【java高性能编程基础】- java中线程的六种状态,线程状态变化的几种类型

x33g5p2x  于2022-01-04 转载在 Java  
字(5.4k)|赞(0)|评价(0)|浏览(380)

从源码看Thread中定义的六种线程状态

Thread类位于java.lang包下,在Thread类中有一个枚举类型State,State中定义了线程的六种状态。源码如下:

java.lang.Thread.State

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;
    }

6中线程状态:

  • 1、NEW
    尚未启动的线程的线程状态。
  • 2、RUNNABLE
    可运行线程的线程状态。
    可运行的线程状态正在Java虚拟机中执行,但它可能等待操作系统的其他资源如处理器。
  • 3、BLOCKED
    线程阻塞等待监视器锁定的线程状态。
    处于synchronized同步代码块或方法中被阻塞。
  • 4、WAITING
    等待线程的线程状态。
    处于等待状态的线程正在等待另一个线程执行特定的操作。
  • 5、TIMED_WAITING
    具有指定等待时间的等待线程的线程状态。
  • 6、TERMINATED
    终止线程的线程状态。
    线程正常完成执行或者出现异常。

注:线程在给定时间点只能处于一种状态。这些状态是虚拟机状态,不反映任何操作系统线程状态。

调用getState方法可以得到当前线程的状态。

public class ThreadTest {
    public static void main(String[] args) {
        Thread thread1 = new MyThread();

        System.out.println("thread1的线程状态:" + thread1.getState());
        thread1.start();
        System.out.println("thread1的线程状态:" + thread1.getState());

    }
}

class MyThread extends Thread{
    @Override
    public void run() {
        System.out.println(this.getName() + " is running。。。");
    }
}

线程状态的变化

1.线程正常运行结束的状态变化

public class ThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("当前线程正在执行-------");
                System.out.println("线程正在执行时的线程状态:" + Thread.currentThread().getState().toString());
            }
        });
        System.out.println("创建线程后,调用start前的线程状态:" + thread1.getState().toString());
        thread1.start();
        Thread.sleep(2000L); // 等待thread1执行结束,再看状态
        System.out.println("---等待两秒,线程执行结束后的状态:" + thread1.getState().toString());
        //thread1.start(); //当线程终止之后,再进行调用,会抛出IllegalThreadStateException异常
    }
}

程序运行结果显示:

  • 当一个线程被创建时(还未调用start方法)处于NEW状态;
  • 调用start方法后,线程开始执行,此时线程处于RUNNABLE状态;
  • 线程继续执行,一段时间后,线程正常执行结束,此时线程处于TERMINATED状态。
    (新建 -> 运行 -> 终止,NEW-> RUNNABLE-> TERMINATED)

注意:当线程执行结束之后,再进行调用,会抛出IllegalThreadStateException异常

2.线程执行过程中等待一段时间再继续执行结束的状态变化

public class ThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("当前线程正在执行-------,需要花费两秒时间------");
                try {   // 将线程2移动到等待状态,2s后自动唤醒
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("线程正在执行时的线程状态:" + Thread.currentThread().getState().toString());
            }
        });
        System.out.println("创建线程后,调用start前的线程状态:" + thread2.getState().toString());
        thread2.start();
        Thread.sleep(200L); // 等待200毫秒,再看状态
        System.out.println("等待200毫秒(线程还没执行结束),线程的状态:" + thread2.getState().toString());
        Thread.sleep(3000L); // 再等待3秒,让thread2执行完毕,再看状态
        System.out.println("等待3秒(线程执行结束),线程的状态:" + thread2.getState().toString());
    }
}

程序运行结果显示:

  • 当一个线程被创建时(还未调用start方法)处于NEW状态;
  • 调用start方法后,线程开始执行,此时线程处于RUNNABLE状态;
  • 当线程运行过程中需要等待一段时间时,线程进入TIMED_WAITING状态
  • 线程继续执行,一段时间后,线程正常执行结束,此时线程处于TERMINATED状态。
    (新建 -> 运行 -> 等待 -> 运行 -> 终止,NEW-> RUNNABLE->TIMED_WAITING->RUNNABLE-> TERMINATED)

3.线程执行过程中等待其他线程被阻塞,然后继续执行到结束的状态变化

public class ThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (ThreadState.class) {
                    System.out.println("当前线程正在执行-------");
                    System.out.println("线程正在执行时的线程状态:" + Thread.currentThread().getState().toString());
                }
            }
        });
        synchronized (ThreadState.class) {
            System.out.println("没调用start方法,thread3当前状态:" + thread3.getState().toString());
            thread3.start();
            System.out.println("调用start方法,thread3当前状态:" + thread3.getState().toString());
            Thread.sleep(200L);
            System.out.println("等待200毫秒,线程遇到锁被堵塞时的状态:" + thread3.getState().toString());
        }
        Thread.sleep(3000L); // 再等待3秒,让thread3执行完毕,再看状态
        System.out.println("等待3秒,线程抢到锁并执行结束时的状态:" + thread3.getState().toString());
    }
}

程序运行结果显示:

  • 当一个线程被创建时(还未调用start方法)处于NEW状态;
  • 调用start方法后,线程开始执行,此时线程处于RUNNABLE状态;
  • 当线程遇到锁被堵塞时线程进入BLOCKED状态
  • 线程继续执行,一段时间后,线程正常执行结束,此时线程处于TERMINATED状态。
    (新建 -> 运行 -> 阻塞 -> 运行 -> 终止,NEW-> RUNNABLE->BLOCKED->RUNNABLE-> TERMINATED)

相关文章