多线程学习笔记三 - 多线程死锁

多线程死锁：
　　死锁的常见情形之一：同步的嵌套。

public class DeadLock {
        public static void main(String[] args) throws InterruptedException {
            Customer cus = new Customer();
            Thread t1 = new Thread(cus);
            Thread t2 = new Thread(cus);
            t1.start();
            Thread.sleep(5);
            cus.flag = false;
            t2.start();
        }
    }
    class Bank2{
        private double sumMoney;
        
        public double getSumMoney() {
            return sumMoney;
        }
    
        public void setSumMoney(double sumMoney) {
            this.sumMoney = sumMoney;
        }
    
        public void add(double money){
            sumMoney += money;
            System.out.println(Thread.currentThread().getName()+"save:"+money+"   Bank2 has "+sumMoney);
        }
    }
    class Customer implements Runnable{
        Bank2 b = new Bank2();
        public boolean flag = true;
        Object obj = new Object();
        @Override
        public void run() {
            if(flag){
                while(true){
                    if(b.getSumMoney() < 100000){
                        synchronized(obj){
                            this.Operation();
                        }
                    }else{break;}
                }
            }else{
                while(true){
                    if(b.getSumMoney() < 100000){
                        this.Operation();
                    }else{break;}
                }
            }
            
        }
        public synchronized void Operation(){
            synchronized (obj) {
                b.add(1000);
                System.out.println("======function=====");;
            }
        }
    }

运行结果：

======function=====
Thread-1save:1000.0 Bank2 has 34000.0
======function=====
Thread-1save:1000.0 Bank2 has 35000.0
======function=====
Thread-1save:1000.0 Bank2 has 36000.0
======function=====
Thread-1save:1000.0 Bank2 has 37000.0
======function=====
Thread-1save:1000.0 Bank2 has 38000.0
======function=====
到38000时候发生了死锁。

　

　死锁小实例：（面试时候用）

　　

public class DeadLockTest {
        public static void main(String[] args) throws InterruptedException {
            MyThread mt1 = new MyThread();
            Thread t1 = new Thread(mt1);
            Thread t2 = new Thread(mt1);
            t1.start();
            Thread.sleep(1);
            mt1.flag = false;
            t2.start();
        }
    }
    
    class MyThread implements Runnable{
        public boolean flag = true ;
        @Override
        public void run() {
            while(true){
                if(flag){
                    synchronized(LockObject.obja){
                        try {
                            Thread.sleep(10);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName()+"if===obja");
                        synchronized(LockObject.objb){
                            System.out.println(Thread.currentThread().getName()+"if===objb");    
                        }
                    }
                }else{
                    synchronized(LockObject.objb){
                        try {
                            Thread.sleep(10);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName()+"else===obja");
                        synchronized(LockObject.obja){
                            System.out.println(Thread.currentThread().getName()+"else===objb");    
                        }
                    }
                }
            }
        }
        
    }
    class LockObject{
        public static final Object obja = new Object();
        public static final Object objb = new Object();
    }    

 　　在我后面的笔记五中，还有对另外一种死锁的形式的介绍，并且介绍了JDK1.5对synchronized同步锁的替代-->Lock接口，虽然出现了替代，但是因为synchronized

　　 同步锁和同步函数的简单性，并且它也能解决工作中的大部分死锁情况，所以synchronized同步锁的应用还是非常的广泛。