Java并发编程之线程知识三：线程的状态

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java.lang.Thread内部描述线程状态的枚举类的源代码：

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;
}

线程的状态有如下几种：

NEW（初始化），
RUNNABLE（可运行的），
BLOCKED（锁定或阻塞），
WAITING（等待），
TIMED_WAITING（定时等待），
TERMINATED（结束）；

获取当前线程的状态

public State getState() {
	// get current thread state 获取当前线程的线程状态
	return sun.misc.VM.toThreadState(threadStatus);
}

状态流程图

 线程状态流转描述

线程创建出来就是new的状态。

start方法调用之后状态变成runnable,可以执行，如果cpu把时间片切过来就可以执行。

runnable执行完成则变成terminated，或者中断的时候。

runnable如果遇到有锁的方法，在等待的时候则是阻塞blocked的状态

如果调用wait或者join的方法，则变成waiting状态，

如果调用带时间参数的wait或者join,则变成time_waiting。