深入探究Java线程不安全的原因与解决

static class Counter {
    public int count = 0;
    void increase() {
        count++;
    }
}
    public static void main(String[] args) throws InterruptedException {
        final Counter counter = new Counter();
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                counter.increase();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                counter.increase();
            }
        });
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(counter.count);
}

   private static int count = 0;
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            while (count == 0) {
            }
            System.out.println(Thread.currentThread().getName() +
                    "执⾏完成");
        });
        t1.start();
        Scanner scanner = new Scanner(System.in);
        System.out.print("->");
        count = scanner.nextInt();
    }

/**
 * 内存可见性
 * 线程1没感受到flag的变化，实际线程2已经改变了flag的值
 * 使用volatile，解决内存可见性和指令重排序
 */
public class ThreadSeeVolatile {
    //全局变量
    private volatile static boolean flag = true;
    public static void main(String[] args) {
        //创建子线程
        Thread t1 = new Thread(() ->{
            System.out.println("1开始执行：" + LocalDateTime.now());
            while(flag){
            }
            System.out.println("2结束执行" + LocalDateTime.now());
        });
        t1.start();
        Thread t2 = new Thread(() ->{
            //休眠1s
            try {
                Thread.sleep(10000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("修改flag=false"+ LocalDateTime.now());
            flag = false;
        });
        t2.start();
    }
}

   // 修饰一个代码块： 明确指定锁哪个对象
    public void test1(int j) {
        synchronized (this) {
        }
    }
    // 修饰一个方法
    public synchronized void test2(int j) {
    }
    // 修饰一个类
    public static void test1(int j) {
        synchronized (SynchronizedExample2.class) {
        }
    }
    // 修饰一个静态方法
    public static synchronized void test2(int j) {
    }