死锁现象与解决策略-优快云博客

本文链接：https://blog.youkuaiyun.com/miniyuyu/article/details/79661938

1.背景

程序有两个入口，一个是从界面发起，一个是从MQ消息过来的，同时请求，请求的资源之间相互请求等待，形成死锁。表现：界面不响应。堆栈显示有死锁。

2.死锁原因：相互持有同步资源并相互等待。

package testsychronized;

/**
 * 模仿B级故障重现死锁现象。
 * */
public class TestDeadLock {
public static void main(String[] args) {
	new Thread1().start();
	new Thread2().start();
}
}

class Thread1 extends Thread {
	@Override
	public void run() {
		try {
			Web.get4Web();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}


class Thread2 extends Thread {
	@Override
	public void run() {
		try {
			LoadModel.loading();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

class Web {
	public static synchronized void get4Web() {
		try {
			System.out.println("Get  4 Web  Begaining...");
			LoadModel.getInfo();
			Thread.sleep(3000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("Get  4 Web   Ending...");
	}

	public static synchronized void setType() {
		try {
			System.out.println("Set  Type Begaining...");
			Thread.sleep(3000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("Set  Type Ending...");
	}
}

class LoadModel {
	public static synchronized void getInfo() {
		try {
			System.out.println("Get Info begaining...");
			Thread.sleep(3000);
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println("Get Info Endining...");
	}

	public static synchronized void loading() {
		try {
			System.out.println("Loading Info begaining...");
			Web.setType();
			Thread.sleep(3000);
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println("Loading Info Endining...");
	}
}

3. synchronizaed少用在方法上，减少锁的粒度，ReentrantLock或者CAS或者设计模式解决问题。