Question

我正在尝试准备简单的程序，它允许用户创建很少的并发工作任务。没什么特别的。每个任务从值1开始，并在达到最大值时添加另一个任务（每个任务获得不同的最大值）。然后任务通知，已达到指定值并停止。所有任务必须包含在ArrayList中，我所做的。我需要提供允许（在每个时刻）

的方法

检查任务的状态
检查任务结果
单独结束任务，或全部结束
显示列表，其中包含所有任务（名称，值，状态）

我宁愿避免使用gui，因为我的教授并不需要。我已经参与，但我不知道如何打印列表的所有元素（TASK_LIST）并停止个别任务。

MAIN.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {

  public static void main(String[] args) {

    ExecutorService exec = Executors.newCachedThreadPool();

    Task t1 = new Task("Task 1", 2);
    Task t2 = new Task("Task 2", 20);
    Task t3 = new Task("Task 3", 5);

    exec.execute(t1);
    exec.execute(t2);
    exec.execute(t3);

    //showTASK_LIST();

  }
}

TASK.java

    import java.util.ArrayList;
    import java.util.List;

    class Task implements Runnable {
        String TASK_NAME;
        int TASK_RESULT;
        int TASK_GOAL;
        String TASK_STATUS;
        static List<Task> TASK_LIST = new ArrayList<Task>();

        public Task(String name, int goal) {
            this.TASK_NAME = name;
            this.TASK_GOAL = goal;
            this.TASK_STATUS = "INACTIVE";
            TASK_LIST.add(this);
        }

        public void run() {
            TASK_STATUS="ACTIVE";
            System.out.println(TASK_NAME + " starts.");
            while (TASK_RESULT != TASK_GOAL){
                //if (Thread.currentThread().isInterrupted()) return;
                TASK_RESULT++;
                System.out.println(TASK_NAME + " " + TASK_RESULT);
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                Thread.yield();

            }
            System.out.println("===========================================\n" + 
                                TASK_NAME + " has been completed. Final result = " + TASK_GOAL +
                                "\n===========================================" );
            setTASK_STATUS("COMPLETED");
            System.out.println(TASK_LIST.size());


        }

        //Method to check current result
        public int getTASK_RESULT() {
            return TASK_RESULT;
        }

        //Method to check current status
        public String getTASK_STATUS() {
            return TASK_STATUS;
        }

        //Method to change result
        public void setTASK_STATUS(String status) {
            TASK_STATUS = status;
        }

        //This part doesnt work
        public showTASK_LIST(){
            for(int i = 0; i <= TASK_LIST.size(); i++){
                System.out.println(TASK_LIST.get(i).TASK_NAME);
            }

        }

    }

这就是它在这一刻的表现。

Answer 1

您需要使showTASK_LIST()静态。然后，您可以使用Task.showTASK_LIST();

进行调用

如下所示

   public static void showTASK_LIST(){
        for(int i = 0; i <= TASK_LIST.size(); i++){
            System.out.println(TASK_LIST.get(i).TASK_NAME);
        }

Task.showTASK_LIST();//goes in your main method to show the tasks

我运行代码时得到的结果在上面的代码中产生了一个indexOutOfBounds异常。这是一个简单的解决方案。

将您的for循环更改为此

for(int i = 0; i < TASK_LIST.size(); i++)// changed <= to <

只有3个任务，＆lt; =上升到导致问题的第四个任务

我得到了这个输出

Task 1 starts.
Task 3 starts.
Task 3 1
Task 1
Task 2
Task 3
Task 2 starts.
Task 1 1
Task 2 1
Task 3 2
Task 1 2
Task 2 2
Task 3 3
===========================================
Task 1 has been completed. Final result = 2
===========================================
Task 2 3
3
Task 3 4
Task 2 4
Task 2 5
Task 3 5
Task 2 6
===========================================
Task 3 has been completed. Final result = 5
===========================================
3
Task 2 7
Task 2 8
Task 2 9
Task 2 10
Task 2 11
Task 2 12
Task 2 13
Task 2 14
Task 2 15
Task 2 16
Task 2 17
Task 2 18
Task 2 19
Task 2 20
===========================================
Task 2 has been completed. Final result = 20
===========================================
3

