Java同步和死锁的实例分析

深碍√TFBOYSˉ_ 2022-07-30 20:00 168阅读 0赞

Java线程同步的简单示例

public class SameStep { 
        public static void main(String[] args) {
            MyThread mt1 = new MyThread();
            Thread t1 = new Thread(mt1);
            Thread t2 = new Thread(mt1);
            Thread t3 = new Thread(mt1);
            t1.start();
            t2.start();
    
        }
    
    }
    
    class MyThread implements Runnable { 
        private int ticket = 10;
    
        @Override
        public void run() {
            // TODO Auto-generated method stub
            for (int i = 0; i <= 100; i++) {
                synchronized (this) {
                    if (ticket > 0)
                        System.out.println("ticket = " + (--ticket));
                }
    
            }
    
        }
    
    }

Java线程死锁的示例

大概的思路：两个线程T1和T2，两把锁L1和L2，现在T1先拿到锁L1，然后sleep()一段时间，我们知道sleep()是不会释放锁资源的。然后如果这段时间线程T2拿到锁L2，也sleep()一段时间的话，那么等到两个线程都醒过来的话，那么将互相等待对方释放锁资源而僵持下去，陷入死锁。mark的作用就是让T1和T2获得不同的锁。

class Dog {
        public void sys() {
            System.out.println("如果你给我骨头，我就给你鱼");
        }
    
        public void get() {
            System.out.println("我拿到骨头了");
        }
    }
    
    class Cat {
        public void sys() {
            System.out.println("如果你给我鱼，我就给你骨头");
        }
    
        public void get() {
            System.out.println("我拿到鱼了");
        }
    }
    
    public class DeadLock implements Runnable { 
        public static Cat cat = new Cat();
        public static Dog dog = new Dog();
        boolean mark = false;
    
        @Override
        public void run() {
            // TODO Auto-generated method stub
            if (mark) {
                // 当前的Cat说
                synchronized (cat) {
                    cat.sys();
                    // 等待拿鱼
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    synchronized (dog) {
                        cat.get();
                    }
                }
            } else {
                synchronized (dog) {
                    // 当前的Dog说
                    dog.sys();
                    // 等待拿骨头
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    synchronized (cat) {
                        dog.get();
                    }
    
                }
            }
    
        }
    
        public static void main(String args[]) {
            DeadLock d1 = new DeadLock();
            DeadLock d2 = new DeadLock();
            d1.mark = false;
            d2.mark = true;
            Thread t1 = new Thread(d1);
            Thread t2 = new Thread(d2);
            t1.start();
            t2.start();
    
        }
    
    }