Java Future.isDone 返回 true，即使它不应该，这会停止程序进度

Question

我有一个 SwingWorker，它启动一个 LinkedBlockingQueue，将它传递给另一个方法（PortalDriver，下面），然后在 doInBackground() 方法中读取它。 LinkedBlockingQueue 持有自定义对象的期货（并且它肯定是正确填充的）。作为检查，我正在创建的对象（通过 ExecutorService）在构造函数的末尾有一个 println(this)，所以我知道它们何时被创建。

问题是，通过 println() 调用（在 doInBackground 和构造函数中），在 doInBackground 的 while 循环中多次成功迭代后，行

System.out.println("future.isDone before get(): " + futureListing.isDone());

打印为真，即使构造函数没有打印它已被创建（这仅通过计数就清楚了）。即使创建了其余对象，while 循环也会永久阻塞。

private class ReadSchedWorker extends SwingWorker<Void, Listing> {
    private ChromeOptions options = new ChromeOptions();
    private WebDriver driver;
    private LinkedBlockingQueue<Future<Listing>> listingQueue;
    private LoginFactory loginFactory;
    private int year;
    private int month;
    private int day;

    public ReadSchedWorker(Login mediasiteLogin, Login tmsLogin,
                           int year, int month, int day) {
        System.setProperty("webdriver.chrome.driver", "\\\\private\\Home\\Desktop\\chromedriver.exe");
        listingQueue = new LinkedBlockingQueue<>();
        loginFactory = new LoginFactory(mediasiteLogin, tmsLogin);
        this.year = year;
        this.month = month;
        this.day = day;
    }

    @Override
    protected Void doInBackground() throws Exception {
        this.options.addArguments("--disable-extensions");
        driver = new ChromeDriver(options);

        String portalUsername = loginFactory.getPortalUsername();
        String portalPassword = loginFactory.getPortalPassword();
        PortalDriver portalDriver = new PortalDriver(driver, listingQueue);
        portalDriver.getScheduleElements(portalUsername, portalPassword, year, month, day);

        while (!listingQueue.isEmpty()) {
            System.out.println("beginning");
            Future<Listing> futureListing = listingQueue.take();
            System.out.println("future.isDone before get(): " + futureListing.isDone());
            Listing listing = futureListing.get();
            System.out.println("future.isDone after get(): " + futureListing.isDone());
            System.out.println("before publish");
            publish(listing);
            System.out.println("after publish");
        }
        return null;
    }

    @Override
    protected void process(List<Listing> listings) {
        for (Listing listingItem : listings) {
            listingListModel.addElement(listingItem);
        }
    }
}

为了补全，这里是getScheduleElements，它填满了LinkedBlockingQueue：

public void getScheduleElements(String username, String password, int year, int month, int day) {
    driver.get("https://rxsecure.umaryland.edu/apps/schedules/view/?type=search&searchtype=resource&id=100&start=" +
            year + "-" + month + "-" + day + "&scope=week");
    PortalLoginPage loginPage = PageFactory.initElements(driver, PortalLoginPage.class);
    PortalScheduleEventsWeekPage scheduleEventsWeekPage = loginPage.login(username, password);
    webElementsQueue = scheduleEventsWeekPage.initEventsQueue();

    // doesn't need to be a queue...
    // this is sequential....
    // could do a parallel stream
    while (webElementsQueue.peek() != null) {
        Callable<Listing> callable = new PortalListingCallable(webElementsQueue.poll());
        Future<Listing> future = executor.submit(callable);
        listingQueue.offer(future);
    }

    executor.shutdown();
}

编辑： 我的意思的一个例子（未来没有完成，但通过 doInBackground() 中的 println()s 报告它已经完成）：

beginning
future.isDone before get(): true //the future says it done, but the object being created is below
in listing contructor: PHAR580 Pharmacy Law;Specialty Pharmacy 2;Recorded in Mediasite PH S201 2015-04-27T10:00:00.000-04:00 2015-04-27T11:50:00.000-04:00

Answer 1

打印为真，即使构造函数没有打印出它已被创建

您很可能遇到了您没有看到的异常或错误。你必须调用 Future.get() 才能看到它。

同时我建议你改变

Future<Listing> future = executor.submit(callable);

到

Future<Listing> future = executor.submit(new Callable<Listing>() {
    public Listing call() throws Throwable {
        try {
            return callable.call();
        } catch (Throwable t) {
            t.printStackTrace();
            throw t;
        }
    }
});