【110期】面試官：Redis分布式鎖如何解決鎖超時問題？

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來自：www.jianshu.com/p/39b3570d3b56

一、前言

關(guān)于redis分布式鎖, 查了很多資料, 發(fā)現(xiàn)很多只是實現(xiàn)了最基礎(chǔ)的功能, 但是, 并沒有解決當鎖已超時而業(yè)務(wù)邏輯還未執(zhí)行完的問題, 這樣會導致: A線程超時時間設(shè)為10s(為了解決死鎖問題), 但代碼執(zhí)行時間可能需要30s, 然后redis服務(wù)端10s后將鎖刪除, 此時, B線程恰好申請鎖, redis服務(wù)端不存在該鎖, 可以申請, 也執(zhí)行了代碼, 那么問題來了, A、B線程都同時獲取到鎖并執(zhí)行業(yè)務(wù)邏輯, 這與分布式鎖最基本的性質(zhì)相違背: 在任意一個時刻, 只有一個客戶端持有鎖, 即獨享。

為了解決這個問題, 本文將用完整的代碼和測試用例進行驗證, 希望能給小伙伴帶來一點幫助

二、準備工作

壓測工具jmeter

https://pan.baidu.com/share/init?surl=NN0c0tDYQjBTTPA-WTT3yg
提取碼: 8f2a

redis-desktop-manager客戶端

https://pan.baidu.com/share/init?surl=NoJtZZZOXsk45aQYtveWbQ
提取碼: 9bhf

postman

https://pan.baidu.com/share/init?surl=28sGJk4zxoOknAd-47hE7w
提取碼: vfu7

也可以直接官網(wǎng)下載, 我這邊都整理到網(wǎng)盤了

需要postman是因為我還沒找到j(luò)meter多開窗口的辦法, 哈哈

三、說明

1、springmvc項目

2、maven依賴

????????
????????<dependency>
????????????<groupId>org.springframework.datagroupId>
????????????<artifactId>spring-data-redisartifactId>
????????????<version>1.6.5.RELEASEversion>
????????dependency>
????????<dependency>
????????????<groupId>redis.clientsgroupId>
????????????<artifactId>jedisartifactId>
????????????<version>2.7.3version>
????????dependency>

3、核心類

• 分布式鎖工具類: DistributedLock

• 測試接口類: PcInformationServiceImpl

• 鎖延時守護線程類: PostponeTask

四、實現(xiàn)思路

先測試在不開啟鎖延時線程的情況下, A線程超時時間設(shè)為10s, 執(zhí)行業(yè)務(wù)邏輯時間設(shè)為30s, 10s后, 調(diào)用接口, 查看是否能夠獲取到鎖, 如果獲取到, 說明存在線程安全性問題

同上, 在加鎖的同時, 開啟鎖延時線程, 調(diào)用接口, 查看是否能夠獲取到鎖, 如果獲取不到, 說明延時成功, 安全性問題解決

五、實現(xiàn)

1、版本01代碼

1)、DistributedLock

package?com.cn.pinliang.common.util;

import?com.cn.pinliang.common.thread.PostponeTask;
import?com.google.common.collect.Lists;
import?org.springframework.beans.factory.annotation.Autowired;
import?org.springframework.data.redis.core.RedisCallback;
import?org.springframework.data.redis.core.RedisTemplate;
import?org.springframework.stereotype.Component;
import?redis.clients.jedis.Jedis;

import?java.io.Serializable;
import?java.util.Collections;

@Component
public?class?DistributedLock?{

????@Autowired
????private?RedisTemplate?redisTemplate;

????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?=?"EX";
????//?解鎖腳本(lua)
????private?static?final?String?RELEASE_LOCK_SCRIPT?=?"if?redis.call('get',?KEYS[1])?==?ARGV[1]?then?return?redis.call('del',?KEYS[1])?else?return?0?end";

????/**
?????*?分布式鎖
?????*?@param?key
?????*?@param?value
?????*?@param?expireTime?單位:?秒
?????*?@return
?????*/
????public?boolean?lock(String?key,?String?value,?long?expireTime)?{
????????return?redisTemplate.execute((RedisCallback<Boolean>)?redisConnection?->?{
????????????Jedis?jedis?=?(Jedis)?redisConnection.getNativeConnection();
????????????String?result?=?jedis.set(key,?value,?SET_IF_NOT_EXIST,?SET_WITH_EXPIRE_TIME,?expireTime);
????????????if?(LOCK_SUCCESS.equals(result))?{
????????????????return?Boolean.TRUE;
????????????}
????????????return?Boolean.FALSE;
????????});
????}

