Java并发编程中锁升级和死锁的实例展示

原创谁借莪１个温暖的怀抱￠ 2024-09-16 06:04 10阅读 0赞

在Java并发编程中，锁升级和死锁是两个重要的概念。下面我将通过具体的实例来解释这两者。

1. 锁升级：
   简单来说，锁升级就是从低级锁升级到高级锁的过程。这通常发生在多线程环境下，当一个线程获取某个对象的低级锁后，如果尝试获取该对象的高级锁（如synchronized(this)），那么就需要将当前的低级锁升级为高级锁。

实例：
```java
class LockUpgradeExample {
    private Object lockObject = new Object();

public void method1() {
        synchronized (lockObject) { // low-level lock
            if (conditionForUpgrade()) { // upgrade condition
                synchronized (lockObject) asLockUpgrade(); // upgrading to high-level lock
            }
        }
    }

private boolean conditionForUpgrade() {
        // your upgrade condition, like a resource is available
        return true;
    }

private void asLockUpgrade() {
        // your code inside the high-level lock block
        System.out.println("Inside high-level lock");
    }
}
```
2. 死锁：
   死锁是指两个或多个并发进程在执行过程中，因争夺资源而造成的一种相互等待的现象，若无外力干涉，它们都将无法继续执行下去。

实例：
```java
class DeadlockExample {
    private Object lockObject1 = new Object();
    private Object lockObject2 = new Object();

public void method2() {
        synchronized (lockObject1) { // lock 1
            if (conditionForLockedLock1()) { // locked condition
                try {
                    // lock 2, but it's already locked by lock 1
                    synchronized (lockObject2) asAlreadyLocked(); // deadlock
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

private boolean conditionForLockedLock1() {
        // your locked condition for lock 1, like a resource is in use
        return true;
    }

private void asAlreadyLocked() throws InterruptedException {
        System.out.println("Lock 2 is already locked by Lock 1");
        Thread.sleep(500); // simulate a long wait before recovery action
    }
}
```
在这个例子中，`method2()`试图获取`lockObject2`的锁，但此时`lockObject2`已被`method1()`获得了锁。这就形成了一个死锁状态。