Java高并发专题之36、线程6种状态详解
线程的状态有哪几种？他们之间是如何转换的？
目录
1、线程状态分类
线程一共有六种状态，分别为New、RUNNABLE、BLOCKED、WAITING、TIMED_WAITING、TERMINATED，同一时刻只有一种状态，通过线程的getState方法可以获取线程的状态。
2、状态详解
Thread的状态使用java.lang.Thread.State枚举表示。
2.1、状态1：NEW
当线程被创建出来还没有被调用start()时候的状态。
public class NewState { public static void main(String[] args) { Thread thread1 = new Thread(thread1); System.out.println(thread1.getState()); } } 输出
NEW
2.2、状态2：RUNNABLE
当线程被调用了start()，且处于等待操作系统分配资源（如CPU）、等待IO连接、正在运行状态，即表示Running状态和Ready状态。
注：不一定被调用了start()立刻会改变状态，还有一些准备工作，这个时候的状态是不确定的。
public class RunnableState { public static void main(String[] args) { Thread thread1 = new Thread(thread1); thread1.start(); System.out.println(thread1.getState()); } } 输出
RUNNABLE
2.3、状态3：BLOCKED
等待监视器锁而被阻塞的线程的线程状态，当进入synchronized块/方法或者在调用wait()被唤醒/超时之后重新进入synchronized块/方法，但是锁被其它线程占有，这个时候被操作系统挂起，状态为阻塞状态。
阻塞状态的线程，即使调用interrupt()方法也不会改变其状态。
下面看案例代码，thread1持有lock对象的锁一直没有释放，而thread2也想获取lock对象的锁，但是锁一直被thread1持有者，导致thread2被阻塞在@1处，此时thread2的状态就是BLOCKED状态。
import java.util.concurrent.TimeUnit; public class BlockedState { static String lock = 锁; public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { synchronized (lock) { //死循环导致thread1一直持有lock对象锁 while (true) ; } } }; thread1.start(); //休眠1秒，让thread1先启动 TimeUnit.SECONDS.sleep(1); Thread thread2 = new Thread(thread2) { @Override public void run() { synchronized (lock) { //@1 System.out.println(thread2); } } }; thread2.start(); System.out.println(thread1.state: + thread1.getState()); System.out.println(thread2.state: + thread2.getState()); } } 运行结果
thread1.state:RUNNABLE thread2.state:BLOCKED 2个线程的堆栈信息，线程堆栈信息中包含了线程的详细信息，如：线程状态、线程目前执行到哪段代码了
thread2 #13 prio=5 os_prio=0 tid=0x00000000281ec000 nid=0x878 waiting for monitor entry [0x0000000028dff000] java.lang.Thread.State: BLOCKED (on object monitor) at BlockedState$2.run(BlockedState.java:25) - waiting to lock <0x00000007176b2a20> (a java.lang.String) Locked ownable synchronizers: - None thread1 #12 prio=5 os_prio=0 tid=0x00000000281ea800 nid=0x5e50 runnable [0x0000000028cff000] java.lang.Thread.State: RUNNABLE at BlockedState$1.run(BlockedState.java:12) - locked <0x00000007176b2a20> (a java.lang.String) Locked ownable synchronizers: - None 2.4、状态4：WAITING
无条件等待，当线程调用wait()/join()/LockSupport.park()不加超时时间的方法之后所处的状态，如果没有被唤醒或等待的线程没有结束，那么将一直等待，当前状态的线程不会被分配CPU资源和持有锁.
简单理解：就是无限期等待。
导致线程处于WAITING有3中方式。
方式1：wait()
import java.util.concurrent.TimeUnit; public class WaitingState1 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { synchronized (WaitingState1.class) { try { //调用wait方法，让线程等待 WaitingState1.class.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } }; thread1.start(); //模拟休眠1秒，让thread1运行到wait方法处 TimeUnit.SECONDS.sleep(1); System.out.println(thread.state: + thread1.getState()); } } 输出
thread1.state:WAITING
线程thread1堆栈信息
thread1 #12 prio=5 os_prio=0 tid=0x0000000027a5d800 nid=0x1b48 in Object.wait() [0x0000000028dbe000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000007176adc68> (a java.lang.Class for WaitingState1) at java.lang.Object.wait(Object.java:502) at WaitingState1$1.run(WaitingState1.java:11) - locked <0x00000007176adc68> (a java.lang.Class for WaitingState1) Locked ownable synchronizers: - None 方式2：join()
public class WaitingState2 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { while (true) ; } }; thread1.start(); //join方法会让当前主线程等待thread1结束 thread1.join(); } } 上面代码会导致主线程处于WAITING状态，下面是主线程堆栈信息，第2行显示主线程处于WAITING状态
main #1 prio=5 os_prio=0 tid=0x00000000035a4000 nid=0x3fbc in Object.wait() [0x000000000305f000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000007176b0708> (a WaitingState2$1) at java.lang.Thread.join(Thread.java:1249) - locked <0x00000007176b0708> (a WaitingState2$1) at java.lang.Thread.join(Thread.java:1323) at WaitingState2.main(WaitingState2.java:14) Locked ownable synchronizers: - None 方式3：LockSupport.park()
import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.LockSupport; public class WaitingState3 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { LockSupport.park(); } }; thread1.start(); //模拟休眠1秒，让thread1运行到park方法处 TimeUnit.SECONDS.sleep(1); System.out.println(thread1.state: + thread1.getState()); } } 输出
thread1.state:WAITING
线程thread1堆栈信息
thread1 #12 prio=5 os_prio=0 tid=0x00000000287cc000 nid=0x3880 waiting on condition [0x000000002918f000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:304) at WaitingState3$1.run(WaitingState3.java:9) Locked ownable synchronizers: - None 2.5、状态5：TIMED_WAITING