????/**
?????*?解鎖
?????*?@param?key
?????*?@param?value
?????*?@return
?????*/
????public?Boolean?unLock(String?key,?String?value)?{
????????return?redisTemplate.execute((RedisCallback<Boolean>)?redisConnection?->?{
????????????Jedis?jedis?=?(Jedis)?redisConnection.getNativeConnection();
????????????Object?result?=?jedis.eval(RELEASE_LOCK_SCRIPT,?Collections.singletonList(key),?Collections.singletonList(value));
????????????if?(RELEASE_SUCCESS.equals(result))?{
????????????????return?Boolean.TRUE;
????????????}
????????????return?Boolean.FALSE;
????????});
????}

}

說明: 就2個方法, 加鎖解鎖, 加鎖使用jedis setnx方法, 解鎖執(zhí)行l(wèi)ua腳本, 都是原子性操作

2)、PcInformationServiceImpl

????public?JsonResult?add()?throws?Exception?{
????????String?key?=?"add_information_lock";
????????String?value?=?RandomUtil.produceStringAndNumber(10);
????????long?expireTime?=?10L;

????????boolean?lock?=?distributedLock.lock(key,?value,?expireTime);
????????String?threadName?=?Thread.currentThread().getName();
????????if?(lock)?{
????????????System.out.println(threadName?+?"?獲得鎖...............................");
????????????Thread.sleep(30000);
????????????distributedLock.unLock(key,?value);
????????????System.out.println(threadName?+?"?解鎖了...............................");
????????}?else?{
????????????System.out.println(threadName?+?"?未獲取到鎖...............................");
????????????return?JsonResult.fail("未獲取到鎖");
????????}

????????return?JsonResult.succeed();
????}

說明: 測試類很簡單, value隨機生成, 保證唯一, 不會在超時情況下解鎖其他客戶端持有的鎖

3)、打開redis-desktop-manager客戶端, 刷新緩存, 可以看到, 此時是沒有add_information_lock的key的

4)、啟動jmeter, 調(diào)用接口測試

設(shè)置5個線程同時訪問, 在10s的超時時間內(nèi)查看redis, add_information_lock存在, 多次調(diào)接口, 只有一個線程能夠獲取到鎖

redis

1-4個請求, 都未獲取到鎖

第5個請求, 獲取到鎖

OK, 目前為止, 一切正常, 接下來測試10s之后, A仍在執(zhí)行業(yè)務(wù)邏輯, 看別的線程是否能獲取到鎖

可以看到, 操作成功, 說明A和B同時執(zhí)行了這段本應(yīng)該獨享的代碼, 需要優(yōu)化。

2、版本02代碼

1)、DistributedLock

package?com.cn.pinliang.common.util;

import?com.cn.pinliang.common.thread.PostponeTask;
import?com.google.common.collect.Lists;
import?org.springframework.beans.factory.annotation.Autowired;
import?org.springframework.data.redis.core.RedisCallback;
import?org.springframework.data.redis.core.RedisTemplate;
import?org.springframework.stereotype.Component;
import?redis.clients.jedis.Jedis;

import?java.io.Serializable;
import?java.util.Collections;

@Component
public?class?DistributedLock?{

????@Autowired
????private?RedisTemplate?redisTemplate;

????private?static?final?Long?RELEASE_SUCCESS?=?1L;
????private?static?final?Long?POSTPONE_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?=?"EX";
????//?解鎖腳本(lua)
????private?static?final?String?RELEASE_LOCK_SCRIPT?=?"if?redis.call('get',?KEYS[1])?==?ARGV[1]?then?return?redis.call('del',?KEYS[1])?else?return?0?end";
????//?延時腳本
????private?static?final?String?POSTPONE_LOCK_SCRIPT?=?"if?redis.call('get',?KEYS[1])?==?ARGV[1]?then?return?redis.call('expire',?KEYS[1],?ARGV[2])?else?return?'0'?end";

????/**
?????*?分布式鎖
?????*?@param?key
?????*?@param?value
?????*?@param?expireTime?單位:?秒
?????*?@return
?????*/
????public?boolean?lock(String?key,?String?value,?long?expireTime)?{
????????//?加鎖
????????Boolean?locked?=?redisTemplate.execute((RedisCallback<Boolean>)?redisConnection?->?{
????????????Jedis?jedis?=?(Jedis)?redisConnection.getNativeConnection();
????????????String?result?=?jedis.set(key,?value,?SET_IF_NOT_EXIST,?SET_WITH_EXPIRE_TIME,?expireTime);
????????????if?(LOCK_SUCCESS.equals(result))?{
????????????????return?Boolean.TRUE;
????????????}
????????????return?Boolean.FALSE;
????????});

