Java线程状态介绍

原创：转载需注明原创地址 https://www.cnblogs.com/fanerwei222/p/11867086.html

Java 线程状态介绍:

Java官方文档中对Java线程的几种状态做了说明, 说明如下;

public static enum Thread.State
extends Enum<Thread.State>

A thread state. A thread can be in one of the following states:

  NEW
    A thread that has not yet started is in this state.
  RUNNABLE
    A thread executing in the Java virtual machine is in this state.
  BLOCKED
    A thread that is blocked waiting for a monitor lock is in this state.
  WAITING
    A thread that is waiting indefinitely for another thread to perform a particular action is in this state.
  TIMED_WAITING
    A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.
  TERMINATED
    A thread that has exited is in this state.

A thread can be in only one state at a given point in time. These states are virtual machine states which do not reflect any operating system thread states.

以这个文档来进行一点说明:

Java 线程共有6个状态:

新建(NEW)
可运行(RUNNABLE)
阻塞(BLOCKED)
等待(WAITING)
超时等待(TIMED_WAITING)
终止(TERMINATED)

各个状态的生成时机和介绍:

1. 新建(NEW)

new Thread() --> 新建

2. 可运行(RUNNABLE)

　　2.1 就绪
        Thread.start() --> 开始线程 --> 到达可运行仓库的门口排队就绪
        Object.notify() --> 从等待/超时等待状态回到就绪队列
        Object.notifyAll() --> 从等待/超时等待状态回到就绪队列
        LockSupport.unpark(Thread) --> 从等待/超时等待状态回到就绪队列
        Thread.yield() --> 从运行状态回到就绪队列
        获取到 synchronized(Object)块/方法 中的对象锁 --> 从阻塞状态回到就绪队列

    2.2 运行
        就绪中的线程等待系统调度(得到CPU)成功之后 --> 开始运行 --> 运行中(占用CPU, 占用锁)

3. 阻塞(BLOCKED)

等待获取 synchronized(Object)块/方法 中的对象锁时 --> 阻塞
Thread.sleep(long timeout) --> 从运行状态进入阻塞状态(释放CPU, 占用锁)

4. 等待(WAITING)

Object.wait() --> 从运行状态进入等待状态(释放CPU, 释放锁)
Thread.join() --> 从运行状态进入等待状态
LockSupport.park() --> 从运行状态进入等待状态

5. 超时等待(TIMED_WAITING)

Object.wait(long timeout) --> 从运行状态进入超时等待状态(释放CPU, 释放锁)
Thread.sleep(long timeout) --> 从运行状态进入超时等待状态(释放CPU, 占用锁)
Thread.join(long timeout) --> 从运行状态进入超时等待状态
LockSupport.parkNanos(long timeout) --> 从运行状态进入超时等待状态
LockSupport.parkUntil(long timeout) --> 从运行状态进入超时等待状态

6. 终止(TERMINATED)

Thread.run()执行完毕之后 --> 终止

线程中断说明: interrupt()

线程在等待状态或者阻塞状态, 调用了线程的 interrupt() 方法, 会有以下3个过程:
        1. 中断标记会立刻被标记为 true;
        2. 随后由于是阻塞状态, 中断标记 true 会被清除 --> 所以又变成了false;
        3. 最后抛出 InterruptedException 异常.