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线程的状态一共有以下几种:
1)NEW 2)RUNNABLE 3)BLOCKED 4)WAITING 5)TIMED_WAITING 6)TERMINATED 我怎么知道的呢?来来,看一下源码: Thread.class里面:public static enum State { NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED; private State() { } }
1)New
当new了一个Thread,没有调用他的任何方法,他就处于New状态; 直接上代码:package com.test.main;public class Test { static class MyThread extends Thread{ public MyThread(String name){ super(name); } public void run(){ System.out.println("myThread打印线程名"+Thread.currentThread().getName()); } } public static void main(String[] args) { MyThread thread = new MyThread("myThread"); System.out.println("线程名:"+thread.getName()+",线程状态:"+thread.getState()); }}运行结果:线程名:myThread,线程状态:NEWProcess finished with exit code 0
2)RUNNABLE
当线程调用了start方法,线程如果处于等待操作系统分配CPU资源,等待IO连接,此时处于Ready状态 ,处于已经在运行,那就处于Running状态; 为什么这里有两种呢?因为调用了start,不一定能立马拿到cpu执行时间片,这时候是不太确定的。 我们加上thread.start:package com.test.main;public class Test { static class MyThread extends Thread{ public MyThread(String name){ super(name); } public void run(){ System.out.println("myThread打印线程名"+Thread.currentThread().getName()); } } public static void main(String[] args) { MyThread thread = new MyThread("myThread"); thread.start(); System.out.println("线程名:"+thread.getName()+",线程状态:"+thread.getState()); }}运行结果:线程名:myThread,线程状态:RUNNABLE
3)BLOCKED
当线程尝试拿锁,但是锁一直被占用,线程这时候会被操作系统挂起,这是被称为线程阻塞; 实例代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 Thread t1 = new Thread(new Runnable() { public void run() { synchronized(sdf){ while (true){ } } } }); t1.setName("线程1"); t1.start(); Thread.sleep(1000); //线程2 Thread t2 = new Thread(new Runnable() { public void run() { synchronized (sdf){ System.out.println("线程2拿锁打印当前日期:"+sdf.format(new Date())); } } }); t2.setName("线程2"); t2.start(); System.out.println("线程1状态:"+t1.getState()); System.out.println("线程2状态:"+t2.getState()); RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean(); String pidStr = runtimeMXBean.getName(); System.out.println("pidStr="+pidStr); int pid = Integer.parseInt(pidStr.split("@")[0]); System.out.println("当前程序的进程号pid="+pid); }}运行结果:线程1状态:RUNNABLE线程2状态:BLOCKEDpidStr=11548@C01-16120305-01当前程序的进程号pid=11548说明:线程1因为在synchronized里面死循环,那么对象sdf无法被释放锁,一直被线程1锁持有,所以Thread2永远也拿不到对象sdf资源,线程被阻塞,也就是BLOCKED;我们打印出来了该main进程的pid,为11548,接下来,我们用jstack -l 11548看一下堆栈日志。
打开idea下方的Terminal:
E:\mytestProject\springtest>jstack -l 115482020-10-14 14:10:22Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.71-b01 mixed mode):"DestroyJavaVM" prio=6 tid=0x0000000003652800 nid=0x2cc4 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None"线程2" prio=6 tid=0x00000000122f4000 nid=0x1c18 waiting for monitor entry [0x0000000013d7f000] java.lang.Thread.State: BLOCKED (on object monitor) at com.test.main.Test$2.run(Test.java:37) - waiting to lock <0x00000007ab8447a8> (a java.text.SimpleDateFormat) at java.lang.Thread.run(Thread.java:745) Locked ownable synchronizers: - None"线程1" prio=6 tid=0x00000000122f1000 nid=0x2fb8 