java - Servlet "has started a thread but failed to stop it"- Tomcat 内存泄漏

Question

Apache Tomcat 说了很多次:

The web application [/MyServlet] appears to have started a thread named [pool-61-thread-2] but has failed to stop it. This is very likely to create a memory leak.

这很危险吗？ servlet 应该能够处理 10.000 个请求/天。如何在完成后关闭线程？

class Worker {

        private final CountDownLatch startSignal;
        private final CountDownLatch doneSignal;
        private final int threadNumber;

        Worker(
                CountDownLatch startSignal,
                CountDownLatch doneSignal,
                int threadNumber
        ){

            this.startSignal = startSignal;
            this.doneSignal = doneSignal;
            this.threadNumber = threadNumber;

        }

        public String[][] getSomeStrArrArr() {

            String[][] isRs = new String[8][20];
            String[][] inRs = new String[8][20];
            String[][] iwRs = new String[8][20];

            try {

                startSignal.await();

                if (threadNumber == 1) {
                    // get String[][] result for thread number 1
                    isRs = getIS(erg1, erg2, request);

                }

                if (threadNumber == 2) {
                    // get String[][] result for thread number 2
                    inRs = getIN(search_plz, request);
                }

                if (threadNumber == 3) {
                    // get String[][] result for thread number 3
                    iwRs = getIW(erg1, erg2, request);
                }

                doneSignal.countDown();

            } catch (InterruptedException ex) {

                System.out.println(
                        "Thread number "+threadNumber+" has been interrupted."
                );

            }
            if (threadNumber == 1) {
                return isRs;
            }
            if (threadNumber == 2) {
                return inRs;
            }
            if (threadNumber == 3) {
                return iwRs;
            }
            return null;
        }


        public Callable<String[][]> getSomeCallableStrArrArr(){
            return new Callable<String[][]>() {
                public String[][] call() throws Exception {
                    return getSomeStrArrArr();
                }
            };
        }

    }

    ExecutorService pool = Executors.newFixedThreadPool(3);
    Set<Future<String[][]>> set = new HashSet<Future<String[][]>>();
    CountDownLatch startSignal = new CountDownLatch(1);
    CountDownLatch doneSignal = new CountDownLatch(3);
    for (int i=1;i<=3;i++) {
        Worker worker = new Worker(startSignal,doneSignal,i);
        Callable<String[][]> callable =
                worker.getSomeCallableStrArrArr();
        Future<String[][]> future = pool.submit(callable);
        set.add(future);
    }
    startSignal.countDown();
    try {
        doneSignal.await();

Answer 1

是的，这是一个问题。如果您的代码启动非守护线程，那么这些线程将继续工作，直到它们退出 run 方法。即使其他一切都完成了，旧的 JVM 也会在这些线程继续运行时挂起。如果您启动一个新实例，那么您可能会遇到旧线程仍在与新实例创建的线程一起工作的情况。

需要设计任务，以便它们能够响应中断(而不是吃掉异常并继续，这就是您的示例所显示的)。这意味着检查当前线程上的中断标志，并以一种有用的方式捕获 InterruptedException，从而允许任务中断其工作并在需要时重置中断标志。 ExecutorService 实现有一个 shutdownNow 方法，它会中断当前任务。

Here's an example of how to stop a thread using interruption .

确保执行器被关闭，you can handle this in a ServletContextListener .