笔者看过网络上各种各样使用redis实现分布式锁的代码,要么错误,要么片段化,没有一个完整的例子,借这个周末给大家总结一下redis实现分布式锁的两种机制
自旋锁和排他锁
鉴于实现锁的方式不同,那么这里使用策略模式来组织代码
一、自旋锁
分布式锁抽象策略接口
package com.srr.lock;
/**
* @Description 分布式锁的接口
*/
abstract public interface DistributedLock {
/**
* 获取锁
*/
boolean lock();
/**
* 解锁
*/
void unlock();
}
自旋锁策略抽象类,使用模板方法模式构建
package com.srr.lock;
/**
* 自旋锁策略模板
*/
public abstract class SpinRedisLockStrategy implements DistributedLock {
private static final Integer retry = 50; //默认重试5次
private static final Long sleeptime = 100L;
protected String lockKey;
protected String requestId;
protected int expireTime;
private SpinRedisLockStrategy(){}
public SpinRedisLockStrategy(String lockKey, String requestId, int expireTime){
this.lockKey=lockKey;
this.requestId=requestId;
this.expireTime=expireTime;
}
/**
* 模板方法,搭建的获取锁的框架,具体逻辑交于子类实现
*/
@Override
public boolean lock() {
Boolean flag = false;
try {
for (int i=0;i<retry;i++){
flag = tryLock();
if(flag){
System.out.println(Thread.currentThread().getName()+"获取锁成功");
break;
}
Thread.sleep(sleeptime);
}
}catch (Exception e){
e.printStackTrace();
}
return flag;
}
/**
* 尝试获取锁,子类实现
*/
protected abstract boolean tryLock() ;
/**
* 解锁:删除key
*/
@Override
public abstract void unlock();
}
自旋锁实现子类
package com.srr.lock;
import redis.clients.jedis.Jedis;
import java.util.Collections;
/**
* 自旋锁
*/
public class SpinRedisLock extends SpinRedisLockStrategy{
private static final Long RELEASE_SUCCESS = 1L;
private static final String LOCK_SUCCESS = "OK";
private static final String SET_IF_NOT_EXIST = "NX";
private static final String SET_WITH_EXPIRE_TIME = "PX";
public SpinRedisLock(String lockKey, String requestId, int expireTime) {
super(lockKey,requestId, expireTime);
}
@Override
protected boolean tryLock() {
Jedis jedis = new Jedis("localhost", 6379); //创建客户端,1p和端口号
String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);
if (LOCK_SUCCESS.equals(result)) {
return true;
}
return false;
}
@Override
public void unlock() {
Jedis jedis = new Jedis("localhost", 6379); //创建客户端,1p和端口号
String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
Object result = jedis.eval(script, Collections.singletonList(lockKey), Collections.singletonList(requestId));
if (RELEASE_SUCCESS.equals(result)) {
System.out.println("lock is unlock");
}
}
}
至此,自旋锁方式实现分布式锁就完成了,下面来看排他锁阻塞的方式实现
二、排他锁
在实现之前需要大家搞懂一个概念,也就是redis的事件通知:
/**
* 键空间通知,所有通知以 keyspace@ 为前缀
* 键事件通知,所有通知以 keyevent@ 为前缀
* 所有命令都只在键真的被改动了之后,才会产生通知,比如删除foo会产生
* 键空间通知
* “pmessage”,"__ key*__ : * “,”__ keyspace@0__:foo",“set”
* 和键事件通知
* “pmessage”,"__ key*__ : *","__ keyevent@0__:set",“foo”
*/
搞懂概念之后,需要在redis的配置文件redis.conf中将其 notify-keyspace-events "KEA",默认为notify-keyspace-events "",这样才能启动redis的事件监听机制。
排它锁策略抽象类
package com.srr.lock;
import redis.clients.jedis.Jedis;
/**
* @Description 阻塞获取锁,模板类
*/
public abstract class BlockingRedisLockStrategy implements DistributedLock {
protected String lockKey;
protected String requestId;
protected int expireTime;
private BlockingRedisLockStrategy(){}
public BlockingRedisLockStrategy(String lockKey, String requestId,int expireTime){
this.lockKey=lockKey;
this.requestId=requestId;
this.expireTime=expireTime;
}
/**
* 模板方法,搭建的获取锁的框架,具体逻辑交于子类实现
* @throws Exception
*/
@Override
public final boolean lock() {
//获取锁成功
if (tryLock()){
System.out.println(Thread.currentThread().getName()+"获取锁成功");
return true;
}else{ //获取锁失败
//阻塞一直等待
waitLock();
//递归,再次获取锁
return lock();
}
}
/**
* 尝试获取锁,子类实现
*/
protected abstract boolean tryLock() ;
/**
* 等待获取锁,子类实现
*/
protected abstract void waitLock();
/**
* 解锁:删除key
*/
@Override
public abstract void unlock();
}
排他锁实现子类
package com.srr.lock;
import redis.clients.jedis.Jedis;
import java.util.Collections;
/**
* 排他锁,阻塞
*/