runnable [0x0000000013c7f000] java.lang.Thread.State: RUNNABLE at com.test.main.Test$1.run(Test.java:22) - locked <0x00000007ab8447a8> (a java.text.SimpleDateFormat) at java.lang.Thread.run(Thread.java:745) Locked ownable synchronizers: - None说明:我们可以看到线程2的状态为:java.lang.Thread.State: BLOCKED (on object monitor)线程2处于等待拿锁:waiting to lock,锁对象为:java.text.SimpleDateFormat线程1的状态为:java.lang.Thread.State: RUNNABLE线程1处于上锁状态:locked,锁对象为:java.text.SimpleDateFormat
4)WAITING
从单词上来看,他是等待的意思,这里指的是没有超时的等待,简单的说,如果一个线程处于该WAITING状态,没有被唤醒或者他等待的线程没有结束,他会一直拿不到cpu资源和锁。他跟BOLCKED的区别就是:BLOCKED他只有拿到锁才会继续运行,但是WAITING可以主动唤醒或者他等待的线程运行结束之后,它就可以接着运行。 使线程进入WAITING状态的3个方法: 1.调用wait()方法 调用wait方法所在的线程进入等待,只能在synchronized块中使用,可以被synchronized锁住的对象锁唤醒。 实例代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 final Thread t1 = new Thread("线程1") { public void run() { synchronized (sdf) { try { System.out.println("线程1-wait准备wait,当前线程状态为:" + this.getState()); sdf.wait(); System.out.println("线程1-wait结束,当前线程状态为:" + this.getState()); } catch (Exception e) { e.printStackTrace(); } } } }; //线程1 Thread t2 = new Thread("线程2") { public void run() { synchronized (sdf) { System.out.println("线程1的此时的状态:"+t1.getState()); System.out.println("线程2-准备唤醒,当前线程状态为:" + this.getState()); sdf.notify(); System.out.println("线程2-唤醒结束,当前线程状态为:" + this.getState()); System.out.println("线程1的此时的状态:"+t1.getState()); } } }; t1.start(); t2.start(); RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean(); System.out.println(runtimeMXBean.getName().split("@")[0]); }}运行结果:线程1-wait准备wait,当前线程状态为:RUNNABLE线程1的此时的状态:WAITING线程2-准备唤醒,当前线程状态为:RUNNABLE线程2-唤醒结束,当前线程状态为:RUNNABLE线程1的此时的状态:BLOCKED线程1-wait结束,当前线程状态为:RUNNABLE结果分析:第一步:线程1进入synchronized块,拿到日期sdf对象的持有锁,然后调用sdf对象的wait方法,使当前线程也就是线程1进入WAITING状态,也就释放了sdf对象的持有锁(此时线程2处于BLOCKED状态,别问我怎么知道,不信你看BLOCKED篇)第二步:线程2拿到了sdf对象的持有锁,此时线程1依然处于WAITING状态,接着调用了sdf对象的notify方法,就会唤醒所有持有sdf对象锁的线程去重新拿锁(这里会唤醒线程1去尝试重新拿sdf的锁),但是发现sdf对象的锁现在依然还是被线程2持有,所以此时线程1已经进入阻塞状态BLOCKED第三部:线程持有sdf对象锁代码块继续执行,执行完成后,释放sdf对象锁,然后线程1从阻塞状态重新拿到刚刚释放的sdf对象锁,然后接着执行一开始没有执行的代码: System.out.println("线程1-wait结束,当前线程状态为:" + this.getState());
2.join()方法
线程如果调用了join方法,那么代表这个调用者进入阻塞执行,只有当这个调用者所在的线程执行完毕之后,才能接着执行下一个线程; 实例代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 final Thread t1 = new Thread("线程1") { public void run() { for (int i = 0 ;i < 100; i++){ System.out.println("线程1打印1到100,当前:"+i); } } }; //线程1 Thread t2 = new Thread("线程2") { public void run() { for (int i = 0 ;i < 20; i++){ System.out.println("线程2打印1到100,当前:"+i); } } }; t1.start(); t1.join(); t2.start(); t2.join(); for (int i = 0 ;i < 30; i++){ System.out.println("main线程打印1到100,当前:"+i); } }}
运行结果,按照线程1,2,main的顺序执行:
3.LockSupport.park() 使park方法被调用所在的线程进入WAITING状态,也就是先不执行他了,先去执行别的线程; 先来一段代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.LockSupport;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 final Thread t1 = new Thread("线程1") { public void run() { System.out.println("111"); LockSupport.park(); System.out.println("222"); } }; t1.start(); Thread.sleep(1000); System.out.println("main111"); System.out.println("线程1的状态:"+t1.getState()); System.out.println("main222"); }}运行结果:111main111线程1的状态:WAITINGmain222说明:1:先执行park之前2:线程1进入WAITING3:执行main的3个打印4:由于线程1没有被唤醒,所有没有后续日志
