【线程】详解线程状态（到底是五种还是六种）

原创已于 2023-03-09 09:28:11 修改

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#linq #java #p2p #多线程

于 2022-01-20 15:21:43 首次发布

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首先我们要知道，在传统（操作系统）的线程模型中线程被分为五种状态

在java线程中，线程被分为六种状态

传统线程模型（操作系统）中线程状态

线程的五种状态：

1.新建（new）

创建了一个新的线程对象

2.就绪（runnable）

调用线程的start()方法，处于就绪状态

3.运行（running）

获得了CPU时间片，执行程序代码

就绪状态是进入到运行状态的唯一入口

4.阻塞（block）

因为某种原因，线程放弃对CPU的使用权，停止执行，直到进入就绪状态在有可能再次被CPU调度

阻塞又分为三种：

1）等待阻塞：运行状态的线程执行wait方法，JVM会把线程放在等待队列中，使本线程进入阻塞状态。

2）同步阻塞：线程在获得synchronized同步锁失败，JVM会把线程放入锁池中，线程进入同步阻塞。对于锁池和等待池，可以看这篇文章

3）其他阻塞：调用线程的sleep()或者join()后，线程会进入道阻塞状态，当sleep超时或者join终止或超时，线程重新转入就绪状态

5.死亡（dead）

线程run()、main()方法执行结束，或者因为异常退出了run()方法，则该线程结束生命周期

死亡的线程不可再次复生

Java线程中的状态

通过查看Thread类的State方法，我们可以看到Java线程其实是六种状态

public enum State {
        /**
         * Thread state for a thread which has not yet started.
         */
        NEW,

        /**
         * Thread state for a runnable thread.  A thread in the runnable
         * state is executing in the Java virtual machine but it may
         * be waiting for other resources from the operating system
         * such as processor.
         */
        RUNNABLE,

        /**
         * Thread state for a thread blocked waiting for a monitor lock.
         * A thread in the blocked state is waiting for a monitor lock
         * to enter a synchronized block/method or
         * reenter a synchronized block/method after calling
         * {@link Object#wait() Object.wait}.
         */
        BLOCKED,

        /**
         * Thread state for a waiting thread.
         * A thread is in the waiting state due to calling one of the
         * following methods:
         * <ul>
         *   <li>{@link Object#wait() Object.wait} with no timeout</li>
         *   <li>{@link #join() Thread.join} with no timeout</li>
         *   <li>{@link LockSupport#park() LockSupport.park}</li>
         * </ul>
         *
         * <p>A thread in the waiting state is waiting for another thread to
         * perform a particular action.
         *
         * For example, a thread that has called <tt>Object.wait()</tt>
         * on an object is waiting for another thread to call
         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
         * that object. A thread that has called <tt>Thread.join()</tt>
         * is waiting for a specified thread to terminate.
         */
        WAITING,

        /**
         * Thread state for a waiting thread with a specified waiting time.
         * A thread is in the timed waiting state due to calling one of
         * the following methods with a specified positive waiting time:
         * <ul>
         *   <li>{@link #sleep Thread.sleep}</li>
         *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
         *   <li>{@link #join(long) Thread.join} with timeout</li>
         *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
         *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
         * </ul>
         */
        TIMED_WAITING,

        /**
         * Thread state for a terminated thread.
         * The thread has completed execution.
         */
        TERMINATED;
    }

我们可以看到线程实际上是分为六种状态的，既