java中线程状态

佚名 6年前 (2019-05-05) 随笔 889人围观抢沙发百度已收录

刚开始接触java时，就觉得多线程是一个障碍，不容易理解，当时选择了跳过，不过工作一段时间后，发现这块还是需要深入研究一下的，及时平时工作中不使用多线程，但一定会使用web容器，比如tomcat，也是会接触到多喜爱能成，况且现在工作中也是需要使用到多线程。首先从简单的开始，了解线程的状态，查看Thread源码，与getState方法在一起的有个枚举State，其包含了线程的所有状态

 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;
    }

通过以上代码了解到，线程有六种状态：NEW、RUNNABLE、BLOCKED、WAITING、TIMED_WAITING、TERMINATED

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根据个人理解，简单列出了各状态之间的转换

NEW到RUNNABLE状态不可回退

RUNNABLE到TERMINATED状态不可回退

代码验证NEW,RUNNABLE和TERMINATED状态

package com.demo;

public class ThreadTest {

    public static void main(String[] args) {
        Thread t = new Thread() {

            @Override
            public void run() {
                System.out.println("run");
            }
        };

        System.out.println(t.getState()); // NEW,还未调用start方法
        t.start();
        System.out.println(t.getState()); // RUNNABLE,调用了start方法，但线程还未结束

        try {
            // 等待线程结束，其实休眠毫秒级应该就可以结束
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(t.getState());// TERMINATED,线程结束

    }
}

输出结果

验证BLOCK与WAITING状态

package com.demo;

public class ThreadTest {

    public static void main(String[] args) {

        Runnable r = new Runnable() {

            @Override
            public void run() {
                synchronized (this) {
                    try {
                        Thread.sleep(50000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        };

        Thread t1 = new Thread(r, "Thread1");
        Thread t2 = new Thread(r, "Thread2");
        
        // 优先级数字范围为1到10，默认5，数字越小，优先级越高
        t1.setPriority(5);
        t2.setPriority(8);

        t1.start();
        t2.start();

    }
}