一个简单的java多线程

Question

好吧,我遇到了一个惊人的问题......

public class Test {
    private boolean[] state = new boolean[]{false, false};

    public void createThread() {
        Thread th1  = new Thread(() -> {
            try {
                System.out.println("1");
                Thread.sleep(2000);
                state[0]=true;
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        Thread th2 = new Thread(() -> {
            try {
                System.out.println("2");
                Thread.sleep(2000);
                state[1] = true;
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        });
        th1.start();
        th2.start();
    }
    public static void main(String args[]) throws InterruptedException {
        Test test = new Test();
        test.createThread();
        while (true) {
//            Thread.sleep(1);
            if (test.state[0] && test.state[1]) {
                System.out.println("stopped");
                break;
            }
        }
    }
}

如果我不添加Thread.sleep(1)语句或其他代码,则"停止"不会被打印.如果我添加内容while,将打印"停止".这会怎么样？每个答案都有帮助.

Answer 1

答案可能很简单,但在于细节.

你的阵列,它保持状态没有被标记为volatile,因此if-statement在你的while循环不会被迫使用最新值.

简单地改变

private boolean[] state = new boolean[] { false, false };

至

private volatile boolean[] state = new boolean[] { false, false };

会诀窍.