Thread 的join的实现中有点迷惑的地方

最新推荐文章于 2024-08-18 16:24:19 发布

原创最新推荐文章于 2024-08-18 16:24:19 发布 · 114 阅读

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文章标签：

#thread #Socket #活动 #IDEA

本文通过一个具体的Java程序示例，详细探讨了线程的生命周期、线程间的状态及交互方式，并展示了如何使用Thread类的方法join来同步线程执行。

	
	package test;	

	/**	
	 * Created by IntelliJ IDEA.	
	 * Date: 11/06/28
	 * Time: 10:26
	 */
	public class IsThreadPool {
	    public static void main(String[] args) {
	        System.out.println("begin >>> " + Thread.currentThread().getName() + "  isAlive: " + Thread.currentThread().isAlive());
	        ChildThread child1 = new ChildThread();
	        child1.start();
	        try {
	            child1.joinExtend(0);
	//            child1.join(0);
	        } catch (InterruptedException e) {
	            e.printStackTrace();
	        }
	        System.out.println("end >>> " + Thread.currentThread().getName() + "  isAlive: " + Thread.currentThread().isAlive());
	    }

	}

	class ChildThread extends Thread {
	    public void run() {
	        int i = 4;
	        while (--i >= 0) {
	            try {
	                Thread.sleep(2000);
	            } catch (InterruptedException e) {
	                e.printStackTrace();
	            }
	            System.out.println("==============================================================");
	            System.out.println(Thread.currentThread().getName() + "  isAlive: " + Thread.currentThread().isAlive());
	            ThreadGroup tg = Thread.currentThread().getThreadGroup();
	            System.out.println(tg.toString());
	            Thread[] threads = new Thread[tg.activeCount()];
	            tg.enumerate(threads);
	            for (Thread t : threads) {
	                System.out.println("    ThreadGroup_child: " + t.getName() + "   state: " + t.getState());
	            }
	            tg = null;

	        }


	    }

	    /**
	     * 对Thread的join作修改，看看变量情况，
	     * isAlive（）：测试线程(并不是当前线程）是否处于活动状态。如果线程已经启动且尚未终止，则为活动状态。
	     * wait:在其他线程调用此对象的 notify() 方法或 notifyAll() 方法，或者超过指定的时间量前，导致当前线程等待
	     * @param millis
	     * @throws InterruptedException
	     */
	    public final synchronized void joinExtend(long millis)
	            throws InterruptedException {

	        long base = System.currentTimeMillis();
	        long now = 0;
	        boolean isAlive = this.isAlive();
	        while (isAlive = this.isAlive()) {
	            System.out.println("joinExtend_currentThread--->  " + Thread.currentThread().getName());
	            System.out.println("this ---> " + this.getName() + "   alive---> " + isAlive + "  currentThread---> " + Thread.currentThread().getName());
	            this.wait(0);
	        }

	    }
	}

结果：

Connected to the target VM, address: '127.0.0.1:1759', transport: 'socket'
begin >>> main isAlive: true
joinExtend_currentThread---> main
this ---> Thread-0 alive---> true currentThread---> main
==============================================================
Thread-0 isAlive: true
java.lang.ThreadGroup[name=main,maxpri=10]
ThreadGroup_child: main state: WAITING
ThreadGroup_child: Thread-0 state: RUNNABLE
==============================================================
Thread-0 isAlive: true
java.lang.ThreadGroup[name=main,maxpri=10]
ThreadGroup_child: main state: WAITING
ThreadGroup_child: Thread-0 state: RUNNABLE
==============================================================
Thread-0 isAlive: true
java.lang.ThreadGroup[name=main,maxpri=10]
ThreadGroup_child: main state: WAITING
ThreadGroup_child: Thread-0 state: RUNNABLE
==============================================================
Thread-0 isAlive: true
java.lang.ThreadGroup[name=main,maxpri=10]
ThreadGroup_child: main state: WAITING
ThreadGroup_child: Thread-0 state: RUNNABLE
end >>> main isAlive: true
Disconnected from the target VM, address: '127.0.0.1:1759', transport: 'socket'

Process finished with exit code 0