5)TIMED_WAITING
这个跟上文的WAITING类似,只不过多了一个时间参数,被称为超时等待。除了wait,join和park之外,还有sleep方法也能进入该状态; 1.wait(超时) 实例代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.LockSupport;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 final Thread t1 = new Thread("线程1") { public void run() { synchronized (this){ System.out.println("线程1进入wait前,状态为:"+this.getState()); try { long start = System.currentTimeMillis(); this.wait(10000); long ss = System.currentTimeMillis()-start; System.out.println("线程1结束wait状态为"+this.getState()+",共耗时"+ss+"ms"); } catch (InterruptedException e) { e.printStackTrace(); } } } }; t1.start(); Thread.sleep(1000); System.out.println("main111"); System.out.println("线程1进入wait之后的状态:"+t1.getState()); System.out.println("main222"); }}运行结果:线程1进入wait前,状态为:RUNNABLEmain111线程1进入wait之后的状态:TIMED_WAITINGmain222线程1结束wait状态为RUNNABLE,共耗时10000ms说明:1:线程1进入synchronized代码开,打印wait之前的状态为RUNNABLE2:线程1调用wait(10000),等待10秒钟3:主线程开始执行,打印main1114:主线程打印此时线程1的状态为:TIMED_WATTING5:主线程打印main2226:10秒钟之后,线程1自动唤醒,重新拿到自身对象锁,当前状态恢复成RUNNABLE,打印wait之后,耗时刚好就是10秒
再来看看join超时
2.join(带超时)
实例代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.LockSupport;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 final Thread t1 = new Thread("线程1") { public void run() { for (int i = 0; i < 10; i++) { System.out.println("run()中的i="+i); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } }; t1.start(); Thread.sleep(1000); System.out.println("main开始运行"); System.out.println("准备调用线程1的join方法,阻塞main线程3秒钟"); t1.join(3000); for (int i = 0; i < 5; i++) { System.out.println("main中的i="+i); } }}运行结果:run()中的i=0main开始运行准备调用线程1的join方法,阻塞main线程3秒钟run()中的i=1run()中的i=2run()中的i=3main中的i=0main中的i=1main中的i=2main中的i=3main中的i=4run()中的i=4run()中的i=5run()中的i=6run()中的i=7run()中的i=8run()中的i=9说明:1:线程1开始打印第一个数字0,睡眠1秒2:main开始执行,执行到调用线程1的join方法,开始阻塞main线程执行,main此时状态为TIMED_WAITING3:3秒之后,main线程被唤醒,线程1进行睡眠1秒,开始打印main线程的i4:接着打印线程1剩下的i
6)TERMINATED
一般执行完了线程的run方法之后,线程状态表示结束; 实例代码:package com.test.main;import sun.java2d.pipe.SpanShapeRenderer;import javax.net.ssl.ManagerFactoryParameters;import javax.sound.midi.Soundbank;import java.lang.management.ManagementFactory;import java.lang.management.RuntimeMXBean;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.LockSupport;public class Test { private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { //线程1 final Thread t1 = new Thread("线程1") { public void run() { System.out.println("线程1执行了run方法"); } }; t1.start(); Thread.sleep(1000); t1.join(); System.out.println("main线程开始执行..."); System.out.println("线程1执行run之后的状态为:"+t1.getState()); }}运行结果:线程1执行了run方法main线程开始执行...线程1执行run之后的状态为:TERMINATED说明:1:线程1开始阻塞执行,打印,线程1执行了run方法2:阻塞结束,main开始执行,此时线程1的状态为:TERMINATED
针对以上,来一张状态流程图:
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