public class BlockingRedisLock extends BlockingRedisLockStrategy {
private static final Long RELEASE_SUCCESS = 1L;
private static final String LOCK_SUCCESS = "OK";
private static final String SET_IF_NOT_EXIST = "NX";
private static final String SET_WITH_EXPIRE_TIME = "PX";
public BlockingRedisLock(String lockKey, String requestId, int expireTime) {
super(lockKey,requestId, expireTime);
}
/**
* 尝试获取分布式锁
* @return 是否获取成功
*/
@Override
public boolean tryLock() {
Jedis jedis = new Jedis("localhost", 6379); //创建客户端,1p和端口号
String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);
if (LOCK_SUCCESS.equals(result)) {
return true;
}
return false;
}
@Override
public void waitLock() {
//判断key是否存在
Jedis jedis = new Jedis("localhost", 6379); //创建客户端,1p和端口号
KeyExpiredListener keyExpiredListener = new KeyExpiredListener();
/**
* 键空间通知,所有通知以 keyspace@ 为前缀
* 键事件通知,所有通知以 keyevent@ 为前缀
* 所有命令都只在键真的被改动了之后,才会产生通知,比如删除foo会产生
* 键空间通知
* “pmessage”,"__ key*__ : * “,”__ keyspace@0__:foo",“set”
* 和键事件通知
* “pmessage”,"__ key*__ : *","__ keyevent@0__:set",“foo”
*/
//如果要监听某个key的执行了什么操作,就订阅__ keyspace@0__,监听某种操作动了哪些key,就订阅__ keyevent@0__
//这里我们需要监听分布式锁的键被删除了,所以要监听删除动作"__keyspace@0__:"+key
jedis.psubscribe(keyExpiredListener, "__keyspace@0__:"+lockKey);
System.out.println("over");
}
/**
* 释放分布式锁
* @return 是否释放成功
*/
@Override
public void unlock() {
Jedis jedis = new Jedis("localhost", 6379); //创建客户端,1p和端口号
String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
Object result = jedis.eval(script, Collections.singletonList(lockKey), Collections.singletonList(requestId));
if (RELEASE_SUCCESS.equals(result)) {
System.out.println("lock is unlock");
}
}
}
redis事件监听类
package com.srr.lock;
import redis.clients.jedis.JedisPubSub;
/**
* redis 事件监听器
*/
public class KeyDelListener extends JedisPubSub {
public KeyDelListener(){
}
// 初始化订阅时候的处理
@Override
public void onPSubscribe(String pattern, int subscribedChannels) {
}
// 取得订阅的消息后的处理
@Override
public void onPMessage(String pattern, String channel, String message) {
System.out.println("message == "+message);
this.punsubscribe();
System.out.println("unsubscribe == "+message);
}
}
到这里排他锁的完整代码就写完了,其实对比一下,两者的区别在于lock的实现方式不同,笔者为了确保代码完整性就全部贴上了。
代码写完了那么给一个场景测试一下我们的代码有没有问题,请看下面的测试代码:
这里我们构建一个Lock工具类:
package com.srr.lock;
/**
* 锁工具类
*/
public class Lock {
/**
* 获取锁
*/
boolean lock(DistributedLock lock) {
return lock.lock();
};
/**
* 释放锁
*/
void unlock(DistributedLock lock) {
lock.unlock();
};
}
测试类:
package com.srr.lock;
import redis.clients.jedis.Jedis;
/**
* 测试场景
* count从1加到101
* 使用redis分布式锁在分布式环境下保证结果正确
*/
public class T {
volatile int count = 1;
public void inc(){
for(int i = 0;i<100;i++){
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
count++;
System.out.println("count == "+count);
}
}
public int getCount(){
return count;
}
public static void main(String[] args) {
final T t = new T();
final Lock lock = new Lock();
//final RedisLock redisLock = new BlockingRedisLock("","1",100000,jedis);
final DistributedLock distributedLock = new SpinRedisLock("test","1",100000);
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
if(lock.lock(distributedLock)){
t.inc();
System.out.println("t1 running");
System.out.println("t1 == count == "+ t.getCount());
lock.unlock(distributedLock);
}
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
if(lock.lock(distributedLock)) {
t.inc();
System.out.println("t2 running");
System.out.println("t2 == count == " + t.getCount());
lock.unlock(distributedLock);
}
}
});
t1.start();
t2.start();
}
}
测试结果:
image到这里,全部代码就完成了,如果想使用zookeeper实现分布式锁只需要抽象出一个策略类实现DistributedLock接口即可。是不是很方便呢。
来源:https://www.cnblogs.com/sx-bj-srr/p/distributedLock.html?utm_source=tuicool&utm_medium=referral
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