解决线程安全问题的第二种方式：Lock(锁)

￡神魔★判官ぃ 2021-12-05 19:45 187阅读 0赞

### Lock(JDK5新增) ###

private Lock lock=new ReentrantLock();  
try\{  
lock.lock();//加锁  
//需要被同步的代码  
\}finally\{  
lock.unlock();//释放锁  
\}  
1.首先模拟一个多线程(售票)的情境，此时存在重票或者错票的安全问题

class SubThread implements  Runnable{ 
    
        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，票号为: "+ticket);
                    ticket--;
                }else{ 
                    break;
                }
            }
        }
    }
    
    public class LockTest { 
        public static void main(String[] args) { 
            SubThread subThread=new SubThread();
            Thread t1=new Thread(subThread);
            Thread t2=new Thread(subThread);
            Thread t3=new Thread(subThread);
            t1.setName("窗口1");
            t2.setName("窗口2");
            t3.setName("窗口3");
            t1.start();
            t2.start();
            t3.start();
        }
    }

2.Lock锁方式解决线程安全问题，Lock是接口，我们利用其子类ReentrantLock重入锁  
主要采用三步,(1)实例化ReentrantLock(2)在try部分调用lock()方法加锁(3)在finally部分调用unlock()方法解锁，解锁后线程继续重新争夺cpu

class SubThread implements  Runnable{ 
    
        private int ticket=100;
    
        //1.实例化ReentrantLock
        private ReentrantLock lock = new ReentrantLock();
    
        @Override
        public void run() { 
            while(true){ 
    
                //2.调用lock();代码块就被锁住了
                lock.lock();
                try { 
                    if (ticket > 0) { 
                        try { 
                            Thread.sleep(100);
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName() + ": 售票，票号为: " + ticket);
                        ticket--;
                    } else { 
                        break;
                    }
                }finally { 
                    //3.调用方法unlock();解锁
                    lock.unlock();
                }
            }
        }
    }
    
    public class LockTest { 
        public static void main(String[] args) { 
            SubThread subThread=new SubThread();
            Thread t1=new Thread(subThread);
            Thread t2=new Thread(subThread);
            Thread t3=new Thread(subThread);
            t1.setName("窗口1");
            t2.setName("窗口2");
            t3.setName("窗口3");
            t1.start();
            t2.start();
            t3.start();
        }
    }