死锁

死锁是指：两个或两个以上的进程在执行过程中，由于竞争资源，或者由于彼此通信而造成的一种阻塞的现象。若无外力作用。他们都无法运行下去

小孩抢玩具（死锁）

package com.Luoking.Thread;
 
public class Deadlock {
    public static void main(String[] args) {
        playTools boy1 = new playTools("boy1","excavator");
        playTools boy2 = new playTools("boy2","gun");
 
        new Thread(boy1).start();
        new Thread(boy2).start();
    }
}
 
//枪
class gun {
}
 
//挖掘机
class excavator {
}
 
//两个小孩玩玩具
class playTools implements Runnable {
    //保证玩具都只有一个 static
    private static gun gun = new gun();
    private static excavator excavator = new excavator();
 
    //小孩名字
    String name;
    //小孩手上原先的玩具；
    String tool;
 
    //构造有参函数
    public playTools(String name, String tool) {
        this.name = name;
        this.tool = tool;
    }
 
    @Override
    public void run() {
        try {
            play();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
 
    public void play() throws InterruptedException {
        if (tool.equals("excavator")) {
            synchronized (excavator) {
                System.out.println(name + " get " + "excavator" + " play 2 S");
                Thread.sleep(2000);
                synchronized (gun) {
                    System.out.println(name + " get " + "gun");
                }
            }
        } else {
            synchronized (gun) {
                System.out.println(name + " get " + "gun" + " play 2 S");
                Thread.sleep(2000);
                synchronized (excavator) {
                    System.out.println(name + " get " + "excavator");
                }
            }
        }
 
    }
 
}

解决死锁问题
当需要另一个对象时，需要释放已有对象的锁

package com.Luoking.Thread;
 
public class Deadlock {
    public static void main(String[] args) {
        playTools boy1 = new playTools("boy1", "excavator");
        playTools boy2 = new playTools("boy2", "gun");
 
        new Thread(boy1).start();
        new Thread(boy2).start();
    }
}
 
//枪
class gun {
}
 
//挖掘机
class excavator {
}
 
//两个小孩玩玩具
class playTools implements Runnable {
    //保证玩具都只有一个 static
    private static gun gun = new gun();
    private static excavator excavator = new excavator();
 
    //小孩名字
    String name;
    //小孩手上原先的玩具；
    String tool;
 
    //构造有参函数
    public playTools(String name, String tool) {
        this.name = name;
        this.tool = tool;
    }
 
    @Override
    public void run() {
        try {
            play();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
 
    public void play() throws InterruptedException {
        if (tool.equals("excavator")) {
            synchronized (excavator) {
                System.out.println(name + " get " + "excavator" + " play 2 S");
                Thread.sleep(2000);
            }
            synchronized (gun) {
                System.out.println(name + " get " + "gun");
            }
        } else {
            synchronized (gun) {
                System.out.println(name + " get " + "gun" + " play 2 S");
                Thread.sleep(2000);
            }
            synchronized (excavator) {
                System.out.println(name + " get " + "excavator");
            }
        }
 
    }
 
}