Java線程狀態

Java線程的狀態分爲NEW，RUNNABLE，BLOCKED,WAITING,TIMED_WAITING,TERMINATED，經過枚舉類java.lang.Thread.State定義。

    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;
    }

1.NEW表示線程建立後還沒有啓動

2.RUNNABLE表示線程處於可運行狀態，有可能正在被CPU執行或者等待CPU調度

3.BLOCKED表示阻塞狀態，代表線程正在等待監視器鎖。當線程正在等待監視器鎖進入synchronized塊/方法時，或調用Object.wait方法後從新進入synchronized塊/方法時。

4.WAITING表示無限期等待狀態。處於這種狀態的線程不會被分配CPU執行時間，它們要等待顯示的被其它線程喚醒。

如下方法會讓線程陷入無限期等待狀態：

（1）沒有設置timeout參數的Object.wait()

（2）沒有設置timeout參數的Thread.join()

（3）LockSupport.park()

5.TIMED_WAITING表示超時等待狀態。處於這種狀態的線程也不會被分配CPU執行時間，不過無需等待被其它線程顯示的喚醒，在必定時間以後它們會由系統自動的喚醒。

如下方法會讓線程進入TIMED_WAITING超時等待狀態：

（1）Thread.sleep()方法

（2）設置了timeout參數的Object.wait()方法

（3）設置了timeout參數的Thread.join()方法

（4）LockSupport.parkNanos()方法

（5）LockSupport.parkUntil()方法

6.TERMINATED表示結束狀態，表示線程已經結束執行