线程的状态

线程的六种状态：

一、源码

Thead.State 枚举类

public enum State {
    /**
     * Thread state for a thread which has not yet started.
     * 通过 new 关键字创建，但是还未调用 start 方法。这时的状态称为： NEW
     */
    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 （可运行）状态：
     *  可分为： Ready 、 Running 两种状态
     * 1.Ready: 线程已准备好，正在等待来自操作系统的其他资源，例如处理器（例如：线程调用了start方法、通过 notify/notifyAll 唤醒的线程 ）
     * 2.Running: 系统调度，当前线程抢占到资源，这时的状态称为：Running
     *
     */
    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 （阻塞）状态：
     * 1.线程 I/O 阻塞时（例如：去读取文件时，等待系统返回）的状态
     * 2.线程等待监视器锁而阻塞的线程（例如：要进入 synchronized 同步块或方法）的状态
     *
     */
    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 （等待）状态：
     * 由于调用以下方法之一，线程处于 WAITING 状态：
     * 1.调用 Object.wait()  方法，并且没有设置超时时间
     * 2.调用 Thread.join() 方法，并且没有设置超时时间
     * 3.调用 LockSupport.park() 方法
     *
     * 处于等待状态的线程正在等待另一个线程执行特定操作（进行唤醒）。
     * 例如：
     * 1.调用 Object.wait()  方法的线程，等待另外一个线程调用 Object.notify() / Object.notifyAll()
     * 2.调用 Thread.join()  方法的线程，等待指定的线程终止。
     * 3.调用 LockSupport.park() 方法的线程，等待另外一个线程调用 LockSupport.unpark()
     */
    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 （具有指定等待时间的等待线程的线程状态）状态：
     * 由于调用以下方法之一，线程处于 TIMED_WAITING 状态：
     * 1.调用 Thread.Sleep 方法
     * 2.调用 Object.wait(long) 方法，具有超时时间
     * 3.调用 Thread.join(long) 方法，具有超时时间
     * 4.LockSupport.parkNanos 方法
     * 5.LockSupport.parkUntil 方法
     *
     * 超过设置的时间之后自动唤醒，进入 RUNNABLE 状态
     *
     */
    TIMED_WAITING,
    /**
     * Thread state for a terminated thread.
     * The thread has completed execution.
     *
     * TERMINATED （完成）状态：
     * 终止线程的线程状态。线程已完成执行。
     */
    TERMINATED;
}

二、线程状态的切换