Java多线程同步：Deadlock示例

原创痛定思痛。 2024-10-13 11:09 31阅读 0赞

在Java多线程编程中，死锁是一种常见的线程同步问题。以下是一个简单的Java Deadlock示例：

```java
// 创建两个互斥资源的类
class Resource1 {
    private boolean locked = false;

public synchronized void lock() {
        if (locked) {
            throw new IllegalStateException("Resource 1 is already locked");
        }
        locked = true;
        notifyAll(); // 唤醒等待锁的线程
    }

public synchronized void unlock() {
        if (!locked) {
            throw new IllegalStateException("Resource 1 is not locked");
        }
        locked = false;
        notifyAll(); // 唤醒等待解锁的线程
    }
}

class Resource2 {
    private boolean locked = false;

public synchronized void lock() {
        if (locked) {
            throw new IllegalStateException("Resource 2 is already locked");
        }
        locked = true;
        notifyAll(); // 唤醒等待锁的线程
    }

public synchronized void unlock() {
        if (!locked) {
            throw new IllegalStateException("Resource 2 is not locked");
        }
        locked = false;
        notifyAll(); // 唤醒等待解锁的线程
    }
}

// 创建两个线程，各自尝试获取资源并释放
public class DeadlockExample {
    public static void main(String[] args) {
        Resource1 resource1 = new Resource1();
        Resource2 resource2 = new Resource2();

Thread thread1 = new Thread(() -> {
            try {
                resource1.lock(); // 获取锁1
                resource2.lock(); // 获取锁2
                System.out.println("Thread 1 acquired both locks");
            } catch (InterruptedException | IllegalStateException e) {
                e.printStackTrace();
            } finally {
                resource1.unlock(); // 释放锁1
                resource2.unlock(); // 释放锁2
                System.out.println("Thread 1 released both locks");
            }
        }));

Thread thread2 = new Thread(() -> {
            try {
                resource1.lock(); // 获取锁1
                resource2.lock(); // 获取锁2
                System.out.println("Thread 2 also acquired both locks, causing deadlock!");
            } catch (InterruptedException | IllegalStateException e) {
                e.printStackTrace();
            } finally {
                resource1.unlock(); // 释放锁1
                resource2.unlock(); // 释放锁2
                System.out.println("Thread 2 released both locks");
            }
        }));

thread1.start();
        thread2.start();
    }
}
```

在这个例子中，两个线程分别尝试获取`Resource1`和`Resource2`的锁。如果线程A先获取到`resource1`的锁，然后线程B再获取到`resource2`的锁，此时就会形成死锁（Deadlock）。