java解决多线程并发安全问题的三种方式

待我称王封你为后i 2022-10-01 06:41 192阅读 0赞

# java并发线程带来的安全问题 #

#### 场景模拟 ####

> 创建三个线程模拟三个售票窗口,来同时出售一百张票

#### 代码 ####

package com.shemuel;
    
    /** * @Author: dengshaoxiang * @Date: 2019/6/11 15:46 * @Description: */
    public class ThreadDemo { 
        public static void main(String[] args) { 
            MyTicket ticket = new MyTicket();
            new Thread(ticket,"一号窗口").start();
            new Thread(ticket,"二号窗口").start();
            new Thread(ticket,"三号窗口").start();
        }
    }
    class MyTicket implements Runnable{ 
        // 一百张票
        private int ticket = 100;
        @Override
        public void run() { 
            while (true) { 
                if (ticket > 0) { 
                    try { 
                        Thread.sleep(100);
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "售票完成,余票 : " + --ticket);
                }
            }
        }
    }

运行程序,结果:

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70]

可以看到结果数据产生了问题.

#### 解决方法 ####

##### 方法一 :同步代码块 #####

代码:

package com.shemuel;
    
    /** * @Author: dengshaoxiang * @Date: 2019/6/11 15:46 * @Description: */
    public class ThreadDemo { 
        public static void main(String[] args) { 
            MyTicket ticket = new MyTicket();
            new Thread(ticket,"一号窗口").start();
            new Thread(ticket,"二号窗口").start();
            new Thread(ticket,"三号窗口").start();
        }
    }
    class MyTicket implements Runnable{ 
        // 一百张票
        private int ticket = 100;
        @Override
        public void run() { 
            sellTicket();
        }
        public synchronized void sellTicket() { 
            while (true) { 
                if (ticket > 0) { 
                    try { 
                        Thread.sleep(50);
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "售票完成,余票 : " + --ticket);
                }
            }
        }
    }

结果:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70 1]

##### 方法二 : 同步方法 #####

代码:

package com.shemuel;
    
    /**
     * @Author: dengshaoxiang
     * @Date: 2019/6/11 15:46
     * @Description:
     */
    public class ThreadDemo {
        public static void main(String[] args) {
            MyTicket ticket = new MyTicket();
            new Thread(ticket,"一号窗口").start();
            new Thread(ticket,"二号窗口").start();
            new Thread(ticket,"三号窗口").start();
        }
    }
    class MyTicket implements Runnable{
        // 一百张票
        private int ticket = 100;
        @Override
        public void run() {
            synchronized (this){
                while (true) {
                    if (ticket > 0) {
                        try {
                            Thread.sleep(50);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName() + "售票完成,余票 : " + --ticket);
                    }
                }
            }
        }
    }

结果:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70 2]

##### 方法三 : Lock同步锁 #####

代码:

package com.shemuel;
    
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /** * @Author: dengshaoxiang * @Date: 2019/6/11 15:46 * @Description: */
    public class ThreadDemo { 
        public static void main(String[] args) { 
            MyTicket ticket = new MyTicket();
            new Thread(ticket,"一号窗口").start();
            new Thread(ticket,"二号窗口").start();
            new Thread(ticket,"三号窗口").start();
        }
    }
    class MyTicket implements Runnable{ 
        private Lock lock = new ReentrantLock();
        // 一百张票
        private int ticket = 100;
        @Override
        public void run() { 
            while (true) { 
                lock.lock();
                try { 
                    if (ticket > 0) { 
                        try { 
                            Thread.sleep(50);
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName() + "售票完成,余票 : " + --ticket);
                    }
                }finally { 
                    lock.unlock();
                }
            }
        }
    }

结果:

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70 3]  
**注意**:lock 一定要在finally代码块里解锁.  
[查看更多例子和源码请戳这里][Link 1]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70]: /images/20220119/01f39318509f422a80bd8ca1b084cc9d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70 1]: /images/20220119/f7466a1f752548b1af00058e24d3b419.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70 2]: /images/20220119/ae6e162639be49afbb7ef67a10456b86.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1MjQ5MzQy_size_16_color_FFFFFF_t_70 3]: /images/20220119/1a24d1d7fb6a4432aa1874eed660e302.png
[Link 1]: https://github.com/ShemuelDeng/demo