java - 我们如何知道 threadPoolExecutor 已经执行完毕

Question

我有一个向 MQ 发送消息的父线程，它为工作线程管理一个 ThreadPoolExecutor，工作线程监听 MQ 并将消息写入输出文件。我管理一个大小为 5 的线程池。因此，当我运行我的程序时，我有 5 个包含消息的文件。一切正常，直到这里。我现在需要将这 5 个文件合并到我的父线程中。

我如何知道 ThreadPoolExecutor 已完成处理以便我可以开始合并文件。

public class ParentThread {
    private MessageSender messageSender;
    private MessageReciever messageReciever;
    private Queue jmsQueue;
    private Queue jmsReplyQueue;
    ExecutorService exec = Executors.newFixedThreadPool(5);

    public void sendMessages() {
        System.out.println("Sending");
        File xmlFile = new File("c:/filename.txt");
        List<String> lines = null;
        try {
            lines = FileUtils.readLines(xmlFile, null);
        } catch (IOException e) {
            e.printStackTrace();
        }
        for (String line : lines){
            messageSender.sendMessage(line, this.jmsQueue, this.jmsReplyQueue);
        }
        int count = 0;
        while (count < 5) {
            messageSender.sendMessage("STOP", this.jmsQueue, this.jmsReplyQueue);
            count++;
        }

    }

    public void listenMessages() {
        long finishDate = new Date().getTime();
        for (int i = 0; i < 5; i++) {
            Worker worker = new Worker(i, this.messageReciever, this.jmsReplyQueue);
            exec.execute(worker);
        }
        exec.shutdown();

        if(exec.isTerminated()){ //PROBLEM is HERE. Control Never gets here.
            long currenttime = new Date().getTime() - finishDate;
            System.out.println("time taken: "+currenttime);
            mergeFiles();
        }
    }
}

这是我的 worker 类(Class)

public class Worker implements Runnable {

    private boolean stop = false;
    private MessageReciever messageReciever;
    private Queue jmsReplyQueue;
    private int processId;
    private int count = 0;

    private String message;
    private File outputFile;
    private FileWriter outputFileWriter;

    public Worker(int processId, MessageReciever messageReciever,
            Queue jmsReplyQueue) {
        this.processId = processId;
        this.messageReciever = messageReciever;
        this.jmsReplyQueue = jmsReplyQueue;
    }

    public void run() {
        openOutputFile();
        listenMessages();
    }


    private void listenMessages() {
        while (!stop) {
            String message = messageReciever.receiveMessage(null,this.jmsReplyQueue);
            count++;
            String s = "message: " + message + " Recieved by: "
                    + processId + " Total recieved: " + count;
            System.out.println(s);
            writeOutputFile(s);
            if (StringUtils.isNotEmpty(message) && message.equals("STOP")) {
                stop = true;
            }
        }
    }

    private void openOutputFile() {
        try {
            outputFile = new File("C:/mahi/Test", "file." + processId);
            outputFileWriter = new FileWriter(outputFile);
        } catch (IOException e) {
            System.out.println("Exception while opening file");
            stop = true;
        }
    }

    private void writeOutputFile(String message) {
        try {
            outputFileWriter.write(message);
            outputFileWriter.flush();
        } catch (IOException e) {
            System.out.println("Exception while writing to file");
            stop = true;
        }
    }
}

我如何知道 ThreadPool 何时完成处理以便我可以进行其他清理工作？

谢谢

Answer 1

如果您的 Worker 类实现了 Callable 而不是 Runnable，那么您将能够通过使用 Future 对象来查看线程何时完成，以查看 Thread 是否返回了一些结果(例如， boolean 值会告诉您它是否已完成执行与否)。

看看下面“8. Futures and Callables”部分 @ 网站，它正是我需要的东西: http://www.vogella.com/articles/JavaConcurrency/article.html

编辑:所以在所有 Future 表明它们各自的 Callable 执行完成后，可以安全地假设您的执行者已经完成执行并且可以手动关闭/终止。