性能瓶颈：Java多线程通信中的死锁问题示例。

原创小咪咪 2024-11-15 17:48 9阅读 0赞

在Java多线程通信中，死锁问题通常发生在两个或更多的线程互相等待对方释放资源时。

以下是一个简单的死锁问题示例：

```java
// 线程1需要资源A和资源B
class Thread1 extends Thread {
    private ResourceA ra;
    private ResourceB rb;

Thread1(ResourceA ra, ResourceB rb) {
        this.ra = ra;
        this.rb = rb;
    }

@Override
    public void run() {
        ra.acquire();
        rb.acquire();

System.out.println("Thread 1 acquired both resources");
        ra.release();
        rb.release();

System.out.println("Thread 1 released both resources back to pool");
    }
}

// 线程2需要资源B和资源C
class Thread2 extends Thread {
    private ResourceB rb;
    private ResourceC rc;

Thread2(ResourceB rb, ResourceC rc) {
        this.rb = rb;
        this.rc = rc;
    }

@Override
    public void run() {
        rb.acquire();
        rc.acquire();

System.out.println("Thread 2 acquired both resources");
        rb.release();
        rc.release();

System.out.println("Thread 2 released both resources back to pool");
    }
}

// 资源类
class Resource {
    private boolean isAcquired;

public Resource() {
        this.isAcquired = false;
    }

// 设置资源是否被获取
    public void setAcquired(boolean isAcquired) {
        this.isAcquired = isAcquired;
    }

// 检查资源是否被获取
    public boolean isAcquired() {
        return this.isAcquired;
    }
}

// 主程序
public class Main {
    private ResourceA ra;
    private ResourceB rb;
    private ResourceC rc;

public Main(ResourceA ra, ResourceB rb, ResourceC rc) {
        this.ra = ra;
        this.rb = rb;
        this.rc = rc;
    }

public static void main(String[] args) {
        // 创建资源
        ResourceA ra = new ResourceA();
        ResourceB rb = new ResourceB();
        ResourceC rc = new ResourceC();

// 创建线程并启动
        Main main = new Main(ra, rb, rc);
        Thread thread1 = new Thread(main::runThread1));
        Thread thread2 = new Thread(main::runThread2));
        thread1.start();
        thread2.start();
    }

// 线程1执行方法
    private void runThread1() {
        while (!ra.isAcquired() || !rb.isAcquired())) {
            // 线程1尝试获取资源A和资源B
            ra.acquire();
            rb.acquire();

System.out.println("Thread 1 acquired both resources");

try {
                // 等待资源释放回线程池
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

// 如果成功获取资源，释放资源并打印信息
            if (ra.isAcquired() && rb.isAcquired())) {
                ra.release();
                rb.release();

System.out.println("Thread 1 released both resources back to pool");

break;
            }
        }
    }

// 线程2执行方法
    private void runThread2() {
        while (!rc.isAcquired() || !rb.isAcquired())) {
            // 线程2尝试获取资源C和资源B
            rc.acquire();
            rb.acquire();

System.out.println("Thread 2 acquired both resources");

try {
                // 等待资源释放回线程池
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

// 如果成功获取资源，释放资源并打印信息
            if (rc.isAcquired() && rb.isAcquired())) {
                rc.release();
                rb.release();

System.out.println("Thread 2 released both resources back to pool");

break;
            }
        }
    }
}
```

在这个示例中，两个线程分别需要资源A、B和C。然而，它们获取资源的方式是相互依赖的：线程1先获取资源A和B，然后线程2再尝试获取资源C和资源B。这种顺序导致了死锁问题。

要解决这个问题，可以修改资源或线程的获取策略，确保不会出现循环等待的情况。例如，可以让线程先获取资源B，然后在需要资源A时再获取。这样可以避免死锁的发生。