Java线程的几种状态-优快云博客

一. 线程状态一共有几种

观察线程的所有状态

线程的状态是⼀个枚举类型 Thread.State

public class ThreadState {
 public static void main(String[] args) {
 for (Thread.State state : Thread.State.values()) {
 System.out.println(state);
 }
 }
}

• NEW: 安排了⼯作, 还未开始⾏动

• RUNNABLE: 可⼯作的. ⼜可以分成正在⼯作中和即将开始⼯作.

• BLOCKED: 这⼏个都表⽰排队等着其他事情

• WAITING: 这⼏个都表⽰排队等着其他事情

• TIMED_WAITING: 这⼏个都表⽰排队等着其他事情

• TERMINATED: ⼯作完成了.

观察线程的状态和转移

使⽤ jconsole 命令观察线程

关注 NEW 、 RUNNABLE 、 TERMINATED 状态的转换

public class ThreadStateTransfer {
 public static void main(String[] args) throws InterruptedException {
 Thread t = new Thread(() -> {
 for (int i = 0; i < 1000_0000; i++) {
}
 }, "李四");
 System.out.println(t.getName() + ": " + t.getState());;
 t.start();
 while (t.isAlive()) {
 System.out.println(t.getName() + ": " + t.getState());;
 }
 System.out.println(t.getName() + ": " + t.getState());;
 }
}

关注 WAITING 、 BLOCKED 、 TIMED_WAITING 状态的转换

public static void main(String[] args) {
 final Object object = new Object();
 Thread t1 = new Thread(new Runnable() {
 @Override
 public void run() {
 synchronized (object) {
 while (true) {
 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }
 }
 }
 }, "t1");
 t1.start();
 Thread t2 = new Thread(new Runnable() {
 @Override
 public void run() {
 synchronized (object) {
 System.out.println("hehe");
 }
 }
 }, "t2");
 t2.start();
}

使⽤ jconsole 可以看到 t1 的状态是 TIMED_WAITING , t2 的状态是 BLOCKED

修改上⾯的代码, 把 t1 中的 sleep 换成 wait

public static void main(String[] args) {
 final Object object = new Object();
 Thread t1 = new Thread(new Runnable() {
 @Override
 public void run() {
 synchronized (object) {
 try {
 // [修改这⾥就可以了!!!!!]
 // Thread.sleep(1000);
 object.wait();
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }
 }
 }, "t1");
 ...
}

使⽤ jconsole 可以看到 t1 的状态是 WAITING

结论:

• BLOCKED 表⽰等待获取锁, WAITING 和 TIMED_WAITING 表⽰等待其他线程发来通知.

• TIMED_WAITING 线程在等待唤醒，但设置了时限; WAITING 线程在⽆限等待唤醒