多线程面试题：子线程循环10次，接着主线程循环100次；接着回到子线程循环10次，然后再回到主线程循环100次，如此交替50次。

最新推荐文章于 2024-07-11 15:18:28 发布

superKKOne

最新推荐文章于 2024-07-11 15:18:28 发布

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分类专栏： java 文章标签：多线程面试题

本文链接：https://blog.youkuaiyun.com/book_karlzhouzhi/article/details/39107513

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本文探讨了并发编程中的线程同步机制，通过实例展示了使用wait和notify方法实现线程间的协调与通信，强调了在wait方法中使用while循环的重要性以避免假唤醒等问题。

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public static void main(String[] args){
	final Business b = new Business();
	new Thread(){
		@Override
		public void run(){
			for(int i=1; i<=50; i++){
				b.sub(i);
			}
		}
	}.start();
	
	
	for(int i=1; i<=50; i++){
		b.main(i);
	}
}
class Business{
	private boolean bShouldSub = true;
	public synchronized void main(int i){
		while(bShouldSub){
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		for(int j=1; j<=100; j++){
			System.out.println(Thread.currentThread().getName() + ", loop times: " + j + " of " + i);
		}
		bShouldSub = true;
		this.notify();
	}
	public synchronized void sub(int i){
		while(!bShouldSub){
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		for(int j=1; j<=10; j++){
			System.out.println(Thread.currentThread().getName() + ", loop times: " + j + " of " + i);
		}
		bShouldSub = false;
		this.notify();
	}
}

注意：在wait一定放在while循环里，不要用if来判断条件，防止假唤醒（比如interrupt或者timeout），参见wait方法的jdk描述：

A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one:
```
     synchronized (obj) {
         while (<condition does not hold>)
             obj.wait(timeout);
         ... // Perform action appropriate to condition
     }
 
```
(For more information on this topic, see Section 3.2.3 in Doug Lea's "Concurrent Programming in Java (Second Edition)" (Addison-Wesley, 2000), or Item 50 in Joshua Bloch's "Effective Java Programming Language Guide" (Addison-Wesley, 2001).