Java多线程同步问题：死锁处理实例

原创小灰灰 2024-09-20 01:12 66阅读 0赞

死锁是多线程编程中常见的问题，当两个或更多的线程相互等待对方释放资源时，就会出现死锁。

以下是一个简单的Java死锁处理实例：

```java
// 假设我们有四个共享资源（resource）：
class Resource {
    int id;
    Lock lock; // 锁对象

Resource(int id) {
        this.id = id;
        lock = new Lock(id);
    }

void acquire() {
        lock.lock();
    }

void release() {
        lock.unlock();
    }
}

// 锁类
class Lock {
    int id;

Lock(int id) {
        this.id = id;
    }

// 获取锁
    boolean tryLock(Resource resource) {
        if (resource.id == id) {
            resource.acquire();
            return true; // 获取了锁
        } else {
            return false; // 无法获取其他线程的锁，返回false
        }
    }

// 释放锁
    void unlock(Resource resource) {
        if (resource.id == id) {
            resource.release();
        }
    }
}

// 多线程示例
class DeadLockExample {
    private Resource r1, r2, r3, r4;

public DeadLockExample() {
        // 创建所有资源，这里假设每个资源都需要两个锁（r1和r2，r3和r4）
        r1 = new Resource(1);
        r2 = new Resource(2);
        r3 = new Resource(3);
        r4 = new Resource(4);

// 为每个资源创建一个线程
        Thread t1 = new Thread(() -> acquireResource(r1, r2))));
        Thread t2 = new Thread(() -> acquireResource(r3, r4))));
        Thread t3 = new Thread(() -> releaseResource(t1, r1), r2)));
        Thread t4 = new Thread(() -> releaseResource(t2, r3), r4)));

// 启动所有线程
        t1.start();
        t2.start();
        t3.start();
        t4.start();
    }

private void acquireResource(Resource r1, Resource r2)) {
        if (r1.tryLock(r2)) {
            System.out.println("Thread 1 acquired resource 1 and 2");
        } else {
            System.out.println("Thread 1 failed to acquire resource 1 and 2");
        }
    }

private void releaseResource(Thread owner, Resource r1, Resource r2) {
        if (owner.equals(Thread.currentThread()))) {
            if (r1.unlock(r2)) {
                System.out.println("Thread " + Thread.currentThread().getName() + " released resource 1 and 2");
            } else {
                System.out.println("Thread " + Thread.currentThread().getName() + " failed to release resource 1 and 2");
            }
        } else {
            System.out.println("Thread " + Thread.currentThread().getName() + " attempted to release a resource owned by another thread (owner = " + owner.getName() + ")");
        }
    }
}
```

在这个例子中，我们创建了四个共享资源（r1、r2、r3和r4），每个资源都需要两个锁。然后我们为每个资源创建了一个线程，线程会尝试获取并释放资源。

如果所有线程的执行顺序正确，并且每个线程在获取和释放资源时都遵守了锁的规则，那么就不会出现死锁。