为什么我的ArrayBlockingQueue在列入列表后导致空队列？

Question

这是我第一次在StackOverflow上提出问题。 我遇到的问题如下：

我有一个制作人和消费者类。 在Producer类中，我逐行读取文件，并将这些文本行放在字符串列表中。 当列表具有x行数时。 此列表将添加到ArrayBlockingQueue。 我有一个在主线程中启动的生产者线程。 除此之外，我开始使用几个Consumer线程。 Consumer线程从队列中获取一个项目，该项目应该是一个列表，并遍历此行列表以查找特定单词。 当找到该单词时，它会递增计数变量。

发生的事情是当Consumer从队列中获取一个项目时，它表示它是空的。 我无法弄清楚为什么，因为我的制作人当然应该将它添加到队列中。

我的代码看起来像这样：

消费者阶层：

public static class Consumer implements Callable<Integer> {

    int count = 0;

    @Override
    public Integer call() throws Exception {
        List<String> list = new ArrayList<>();
        list = arrayBlockingQueueInput.take();
        do {
            if (!list.isEmpty()){
                for (int i = 0; i < arrayBlockingQueueInput.take().size(); i++) {
                    for (String element : list.get(i).split(" ")) {
                        if (element.equalsIgnoreCase(findWord)) {
                            count++;
                        }
                    }
                }
            } else {
                arrayBlockingQueueInput.put(list);
            }
        } while (list.get(0) != "HALT");
        return count;
    }
}

制片人类：

public static class Producer implements Runnable {

    @Override
    public void run() {
        try {
            FileReader file = new FileReader("src/testText.txt");
            BufferedReader br = new BufferedReader(file);

            while ((textLine = br.readLine()) != null) {

                if (textLine.isEmpty()) {
                    continue;
                }

                /* Remove punctuation from the text, except of punctuation that is useful for certain words.
                * Examples of these words are don't or re-enter */
                textLine = textLine.replaceAll("[[\\W]&&[^']&&[^-]]", " ");

                /* Replace all double whitespaces with single whitespaces.
                * We will split the text on these whitespaces later */
                textLine = textLine.replaceAll("\\s\\s+", " ");

                textLine = textLine.replaceAll("\\n", "").replaceAll("\\r", "");

                if (results.isEmpty()) {
                    results.add(textLine);
                    continue;
                }
                if (results.size() <= SIZE) {
                    results.add(textLine);
                    if (results.size() == SIZE) {
                        if (arrayBlockingQueueInput.size() == 14){
                            List<String> list = new ArrayList<String>();
                            list.add(HALT);
                            arrayBlockingQueueInput.put(list);
                        } else{
                            arrayBlockingQueueInput.put(results);
                            results.clear();
                        }
                    }
                }
            }
            /* Count the remaining words in the list
             *  (last lines of the file do perhaps not fill up until the given SIZE, therefore need to be counted here)
             *  Fill the list with empty items if the size of the list does not match with the given SIZE */
            while (results.size() != SIZE) {
                results.add("");
            }
            arrayBlockingQueueInput.put(results);
            List<String> list = new ArrayList<String>();
            list.add(HALT);
            arrayBlockingQueueInput.put(list);
            results.clear();
        } catch (InterruptedException e) {
            producerIsRunning = false;
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

主类：

public void main() throws IOException, InterruptedException {
    System.out.println("Enter the word you want to find: ");
    Scanner scan = new Scanner(System.in);
    findWord = scan.nextLine();

    System.out.println("Starting...");
    long startTime = System.currentTimeMillis();
    Thread producer = new Thread(new Producer());
    producer.start();
    ExecutorService executorService = Executors.newFixedThreadPool(CORE);

    List<Future<Integer>> futureResults = new ArrayList<Future<Integer>>();

    for (int i = 0; i < CORE; i++) {
        futureResults.add(executorService.submit(new Consumer()));
    }

    executorService.shutdown();

    for (Future<Integer> result : futureResults) {
        try {
            wordsInText += result.get();
        } catch (ExecutionException | InterruptedException e) {
            e.printStackTrace();
        }
    }

    producer.join();

    long stopTime = System.currentTimeMillis();

    System.out.println("The word " + findWord + " appears " + wordsInText + " times in the given text");

    System.out.println("Elapsed time was " + (stopTime - startTime) + " milliseconds.");
}

