[Java知识库]线程的状态与生命周期

1. 代码示例

package com.example.springbootthreaddemo.demo02;
import com.mysql.cj.util.TimeUtil;
import java.util.concurrent.TimeUnit;

public class Demo {
    public static void main(String[] args) {
        new Thread(()->{
            while(true){
                try {
                    TimeUnit.SECONDS.sleep(120);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"STATUS_01").start();  //阻塞状态

        new Thread(()->{
            while(true){
                synchronized (Demo.class){
                    try {
                        Demo.class.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        },"STATUS_02").start(); //阻塞状态

        new Thread(new BlockedDemo(),"BLOCKED-DEMO-01").start();
        new Thread(new BlockedDemo(),"BLOCKED-DEMO-02").start();

    }
    static class BlockedDemo extends  Thread{
        @Override
        public void run() {
            synchronized (BlockedDemo.class){
                while(true){
                    try {
                        TimeUnit.SECONDS.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

启动运行，然后在idea中的target目录下找到Demo.class ，右键 open in terminal, 执行jps查看Java进程pid,

对5444这个pid 执行jstack命令就可以看到Java进程的状态了

spring-boot-thread-demo\target\classes\com\example\springbootthreaddemo\demo0
2>jps
13168
11652 Jps
2532 Launcher
5444 Demo
13096

spring-boot-thread-demo\target\classes\com\example\springbootthreaddemo\demo0
2>jstack 5444
2021-11-21 22:22:19
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.181-b13 mixed mode):

"DestroyJavaVM" #18 prio=5 os_prio=0 tid=0x00000000016ec800 nid=0x2738 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"BLOCKED-DEMO-02" #17 prio=5 os_prio=0 tid=0x000000001bb84000 nid=0x1e0 waiting for monitor entry [0x000000001c6bf000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.example.springbootthreaddemo.demo02.Demo$BlockedDemo.run(Demo.java:46)
        - waiting to lock <0x00000000d6721898> (a java.lang.Class for com.example.springbootthreaddemo.demo02.Demo$BlockedDemo)
        at java.lang.Thread.run(Thread.java:748)

"BLOCKED-DEMO-01" #15 prio=5 os_prio=0 tid=0x000000001bb83000 nid=0x4064 waiting on condition [0x000000001c5be000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at java.lang.Thread.sleep(Thread.java:340)
        at java.util.concurrent.TimeUnit.sleep(TimeUnit.java:386)
        at com.example.springbootthreaddemo.demo02.Demo$BlockedDemo.run(Demo.java:46)
        - locked <0x00000000d6721898> (a java.lang.Class for com.example.springbootthreaddemo.demo02.Demo$BlockedDemo)
        at java.lang.Thread.run(Thread.java:748)

"STATUS_02" #13 prio=5 os_prio=0 tid=0x000000001bb70800 nid=0x4018 in Object.wait() [0x000000001c4bf000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000d63f8ef0> (a java.lang.Class for com.example.springbootthreaddemo.demo02.Demo)
        at java.lang.Object.wait(Object.java:502)
        at com.example.springbootthreaddemo.demo02.Demo.lambda$main$1(Demo.java:28)
        - locked <0x00000000d63f8ef0> (a java.lang.Class for com.example.springbootthreaddemo.demo02.Demo)
        at com.example.springbootthreaddemo.demo02.Demo$$Lambda$2/443308702.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:748)

"STATUS_01" #12 prio=5 os_prio=0 tid=0x000000001bb6c800 nid=0x34c0 waiting on condition [0x000000001c3bf000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at java.lang.Thread.sleep(Thread.java:340)
        at java.util.concurrent.TimeUnit.sleep(TimeUnit.java:386)
        at com.example.springbootthreaddemo.demo02.Demo.lambda$main$0(Demo.java:17)
        at com.example.springbootthreaddemo.demo02.Demo$$Lambda$1/205797316.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:748)

上面的状态可以看到：
STATUS_01 线程的状态是TIMED_WAITING， 这是因为调用sleep是设置了超时时间
STATUS_02 线程的状态是WAITING， 调用wait方法时没有设置超时时间
BLOCKED-DEMO-01线程的状态是TIMED_WAITING ，该线程先抢到了锁，执行带超时时间的sleep方法，因此线程状态是TIMED_WAITING,
BLOCKED-DEMO-02线程的状态是BLOCKED 由于BLOCKED-DEMO-01抢到了锁并且在sleep过程中，BLOCKED-DEMO-02线程处于锁等待状态中，因此它的线程状态是 BLOCKED. 上面几种线程状态都属于阻塞，但是区别如下：

调用带超时时间的wait sleep join LockSupport.park 方法时，线程状态是TIMED_WAITING
调用不带超时时间的wait sleep join LockSupport.park 方法时，线程状态是WAITING，
当线程获取锁失败，处于锁等待时，当前线程状态是BLOCKED

线程生命周期：5种线程状态 or 7种线程状态？
站在Java的角度来说，一共有七种线程状态，而对于操作系统层面来说，它没有新建和种植状态，只有就绪，运行，waiting ，timed_waiting, 阻塞五种状态。

线程启动做了哪些事情 thread.start() or thread.run() ?
java是不能够创建线程的，Java创建线程本质上是调用了一个本地方法 start0(), 通过jvm 最终由OS创建出线程，当线程通过CPU的调度算法获取到CPU资源时，就可以真正的执行了。