线程状态

Thread.state

New	尚未启动的线程处于此状态
Runnable	在java虚拟机中执行的线程处于此状态
Blocked	被阻塞等待监视器锁定的线程处于此状态
Waiting	正在等待另一个线程执行特定动作的线程处于此状态
Time_Waiting	正在等待另一个线程执行动作达到指定等待时间的线程处于此状态
Terminated	已退出的线程处于此状态

package Thread;

/**
 * @author zxy
 * 观察测试线程的状态
 *
 */
public class TestState {

	public static void main(String[] args) throws InterruptedException {
		Thread thread = new Thread(()->{
			for(int i = 0; i < 5; i++) {
				try {
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
			System.out.println("");
		});
		
		/* 观察状态 */
		Thread.State state = thread.getState();
		System.out.println(state);
		
		/* 观察启动后 */
		thread.start();//启动线程
		state = thread.getState();
		System.out.println(state);//run
		
		/* 只要线程不终止，就一直输出状态 */
		while(state != Thread.State.TERMINATED) {
			Thread.sleep(100);
			/* 更新线程状态 */
			state = thread.getState();
			System.out.println(state);
		}
		
	}
}

输出：

NEW
RUNNABLE
TIMED_WAITING
TIMED_WAITING

·········

TIMED_WAITING

TERMINATED

---

线程优先级

• java提供一个线程调度器来监控程序中启动后进入就绪状态的所有线程，线程调度器按照优先级决定应该调度哪个线程来执行
• 线程的优先级用数字表示，范围从1-10
  • Thread.MIN_PRIORITY = 1;
  • Thread.MAX_PRIORITY = 10;
  • Thread.NORM_PRIORITY = 5;
• 使用以下方式改变或获取优先级：
  • getPriority().setPriority(int xxx)
• 优先级的设定建议在start调度前
• 优先级低只是意味着获得调度的概率低，并不是优先级低就不会被调用了，这都是看CPU的调度

package Thread;

public class TestPriority {

	public static void main(String[] args) {
		/* 主线程默认优先级 */
		System.out.println(Thread.currentThread().getName()+
				"-->"+Thread.currentThread().getPriority());
		
		MyPriority myPriority = new MyPriority();
		
		Thread t1 = new Thread(myPriority);
		Thread t2 = new Thread(myPriority);
		Thread t3 = new Thread(myPriority);
		Thread t4 = new Thread(myPriority);
		Thread t5 = new Thread(myPriority);
		
		/* 先设置优先级 再启动start方法 */
		t1.start();
		
		t2.setPriority(1);
		t2.start();
		
		t3.setPriority(Thread.MAX_PRIORITY);
		t3.start();
		
		t4.setPriority(8);
		t4.start();
		
		t5.setPriority(Thread.MAX_PRIORITY);
		t5.start();
		
	}
	
}

class MyPriority implements Runnable{

	@Override
	public void run() {
		// TODO Auto-generated method stub
		System.out.println(Thread.currentThread().getName()+
				"-->"+Thread.currentThread().getPriority());
	}
	
}

---

守护线程

• 线程分为用户线程和守护线程
• 虚拟机必须确保用户线程执行完毕
• 虚拟机不用等待守护线程执行完毕
• 如 后台记录操作日志、监控内存、垃圾回收等待