有条件的等待，当线程调用sleep(睡眠时间)/wait(等待时间)/join(等待时间)/ LockSupport.parkNanos(等待时间)/LockSupport.parkUntil(等待时间)方法之后所处的状态，在指定的时间没有被唤醒或者等待线程没有结束，会被系统自动唤醒，正常退出。
简单点理解：有限期等待。
导致线程处于WAITING有5中方式。
方式1：sleep(睡眠时间)
import java.util.concurrent.TimeUnit; public class TimedWaitingState1 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { //休眠500秒 = 500000毫秒 try { Thread.sleep(500 * 1000); } catch (InterruptedException e) { e.printStackTrace(); } } }; thread1.start(); //模拟休眠1秒，让thread1运行到sleep方法处 TimeUnit.SECONDS.sleep(1); System.out.println(thread1.state: + thread1.getState()); } } 输出
thread1.state:TIMED_WAITING
线程thread1堆栈信息，堆栈信息中可以看出是线程sleep方法导致线程等待的
thread1 #12 prio=5 os_prio=0 tid=0x0000000027e1c000 nid=0x5c68 waiting on condition [0x000000002917f000] java.lang.Thread.State: TIMED_WAITING (sleeping) at java.lang.Thread.sleep(Native Method) at TimedWaitingState1$1.run(TimedWaitingState1.java:10) Locked ownable synchronizers: - None 方式2：wait(等待时间)
import java.util.concurrent.TimeUnit; public class TimedWaitingState2 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { synchronized (TimedWaitingState2.class) { try { //调用wait方法，让线程等待500秒 TimedWaitingState2.class.wait(500 * 1000); } catch (InterruptedException e) { e.printStackTrace(); } } } }; thread1.start(); //模拟休眠1秒，让thread1运行到wait方法处 TimeUnit.SECONDS.sleep(1); System.out.println(thread1.state: + thread1.getState()); } } 输出
thread1.state:TIMED_WAITING
线程thread1堆栈信息，堆栈信息中可以看出是线程wait方法导致线程等待的
thread1 #12 prio=5 os_prio=0 tid=0x0000000028571000 nid=0x4b80 in Object.wait() [0x0000000028f2e000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000007176ae0b8> (a java.lang.Class for TimedWaitingState2) at TimedWaitingState2$1.run(TimedWaitingState2.java:11) - locked <0x00000007176ae0b8> (a java.lang.Class for TimedWaitingState2) Locked ownable synchronizers: - None 方式3：join(等待时间)
public class TimedWaitingState3 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { while (true) ; } }; thread1.start(); //join方法会让当前主线程等待thread1结束，最长等待500s，如果500s thread1.join(500 * 1000); } } 主线程堆栈信息
main #1 prio=5 os_prio=0 tid=0x0000000003274000 nid=0x1204 in Object.wait() [0x00000000030ee000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000007176b0cf8> (a TimedWaitingState3$1) at java.lang.Thread.join(Thread.java:1257) - locked <0x00000007176b0cf8> (a TimedWaitingState3$1) at TimedWaitingState3.main(TimedWaitingState3.java:11) Locked ownable synchronizers: - None 方式4：LockSupport.parkNanos(等待时间)
import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.LockSupport; public class TimedWaitingState4 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { //等待500秒 LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(500)); } }; thread1.start(); //模拟休眠1秒，让thread1运行到parkNanos方法处 TimeUnit.SECONDS.sleep(1); System.out.println(thread1.state: + thread1.getState()); } } 输出
thread1.state:TIMED_WAITING
线程thread1堆栈信息
thread1 #12 prio=5 os_prio=0 tid=0x0000000028a1e000 nid=0x455c waiting on condition [0x00000000293ff000] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:338) at TimedWaitingState4$1.run(TimedWaitingState4.java:10) Locked ownable synchronizers: - None 方式5：LockSupport.parkUntil(等待时间)
import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.LockSupport; public class TimedWaitingState5 { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { //等待500秒 LockSupport.parkUntil(System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(500)); } }; thread1.start(); //模拟休眠1秒，让thread1运行到parkNanos方法处 TimeUnit.SECONDS.sleep(1); System.out.println(thread1.state: + thread1.getState()); } } 输出
thread1.state:TIMED_WAITING
线程thread1堆栈信息
thread1 #12 prio=5 os_prio=0 tid=0x00000000291b2000 nid=0x3cc0 waiting on condition [0x0000000029b8f000] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.parkUntil(LockSupport.java:372) at TimedWaitingState5$1.run(TimedWaitingState5.java:10) Locked ownable synchronizers: - None 2.6、状态6：TERMINATED
执行完了run()方法。其实这只是Java语言级别的一种状态，在操作系统内部可能已经注销了相应的线程，或者将它复用给其他需要使用线程的请求，而在Java语言级别只是通过Java代码看到的线程状态而已。
import java.util.concurrent.TimeUnit; public class TerminatedState { public static void main(String[] args) throws InterruptedException { Thread thread1 = new Thread(thread1) { @Override public void run() { System.out.println(Thread.currentThread()); } }; thread1.start(); //休眠1秒，等待thread1执行完毕 TimeUnit.SECONDS.sleep(1); System.out.println(thread1 state: + thread1.getState()); } } 输出
Thread[thread1,5,main] thread1 state:TERMINATED 3、状态转换图
这个图是本文的重点，反复看，消化理解！！！
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