多线程线程安全问题

 1 /**
 2  * 继承Thread类
 3  * @date 2019/3/29 11:19
 4  */
 5 public class SimpleThread extends Thread{
 6 
 7     @Override
 8     public void run() {
 9         super.run();
10         Thread thread = Thread.currentThread();
11         System.out.println("Thread =>当前执行的线程为："+thread.getName());
12     }
13 }
14 
15 /**
16  * 实现Runnable接口
17  * @date 2019/3/29 11:28
18  */
19 public class SimpleRunnable implements Runnable {
20 
21     @Override
22     public void run() {
23          Thread thread = Thread.currentThread();
24          System.out.println("Runnable =>当前执行的线程为："+thread.getName());
25     }
26 }
27 
28 public class TestMain {
29 
30 
31     /**执行线程示例1*/
32     private static void callSimpleThread(){
33         int index=10;
34         for (int i = 0; i < index; i++) {
35              Thread thread=new SimpleThread();
36              thread.start();
37         }
38     }
39 
40     /**执行线程示例1*/
41     private static void callSimpleRunnable(){
42         int index=10;
43         for (int i = 0; i < index; i++) {
44             SimpleRunnable simpleRunnable=new SimpleRunnable();
45             new Thread(simpleRunnable,"Runnable-"+i).start();
46         }
47     }
48 
49     public static void main(String[] args) {
50 
51         callSimpleThread();
52 
53         callSimpleRunnable();
54     }
55 
56 }

多线程最容易产生的一个问题就是线程安全问题，下面使用一个卖票的例子来体现。

场景描述：现在有两个售票员，一共卖10张车票

 1 public class SellTicket extends Thread {
 2 
 3     private static int NUMBER = 10;
 4     public SellTicket(String name) {
 5         super(name);
 6     }
 7 
 8     @Override
 9     public void run() {
10         String s = "线程：" + Thread.currentThread().getName();
11 
12         while (NUMBER > 0) {
13             int i = NUMBER--;
14             System.out.println(s + " => 卖了第" + i + "号票");
15         }
16 
17         System.out.println(s + ",票已经卖完");
18         super.run();
19     }
20 
21 
22     public static void main(String[] args) {
23 
24         SellTicket thread1 = new SellTicket("售票员A");
25         thread1.start();
26 
27         SellTicket thread2 = new SellTicket("售票员B");
28         thread2.start();
29 
30     }
31 
32 }

方案一：使用同步代码解决
格式：synchronized(锁对象){需要被同步的代码}
锁对象可以为this锁，也可以自定义对象锁

方案二：使用同步函数解决
同步函数就是使用synchronized修饰一个函数

 1 public class SafetySellTicket extends Thread {
 2 
 3     private static int NUMBER = 10;
 4 
 5     @Override
 6     public  void run() {
 7         String s = "线程：" + Thread.currentThread().getName();
 8 
 9         while (NUMBER > 0) {
10             synchronized (this) {
11                 if (NUMBER > 0) {
12                     int i = NUMBER--;
13                     System.out.println(s + " => 卖了第" + i + "号票");
14                 } else {
15                     System.out.println(s + ",票已经卖完");
16                     break;
17                 }
18 
19             }
20         }
21         super.run();
22     }
23 
24 
25     public static void main(String[] args) {
26 
27         SafetySellTicket thread1 = new SafetySellTicket();
28         thread1.start();
29 
30         SafetySellTicket thread2 = new SafetySellTicket();
31         thread2.start();
32 
33     }
34 
35 }