java线程状态和线程调度
java线程的创建和启动
文章目录
- 多线程
- 线程的状态
- 线程调度
- 线程优先级
- 线程休眠
- 阻塞线程
- 线程礼让
- 线程调度练习
多线程
线程的状态
package Threads;public class MyThread5 implements Runnable {@Overridepublic void run() {System.out.println("线程正在运行，处于运行状态");try {System.out.println("线程开始休眠，处于阻塞状态");//线程休眠5SThread.sleep(5000);System.out.println("线程休眠结束，阻塞状态结束，再次进入就绪状态");} catch (InterruptedException e) {e.printStackTrace();System.out.println("线程中断");}}}package Test;import Threads.MyThread5;//测试线程的状态public class MyThread5Test {public static void main(String[] args) {Runnable runnable = new MyThread5();Thread t = new Thread(runnable);System.out.println("线程处于创建状态");t.start();System.out.println("线程处于就绪状态");}}
线程调度
线程优先级
由于线程之间的运行是通过抢占CPU的资源来进行的，线程调度指的是按照特定的机制为多个线程分配CPU的使用权。
线程的优先级由1-10表示，1表示最低，10最高，默认的优先级是5。优先级高的线程获得CPU的资源概率比较大.
尝试更改线程的优先级:
package Threads;//创建线程类，实现Runnable接口public class MyThread2 implements Runnable {@Overridepublic void run() {for (int i = 1; i <= 100; i++) {System.out.println(Thread.currentThread().getName() + ":" + i);}}}package Test;import Threads.MyThread2;//测试线程public class MyThread2Test {public static void main(String[] args) {//创建线程对象Runnable runnable = new MyThread2();Thread thread = new Thread(runnable, "mythread1");Thread thread1 = new Thread(runnable, "mythread2");//线程调度，设置线程优先级// thread1.setPriority(10);// thread.setPriority(1);thread1.setPriority(Thread.MAX_PRIORITY);thread.setPriority(Thread.MIN_PRIORITY);//启动线程thread.start();thread1.start();}}
线程休眠
线程调度的另一个方案是线程休眠。让线程展示睡眠指定的时长，线程会进入到阻塞状态，睡眠时间过后的线程会再进入可运行的状态。
方法是:
public static void sleep(long millis)
millis是休眠时长，以毫秒为单位，调用sleep()方法需要处理InterruptedException异常。
package Threads;//模拟线程休眠的过程public class Wait {public static void bySec(long s) {for (int i = 1; i <= 5; i++) {System.out.println(i+"秒");try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}}}public static void main(String[] args) {System.out.println("线程开始休眠");Wait.bySec(5);System.out.println("线程结束休眠");}}
阻塞线程
join()方法
等待该线程终止，等待加入的其他线程结束后在继续执行本线程package Threads;
public class MyThread6 implements Runnable {
@Overridepublic void run() {for (int i = 1; i <= 30; i++) {System.out.println(Thread.currentThread().getName() + ":" + i);}}
}
package Test;
import Threads.MyThread6;public class MyThread6Test {public static void main(String[] args) {//创建子线程对象tRunnable runnable = new MyThread6();Thread t = new Thread(runnable, "myThread");t.start();//主线程main做的事情for (int i = 1; i <= 20; i++) {System.out.println(Thread.currentThread().getName() + ":" + i);//当i = 5的时候，强制把t线程加入执行//线程调度:join()--等待线程终止，等待t线程执行结束后，main主线程再继续执行if (i == 5) {try {t.join();} catch (InterruptedException e) {e.printStackTrace();}}}}}
线程礼让
- yield()方法
暂停当前线程，允许其他具有相同优先级的线程获得运行机会，该线程处于就绪状态，不会转为阻塞状态。这是线程之间的礼让问题，只是提供一种可能，但是不能保证一定会礼让成功。
package Threads;public class MyThread7 implements Runnable {@Overridepublic void run() {for (int i = 0; i <= 4; i++) {System.out.println(Thread.currentThread().getName() + ":" + i);if (i == 3) {Thread.yield();}}}}package Test;import Threads.MyThread7;public class MyThread7Test {public static void main(String[] args) {Runnable runnable = new MyThread7();Thread t1 = new Thread(runnable, "线程A");Thread t2 = new Thread(runnable, "线程B");t1.start();t2.start();}}
线程调度练习
优先级问题
package Threads;
public class MyThread8 implements Runnable {
@Overridepublic void run() {}
}
package Test;
import Threads.MyThread8;
//获取和设置主线程和子线程的优先级
public class MyThread8Test {public static void main(String[] args) {//主线程Thread mainThread = Thread.currentThread();//子线程Thread myThread = new Thread(new MyThread8());System.out.println("默认的优先级");System.out.println("主线程名:" + mainThread.getName() + "优先级:" + mainThread.getPriority());System.out.println("子线程名:" + myThread.getName() + "优先级:" + myThread.getPriority());System.out.println("修改优先级后");mainThread.setPriority(Thread.MAX_PRIORITY);myThread.setPriority(Thread.MIN_PRIORITY);System.out.println("主线程名:" + mainThread.getName() + "优先级:" + mainThread.getPriority());System.out.println("子线程名:" + myThread.getName() + "优先级:" + myThread.getPriority());}
}
练习
需求：某一个科室一天需看普通号20个，特需号10个，特需号的看病时间是普通号的2倍。开始时普通号和特需号并行叫号，叫到特需号的概率比普通号的高。当普通号叫完第10号时，要求先看完全部的特需号再看普通号。
package Threads;
public class SpecialThread implements Runnable {
@Overridepublic void run() {for (int i = 1; i <= 10; i++) {System.out.println("特需号:" + i + "号病人正在看病");//线程休眠来表示看病的过程try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}}}
}
package Threads;
//模拟医院看病
public class CommonThread {public static void main(String[] args) {//当前线程--普通号//创建一个特需号的线程Thread special = new Thread(new SpecialThread());special.setPriority(Thread.MAX_PRIORITY);special.start();for (int i = 1; i <= 20; i++) {System.out.println("普通号:" + i + "号病人在看病");try {Thread.sleep(500);} catch (InterruptedException e) {e.printStackTrace();}if (i == 10) {try {special.join();} catch (InterruptedException e) {e.printStackTrace();}}}}
}
多线程数据共享问题
多个线程共享数据时，可能会引发数据的不安全问题。
package Threads;public class TicketThread implements Runnable {private int ticket = 10;//记录车票总数private int num = 0;//记录用户抢到了第几张票//用户抢票@Overridepublic void run() {while (true) {if (ticket <= 0) {break;}//有余票，则抢票//修改车票数:总票数在抢完票后减一张ticket--;//用户抢完票后，票数加一num++;//模拟网络延迟try {Thread.sleep(500);} catch (InterruptedException e) {e.printStackTrace();}//显示出票反馈给用户System.out.println(Thread.currentThread().getName() + "抢到了第" + num + "张票,剩余" + ticket + "张票");}}}package Test;import Threads.TicketThread;public class TicketThreadTest {public static void main(String[] args) {Runnable runnable = new TicketThread();Thread t1 = new Thread(runnable);Thread t2 = new Thread(runnable);Thread t3 = new Thread(runnable);System.out.println("各方开始抢票");t1.start();t2.start();t3.start();}}
java线程同步
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