任何人都可以解释为什么会这样吗？ 我想补充一点，我们尝试使用毒丸来通知消费者生产者是在HALT上。

要回答这个问题我们为什么要这样做呢？ 对于学校，我们尝试并行化某个编程问题。 我们选择的问题是字符串匹配。 我们首先制作了串行解决方案和并行解决方案。 对于下一个任务，我们必须改进我们的并行解决方案，我们的老师告诉我们这是一种方法。

提前致谢！

缺口

Answer 1

您将列表添加到队列并清除它：

arrayBlockingQueueInput.put(results);
results.clear();

您需要执行以下操作以将列表副本添加到队列中，以便clear()不会清除队列中的列表：

arrayBlockingQueueInput.put(new ArrayList<String>(results));
results.clear();

Answer 2

在老师的帮助下，他帮我们找到了问题。 有两个错误。 一个是生产者类。 我有代码在主while循环中发出生产者的HALT信号。 这不应该做。

除此之外，我在Do-While之前在Consumer类中执行的.take（）应该在do-while循环中完成。

正确的代码如下所示：

消费者阶层：

public static class Consumer implements Callable<Integer> {

    int count = 0;

    @Override
    public Integer call() throws Exception {
        List<String> list = new ArrayList<>();
        do {
            list = arrayBlockingQueueInput.take();
            if (!list.get(0).equals(HALT)){
                for (int i = 0; i < list.size(); i++) {
                    for (String element : list.get(i).split(" ")) {
                        if (element.equalsIgnoreCase(findWord)) {
                            count++;
                        }
                    }
                }
            } else {
                arrayBlockingQueueInput.put(list);
            }
        } while (!list.get(0).equals(HALT));
        return count;
    }
}

制片人类：

public static class Producer implements Runnable {

    @Override
    public void run() {
        try {
            FileReader file = new FileReader("src/testText.txt");
            BufferedReader br = new BufferedReader(file);

            while ((textLine = br.readLine()) != null) {

                if (textLine.isEmpty()) {
                    continue;
                }

                /* Remove punctuation from the text, except of punctuation that is useful for certain words.
                * Examples of these words are don't or re-enter */
                textLine = textLine.replaceAll("[[\\W]&&[^']&&[^-]]", " ");

                /* Replace all double whitespaces with single whitespaces.
                * We will split the text on these whitespaces later */
                textLine = textLine.replaceAll("\\s\\s+", " ");

                textLine = textLine.replaceAll("\\n", "").replaceAll("\\r", "");

                if (results.isEmpty()) {
                    results.add(textLine);
                    continue;
                }
                if (results.size() <= SIZE) {
                    results.add(textLine);
                    if (results.size() == SIZE) {
                        arrayBlockingQueueInput.put(new ArrayList<String>(results));
                        results.clear();
                    }
                }
            }
            /* Count the remaining words in the list
             *  (last lines of the file do perhaps not fill up until the given SIZE, therefore need to be counted here)
             *  Fill the list with empty items if the size of the list does not match with the given SIZE */
            while (results.size() != SIZE) {
                results.add("");
            }
            arrayBlockingQueueInput.put(new ArrayList<String>(results));
            List<String> list = new ArrayList<String>();
            list.add(HALT);
            arrayBlockingQueueInput.put(list);
            results.clear();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

主要课程：

public void main() throws IOException, InterruptedException {
    System.out.println("Enter the word you want to find: ");
    Scanner scan = new Scanner(System.in);
    findWord = scan.nextLine();

    System.out.println("Starting...");
    long startTime = System.currentTimeMillis();
    Thread producer = new Thread(new Producer());
    producer.start();
    ExecutorService executorService = Executors.newFixedThreadPool(CORE);

    List<Future<Integer>> futureResults = new ArrayList<Future<Integer>>();

    for (int i = 0; i < CORE; i++) {
        futureResults.add(executorService.submit(new Consumer()));
    }

    executorService.shutdown();

    for (Future<Integer> result : futureResults) {
        try {
            wordsInText += result.get();
        } catch (ExecutionException | InterruptedException e) {
            e.printStackTrace();
        }
    }

    producer.join();

    long stopTime = System.currentTimeMillis();

    System.out.println("The word " + findWord + " appears " + wordsInText + " times in the given text");

    System.out.println("Elapsed time was " + (stopTime - startTime) + " milliseconds.");
}

感谢@Ivan帮助我使用.clear方法调用结果。 没有这个，代码解决方案就不起作用了。