Java线程状态

1、Java线程6中状态

Java线程一共分为6种状态，如下所示

• NEW：新建状态
• RUNNABLE：就绪状态
• BLOCKED：阻塞状态
• WAITING：等待状态
• TIMED_WAITING：限时等待状态
• TERMINATED：结束状态

2、Tread类中State枚举定义的6种状态

通过Tread中的State枚举查看这六种状态的定义，如下所示：

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:
         * 

         *   
{@link Object#wait() Object.wait} with no timeout
         *   
{@link #join() Thread.join} with no timeout
         *   
{@link LockSupport#park() LockSupport.park}
         * 
         *
         * 
A thread in the waiting state is waiting for another thread to
         * perform a particular action.
         *
         * For example, a thread that has called Object.wait()
         * on an object is waiting for another thread to call
         * Object.notify() or Object.notifyAll() on
         * that object. A thread that has called Thread.join()
         * 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:
         * 

         *   
{@link #sleep Thread.sleep}
         *   
{@link Object#wait(long) Object.wait} with timeout
         *   
{@link #join(long) Thread.join} with timeout
         *   
{@link LockSupport#parkNanos LockSupport.parkNanos}
         *   
{@link LockSupport#parkUntil LockSupport.parkUntil}
         * 
         */
        TIMED_WAITING,

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

3、各种状态的图解

各种状态图解，如下图所示：

4、各种状态的解释

• NEW状态 表示刚刚创建的线程，这种线程还没开始执行。等到线程的start()方法调用时，才表示线程开始执行。

• RUNNABLE状态 表示线程所需的一切资源都已经准备好了。处于就绪状态的线程，只是说明此线程已经做好了被运行的准备，随时等待CPU调度执行，而并不是说调用了start()方法，这个线程就会被立即运行。

• BLOCKED状态 如果线程在执行过程中遇到了synchronized或者Lock，那么就会进入到阻塞状态。处于阻塞状态的线程会放弃对CPU的使用权，停止执行，直到次线程进入到了就绪的状态，才会有机会再次被CPU调用运行。

• WAITING状态 如果线程被调用了没有超时时间的wait方法，那么会进入无限等待状态。直到被notify通知才可以继续执行。

• TIMED_WAITING状态 与WAITING状态相似，区别是，在有限的时间内进行线程等待。