null;
private IndexProcessor runnable = null;
private CountDownLatch countdownLatch = null;
@Override
public void contextInitialized(ServletContextEvent event) {
countdownLatch = new CountDownLatch(1);
Thread thread = new Thread(new IndexProcessor(countdownLatch));
LOGGER.debug("Starting thread: " + thread);
thread.start();
LOGGER.debug("Background process successfully started.");
}
@Override
public void contextDestroyed(ServletContextEvent event) {
LOGGER.debug("Stopping thread: " + thread);
if (countdownLatch != null)
{
countdownLatch.countDown();
}
if (thread != null) {
try {
thread.join();
} catch (InterruptedException e) {
LOGGER.error("Exception", e);
}
LOGGER.debug("Thread successfully stopped.");
}
}
}
在IndexProcessor类中，您需要一种方法来设置一个标志，该标志通知线程它将需要终止，类似于您在类作用域中使用的变量run。
当您希望停止线程时，您可以设置这个标志并在线程上调用join()并等待它完成。
通过使用volatile变量或使用getter和setter方法来确保该标志是线程安全的，这些方法与用作标志的变量同步。
public class IndexProcessor implements Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
private volatile boolean running = true;
public void terminate() {
running = false;
}
@Override
public void run() {
while (running) {
try {
LOGGER.debug("Sleeping...");
Thread.sleep((long) 15000);
LOGGER.debug("Processing");
} catch (InterruptedException e) {
LOGGER.error("Exception", e);
running = false;
}
}
}
}
然后在SearchEngineContextListener中:
public class SearchEngineContextListener implements ServletContextListener {
private static final Logger LOGGER = LoggerFactory.getLogger(SearchEngineContextListener.class);
private Thread thread = null;
private IndexProcessor runnable = null;
@Override
public void contextInitialized(ServletContextEvent event) {
runnable = new IndexProcessor();
thread = new Thread(runnable);
LOGGER.debug("Starting thread: " + thread);
thread.start();
LOGGER.debug("Background process successfully started.");
}
@Override
public void contextDestroyed(ServletContextEvent event) {
LOGGER.debug("Stopping thread: " + thread);
if (thread != null) {
runnable.terminate();
thread.join();
LOGGER.debug("Thread successfully stopped.");
}
}
}
您应该始终通过检查run()循环中的标志(如果有的话)来结束线程。
你的线程应该是这样的:
public class IndexProcessor implements Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
private volatile boolean execute;
@Override
public void run() {
this.execute = true;
while (this.execute) {
try {
LOGGER.debug("Sleeping...");
Thread.sleep((long) 15000);
LOGGER.debug("Processing");
} catch (InterruptedException e) {
LOGGER.error("Exception", e);
this.execute = false;
}
}
}
public void stopExecuting() {
this.execute = false;
}
}
然后你可以通过调用thread. stopexecution()结束线程。这样线程就干净地结束了，但这需要15秒(因为你在睡觉)。
如果确实非常紧急，您仍然可以调用thread.interrupt() -但首选方法应该始终是检查标志。
为了避免等待15秒，你可以像这样分割睡眠:
...
try {
LOGGER.debug("Sleeping...");
for (int i = 0; (i < 150) && this.execute; i++) {
Thread.sleep((long) 100);
}
LOGGER.debug("Processing");
} catch (InterruptedException e) {
...
一些补充信息。
Java文档中都建议使用标志和中断。
https://docs.oracle.com/javase/8/docs/technotes/guides/concurrency/threadPrimitiveDeprecation.html
private volatile Thread blinker;
public void stop() {
blinker = null;
}
public void run() {
Thread thisThread = Thread.currentThread();
while (blinker == thisThread) {
try {
Thread.sleep(interval);
} catch (InterruptedException e){
}
repaint();
}
}
对于需要长时间等待的线程(例如，等待输入)，使用thread .interrupt
public void stop() {
Thread moribund = waiter;
waiter = null;
moribund.interrupt();
}
Brian Goetz在他的书中建议使用Thread.currentThread(). isinterrupted()标志和interrupt()方法来取消。
阻塞库方法(如sleep()和wait())尝试检测线程何时被中断并提前返回。它们通过清除中断状态并抛出InterruptedException来响应中断，这表明阻塞操作由于中断而提前完成。
JVM不保证阻塞方法检测中断的速度有多快，但在实践中，检测中断的速度相当快。
class PrimeProducer extends Thread {
private final BlockingQueue<BigInteger> queue;
PrimeProducer(BlockingQueue<BigInteger> queue) {
this.queue = queue;
}
public void run() {
try {
BigInteger p = BigInteger.ONE;
while (!Thread.currentThread().isInterrupted()) {
queue.put(p = p.nextProbablePrime()); // blocking operation
}
} catch (InterruptedException consumed) {
// allow thread to exit
}
// any code here will still be executed
}
public void cancel() {
interrupt();
}
}
如果您将任何代码放在catch块之后，当我们吞咽InterruptedException以优雅地退出run()时，它仍然会被执行。
简单介绍一下interrupt()的工作原理。
如果在非阻塞的线程上调用interrupt，则interrupt()不会在run()内部引起InterruptedException，而只是将isInterrupted标志更改为true，线程将继续工作，直到到达thread . currentthread ().isInterrupted()检查并退出run()。
如果在阻塞的线程上调用interrupt (sleep()或wait()被调用，在我们的例子中，它是put()可能阻塞线程)，那么isInterrupted将被设置为false，并且在put()中抛出InterruptedException。
