剑指Offer(线程)——线程的状态

通过Thread.State就可以看到线程的状态：

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;
    }

Java一共有六个状态：

1. 新建(New)

创建后尚未启动的线程的状态。

2. 运行(Runnable)

包含Running和Ready，线程可以在执行也可能在等CPU给其分配内存空间，.start()的线程处于Running状态，线程池中的线程就是Ready状态。

3. 无限期等待(Waiting)

不会被分配CPU执行空间需要显示的被唤醒。
比如：
没有设置Timeout参数的Object.wait()方法
没有设置Timeout参数的Thread.join()方法
LockSuport.park()方法

4. 限期等待(Time Waiting)

在一定时间后由系统自动唤醒。
比如：
Thread.sleep()方法
设置Timeout参数的Object.wait()方法
设置Timeout参数的Thread.join()方法
LockSuport.parkNanos()方法
LockSuport.parkUntil()方法

5. 阻塞(Blocked)

等待获取排它锁

6. 结束(Terminated)

已经终止线程的状态，线程已经结束执行。