java实现死锁

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public class DeadLockDemo {

    private static Object resource1 = new Object();
    private static Object resource2 = new Object();

    public static void main(String[] args) {
        new Thread(() -> {
            synchronized (resource1) {

                System.out.println(Thread.currentThread() + "get resource1");

                try {
                    // 线程休眠，保证线程2先获得资源2
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println(Thread.currentThread() + "waiting get resource2");

                synchronized (resource2) {
                    System.out.println(Thread.currentThread() + "get resource2");
                }
            }
        }, "T1").start();

        new Thread(() -> {
            synchronized (resource2) {

                System.out.println(Thread.currentThread() + "get resource2");

                try {
                    // 线程休眠，保证线程1先获得资源1
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println(Thread.currentThread() + "waiting get resource1");

                synchronized (resource1) {
                    System.out.println(Thread.currentThread() + "get resource1");
                }
            }
        }, "T2").start();

    }
}

程序结果

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Thread[T1,5,main]get resource1
Thread[T2,5,main]get resource2
Thread[T1,5,main]waiting get resource2
Thread[T2,5,main]waiting get resource1

死锁原因

T1和T2各自同时占有resource1和resource2，而又分别要使用resource2和resource1，因此发生死锁。

解决方法

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public class DeadLockDemo {

    private static Object resource1 = new Object();
    private static Object resource2 = new Object();

    public static void main(String[] args) {
        new Thread(() -> {
            synchronized (resource1) {

                System.out.println(Thread.currentThread() + "get resource1");

                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println(Thread.currentThread() + "waiting get resource2");

                synchronized (resource2) {
                    System.out.println(Thread.currentThread() + "get resource2");
                }
            }
        }, "T1").start();

        new Thread(() -> {
            synchronized (resource1) {

                System.out.println(Thread.currentThread() + "get resource2");

                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println(Thread.currentThread() + "waiting get resource1");

                synchronized (resource2) {
                    System.out.println(Thread.currentThread() + "get resource1");
                }
            }
        }, "T2").start();

    }
}

程序结果

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Thread[T1,5,main]get resource1
Thread[T1,5,main]waiting get resource2
Thread[T1,5,main]get resource2
Thread[T2,5,main]get resource2
Thread[T2,5,main]waiting get resource1
Thread[T2,5,main]get resource1

分析

可以让两个线程按照顺序依次使用resource1和resource2