JAVA多线程基础

一.进程和线程概念

进程：程序运行的基本单元,进程包含线程
线程：是CPU调度和分派的基本单位,它是比进程更小的能独立运 行的基本单位

二.线程的实现方式

1. 继承Thread类

public class ThreadTest extends Thread {  　　public void run() {  　　 System.out.println("ThreadTest extends Thread");  　　}  }  

线程启动

ThreadTest thread = new ThreadTest ();thread .start()

1. 实现Runnable接口

public class ThreadTest  implements Runnable {  　　public void run() {  　　 System.out.println("ThreadTest  implements Runnable");  　　}  }  

线程启动

ThreadTest myThread = new ThreadTest();Thread thread = new Thread(myThread);thread.start();

三.线程的状态

线程的状态可分为五个状态：新建(new)、就绪(runnable)、运行(running)、等待/阻塞/睡眠(wait/blocked/sleep)、死亡(dead)

下图是线程状态图(图片转自https://my.oschina.net/mingdongcheng/blog/139263)

四.线程状态切换

1. 新建：表示新建一个线程对象
2. 就绪：线程创建后,就可以调用start方法,但是不立即执行,而是该进程在可运行进程池中,等待CPU调度使用
3. 运行：线程获得了cpu 时间片（timeslice）,即可执行代码
4. 等待：线程在运行中,调用的wait方法,当前线程进入等待队列;线程等待唤醒,需要调用notify/notifyAll
5. 阻塞：调用sleep和join都会是当前线程阻塞;sleep()在时间结束后,当前线程又回到就绪状态,等待CPU调度使用,join需要等调用join的线程执行完后,回到就绪状态,等待CPU调度使用
6. 死亡：线程run()、main() 方法执行结束，或者因异常退出了run()方法,线程整个生命周期结束

注：调用yield()会让当前线程回到就绪状态,让出cpu时间,让优先级高的线程执行

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五.线程通信

这里讲wait/notify的使用

public class ProducerConsumerInJava {     public static void main(String args[]) {         System.out.println("How to use wait and notify method in Java");         System.out.println("Solving Producer Consumper Problem");         Queue&lt buffer = new LinkedList();         int maxSize = 10;         Thread producer = new Producer(buffer, maxSize, "PRODUCER");         Thread consumer = new Consumer(buffer, maxSize, "CONSUMER");         producer.start();         consumer.start();         }     } class Producer extends Thread {         private Queue queue;         private int maxSize;         public Producer(Queue queue, int maxSize, String name){             super(name);            this.queue = queue;             this.maxSize = maxSize;         }         @Override public void run()         {             while (true)                 {                     synchronized (queue) {                         while (queue.size() == maxSize) {                             try {                                 System.out .println("Queue is full, " + "Producer thread waiting for " + "consumer to take something from queue");                                 queue.wait();                             } catch (Exception ex) {                                 ex.printStackTrace(); }                             }                             Random random = new Random();                             int i = random.nextInt();                             System.out.println("Producing value : " + i); queue.add(i); queue.notifyAll();                         }                     }                 }             }  class Consumer extends Thread {         private Queue queue;         private int maxSize;         public Consumer(Queue queue, int maxSize, String name){             super(name);             this.queue = queue;             this.maxSize = maxSize;         }         @Override public void run() {             while (true) {                 synchronized (queue) {                     while (queue.isEmpty()) {                         System.out.println("Queue is empty," + "Consumer thread is waiting" + " for producer thread to put something in queue");                         try {                             queue.wait();                         } catch (Exception ex) {                             ex.printStackTrace();                         }                     }                     System.out.println("Consuming value : " + queue.remove());                     queue.notifyAll();                 }             }         }     }

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