Java多线程并发问题：死锁案例

原创以你之姓@ 2024-10-15 08:18 57阅读 0赞

死锁是多线程编程中的一种严重问题，它会导致所有线程都无法继续执行。

以下是一个经典的Java死锁案例：

```java
// 线程1，拥有资源A和B
class ResourceA {
    int count = 1;
    synchronized void use() {
        count--;
        System.out.println("Resource A used by Thread-1");
        if (count == 0) {
            System.out.println("Resource A released by Thread-1");
        }
    }
}

class ResourceB {
    int count = 1;
    synchronized void use() {
        count--;
        System.out.println("Resource B used by Thread-1");
        if (count == 0) {
            System.out.println("Resource B released by Thread-1");
        }
    }
}

// 线程2，拥有资源C和D
class ResourceC {
    int count = 1;
    synchronized void use() {
        count--;
        System.out.println("Resource C used by Thread-2");
        if (count == 0) {
            System.out.println("Resource C released by Thread-2");
        }
    }
}

class ResourceD {
    int count = 1;
    synchronized void use() {
        count--;
        System.out.println("Resource D used by Thread-2");
        if (count == 0) {
            System.out.println("Resource D released by Thread-2");
        }
    }
}

public class DeadlockExample {
    private ResourceA ra1 = new ResourceA();
    private ResourceB rb1 = new ResourceB();
    private ResourceC rc1 = new ResourceC();
    private ResourceD rd1 = new ResourceD();

public void startThreads() {
        // 线程1，获取资源A和B
        Thread thread1 = new Thread(() -> ra1.use() && rb1.use()));
        thread1.start();

// 线程2，获取资源C和D
        Thread thread2 = new Thread(() -> rc1.use() && rd1.use()));
        thread2.start();
    }

public static void main(String[] args) {
        DeadlockExample example = new DeadlockExample();
        example.startThreads();
    }
}
```

这个例子中，线程1拥有资源A和B（`ra1.use()` 和 `rb1.use()`），线程2拥有资源C和D（`rc1.use()` 和 `rd1.use()`）。

当线程1先使用完A后，会释放资源A，然后尝试去获取资源B。此时，如果线程2已经使用完C后释放了资源C，但是资源D还没被线程2使用完毕，那么线程1就无法获取到资源B，从而形成死锁。