????????if?(locked)?{
????????????//?加鎖成功,?啟動一個延時線程,?防止業(yè)務(wù)邏輯未執(zhí)行完畢就因鎖超時而使鎖釋放
????????????PostponeTask?postponeTask?=?new?PostponeTask(key,?value,?expireTime,?this);
????????????Thread?thread?=?new?Thread(postponeTask);
????????????thread.setDaemon(Boolean.TRUE);
????????????thread.start();
????????}

????????return?locked;
????}

????/**
?????*?解鎖
?????*?@param?key
?????*?@param?value
?????*?@return
?????*/
????public?Boolean?unLock(String?key,?String?value)?{
????????return?redisTemplate.execute((RedisCallback<Boolean>)?redisConnection?->?{
????????????Jedis?jedis?=?(Jedis)?redisConnection.getNativeConnection();
????????????Object?result?=?jedis.eval(RELEASE_LOCK_SCRIPT,?Collections.singletonList(key),?Collections.singletonList(value));
????????????if?(RELEASE_SUCCESS.equals(result))?{
????????????????return?Boolean.TRUE;
????????????}
????????????return?Boolean.FALSE;
????????});
????}

????/**
?????*?鎖延時
?????*?@param?key
?????*?@param?value
?????*?@param?expireTime
?????*?@return
?????*/
????public?Boolean?postpone(String?key,?String?value,?long?expireTime)?{
????????return?redisTemplate.execute((RedisCallback<Boolean>)?redisConnection?->?{
????????????Jedis?jedis?=?(Jedis)?redisConnection.getNativeConnection();
????????????Object?result?=?jedis.eval(POSTPONE_LOCK_SCRIPT,?Lists.newArrayList(key),?Lists.newArrayList(value,?String.valueOf(expireTime)));
????????????if?(POSTPONE_SUCCESS.equals(result))?{
????????????????return?Boolean.TRUE;
????????????}
????????????return?Boolean.FALSE;
????????});
????}

}

說明: 新增了鎖延時方法, lua腳本, 自行腦補相關(guān)語法

2)、PcInformationServiceImpl不需要改動

3)、PostponeTask

package?com.cn.pinliang.common.thread;

import?com.cn.pinliang.common.util.DistributedLock;

public?class?PostponeTask?implements?Runnable?{

????private?String?key;
????private?String?value;
????private?long?expireTime;
????private?boolean?isRunning;
????private?DistributedLock?distributedLock;

????public?PostponeTask()?{
????}

????public?PostponeTask(String?key,?String?value,?long?expireTime,?DistributedLock?distributedLock)?{
????????this.key?=?key;
????????this.value?=?value;
????????this.expireTime?=?expireTime;
????????this.isRunning?=?Boolean.TRUE;
????????this.distributedLock?=?distributedLock;
????}

????@Override
????public?void?run()?{
????????long?waitTime?=?expireTime?*?1000?*?2?/?3;//?線程等待多長時間后執(zhí)行
????????while?(isRunning)?{
????????????try?{
????????????????Thread.sleep(waitTime);
????????????????if?(distributedLock.postpone(key,?value,?expireTime))?{
????????????????????System.out.println("延時成功...........................................................");
????????????????}?else?{
????????????????????this.stop();
????????????????}
????????????}?catch?(Exception?e)?{
????????????????e.printStackTrace();
????????????}
????????}
????}

????private?void?stop()?{
????????this.isRunning?=?Boolean.FALSE;
????}

}

說明: 調(diào)用lock同時, 立即開啟PostponeTask線程, 線程等待超時時間的2/3時間后, 開始執(zhí)行鎖延時代碼, 如果延時成功, add_information_lock這個key會一直存在于redis服務(wù)端, 直到業(yè)務(wù)邏輯執(zhí)行完畢, 因此在此過程中, 其他線程無法獲取到鎖, 也即保證了線程安全性

下面是測試結(jié)果

10s后, 查看redis服務(wù)端, add_information_lock仍存在, 說明延時成功

此時用postman再次請求, 發(fā)現(xiàn)獲取不到鎖

看一下控制臺打印

A線程在19:09:11獲取到鎖, 在10 * 2 / 3 = 6s后進行延時, 成功, 保證了業(yè)務(wù)邏輯未執(zhí)行完畢的情況下不會釋放鎖

A線程執(zhí)行完畢, 鎖釋放, 其他線程又可以競爭鎖

OK, 目前為止, 解決了鎖超時而業(yè)務(wù)邏輯仍在執(zhí)行的鎖沖突問題, 還很簡陋, 而最嚴謹?shù)姆绞竭€是使用官方的 Redlock 算法實現(xiàn), 其中 Java 包推薦使用 redisson, 思路差不多其實, 都是在快要超時時續(xù)期, 以保證業(yè)務(wù)邏輯未執(zhí)行完畢不會有其他客戶端持有鎖

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