java - 如何在 Runnable 上设置参数然后获取值？

Question

我想在 Runnable 上设置参数然后获取值。

我写了这段代码。当我运行此代码时，返回 [2, 3, 3]。因为线程共享temp_value。

然后我添加了 sleep ，但它被注释掉了。结果是[1, 2, 3]。它工作正常!但是..它不是真正的多线程，对吧？

即使它正在运行多线程，但我需要等待每个进程完成共享值。

如何解决这个问题？

import java.util.ArrayList;

public class Foo implements Runnable {
    private int temp_value;
    private ArrayList<Integer> values = new ArrayList<Integer>();
    private ArrayList<Integer> newValues = new ArrayList<Integer>();

    public Foo(ArrayList<Integer> values) {
        this.values = values;
    }

    public static void main(String[] args) {

//      make initial values
        ArrayList<Integer> values = new ArrayList<Integer>();
        values.add(1);
        values.add(2);
        values.add(3);

//      set values then process and get new values
        Foo foo = new Foo(values);
        foo.startAppendValue(foo);
        System.out.println(foo.getNewValues());

    }

    public void startAppendValue(Foo foo) {

        Thread thread = null;
        int max = values.size();
        for (int i = 0; i < max; i++) {
            foo.temp_value =foo.values.get(i);
            thread = new Thread(foo);
            thread.start();
//          try {
//              Thread.sleep(10);
//          } catch (Exception e) {
//              // TODO: handle exception
//          }
        }
        try {
            thread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }


    @Override
    public void run() {
        newValues.add(temp_value);
    }

    public ArrayList<Integer> getNewValues() {
        return this.newValues;
    }
}

Answer 1

您可以使用 Callable 和 ExecutorService 来做这些事情

public class MyCallable implements Callable<Integer> { //Callable is like Runnable but can return value
  private Integer value;

  public MyCallable(Integer v) {
    value = v;
  }

  public Integer call() {
    return value;
  }

  public static void main(String[] args) {
    ExecutorService exec = Executors.newFixedThreadPool(3); //Creating thread pool with 3 worker threads
    List<Integer> values = Arrays.asList(1, 2, 3);
    List<Future<Integer>> futures = new ArrayList<>(values.size());
    List<Integer> newValues = new ArrayList<>(values.size());

    for (Integer v : values) {
        futures.add(exec.submit(new MyCallable(v))); //Submit tasks to worker threads to do stuff in background
    }

    for (Future<Integer> f : futures) {
        try {
            newValues.add(f.get()); // get calculated result from worker thread or block waiting for result to become available
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
    }

    System.out.println(newValues);
    exec.shutdownNow();
  }
}