Answer 2

您的代码存在线程安全问题，因为您尝试从多个线程读取/写入共享资源（在本例中为Task对象）上的值：

您正在从一个线程更改任务状态（写入）并尝试从不同的线程（读取）读取它，这是主线程就是这种情况：

Task.showTASK_LIST()

同样的问题还有：

      //Method to check current result
    public int getTASK_RESULT() {
        return TASK_RESULT;
    }

    //Method to check current status
    public String getTASK_STATUS() {
        return TASK_STATUS;
    }

您可以在以下位置阅读有关Java并发和线程安全的信息： https://en.wikipedia.org/wiki/Thread_safety https://docs.oracle.com/javase/tutorial/essential/concurrency/

我将在重复使用代码的同时提供我自己的实现，但在此之前，在您查看代码之前几个主题演讲：

使用Callable接口而不是Runnable，因为您希望在处理结束时返回结果（Callable类似于Runnable，但您可以返回结果
使用Executor submit（）方法返回Future对象（Future有许多有用的方法，如：isDone（），cancel（），get（）等...）
管理主线程中和Task类外的任务列表

StatusChangeListener

public interface StatusChangeListener {

  void statusChanged(String oldStatus, String newStatus);
}

主要

import java.util.ArrayList; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; public class Main { public static void main(String[] args) { ExecutorService executor = Executors.newCachedThreadPool(); //manage your tasks list here ArrayList<Task> tasks = new ArrayList<>(); Task t1 = new Task("Task 1", 2); Task t2 = new Task("Task 2", 20); Task t3 = new Task("Task 3", 5); tasks.add(t1); tasks.add(t2); tasks.add(t3); //add status change listener to be notified for t1 status changes t1.addStatusChangeListener(new MyListener()); System.out.println("tasks = " + tasks); //use submit instead of execute Future<Integer> future1 = executor.submit(t1); System.out.println("task 1 is done = " + future1.isDone()); Future<Integer> future2 = executor.submit(t2); Future<Integer> future3 = executor.submit(t3); //cancel task 3 future3.cancel(true); try { System.out.println("future 1 result= " + future1.get()); System.out.println("future 2 result= " + future2.get()); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } //you can do the same with the progress. e.g. add progress listener private static class MyListener implements StatusChangeListener{ @Override public void statusChanged(String oldStatus, String newStatus) { System.out.println(String.format("Thread : %s status changed from %s to %s", Thread.currentThread(), oldStatus, newStatus)); } } }

<强>任务

import java.util.concurrent.Callable; class Task implements Callable<Integer> { //can be replaced by enum private String TASK_STATUS; private String TASK_NAME; private int TASK_RESULT; private int TASK_GOAL; private StatusChangeListener statusChangeListener; public Task(String name, int goal) { this.TASK_NAME = name; this.TASK_GOAL = goal; this.TASK_STATUS = "INACTIVE"; } //private Method to change result private void setTASK_STATUS(String newStatus) { String oldStatus = TASK_STATUS; TASK_STATUS = newStatus; //notify status changes if (statusChangeListener != null) statusChangeListener.statusChanged(oldStatus, newStatus); } @Override public Integer call() throws Exception { setTASK_STATUS("ACTIVE"); System.out.println(TASK_NAME + " starts."); while (TASK_RESULT != TASK_GOAL) { //if (Thread.currentThread().isInterrupted()) return; TASK_RESULT++; System.out.println(TASK_NAME + " " + TASK_RESULT); try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } Thread.yield(); } System.out.println("===========================================\n" + TASK_NAME + " has been completed. Final result = " + TASK_GOAL + "\n==========================================="); setTASK_STATUS("COMPLETED"); return TASK_RESULT; } public void addStatusChangeListener(StatusChangeListener statusChangeListener) { this.statusChangeListener = statusChangeListener; } }

同时工作的任务

2 个答案: