基于Redis实现分布式锁
时间:2022-07-24
本文章向大家介绍基于Redis实现分布式锁,主要内容包括其使用实例、应用技巧、基本知识点总结和需要注意事项,具有一定的参考价值,需要的朋友可以参考一下。
基于Redis实现分布式锁
一. 基本原理
- 基于Redis的setnx命令,如果设置成功,则表示当前进程(线程)获取锁成功,否则说明有其他进程已经获取了锁,需进行等待
- setnx 的key为需要加锁的资源名称(实例中为方法名),value为业务唯一的id
- 加锁时需制定锁的过期时间,避免锁未正常释放而导致的死锁问题
- 加锁时需设置等待超时时间,避免等待时间过长导致系统性能下降
- 释放锁时,与Redis中的value与当前的业务id进行对比,符合才执行释放操作
二. 代码实现
- 加锁的核心操作
/**
* @Auther: ZhangShenao
* @Date: 2019/3/8 10:29
* @Description:分布式锁信息
*/
@Getter
@Setter
public class LockInfo {
//业务唯一id,作为锁的value
private String transactionId;
//锁的key
private String lockKey;
//重试次数
private int retryTimes;
public static LockInfo valueOf(String transactionId, String lockKey) {
LockInfo info = new LockInfo();
info.transactionId = transactionId;
info.lockKey = lockKey;
info.retryTimes = 0;
return info;
}
public void addRetryTimes(){
++retryTimes;
}
}
/**
* @Auther: ZhangShenao
* @Date: 2019/3/8 10:26
* @Description:基于Redis实现的分布式锁
*/
@Component
public class RedisLock {
@Autowired
private StringRedisTemplate redisTemplate;
private ValueOperations<String, String> opsForValue;
private ThreadLocal<String> localTransactionId = new ThreadLocal<>();
@PostConstruct
private void init() {
opsForValue = redisTemplate.opsForValue();
}
public Optional<LockInfo> tryLock(String lockKey, long timeoutMillis, long expireSeconds) throws InterruptedException {
Assert.isTrue(timeoutMillis > 0L, "timeout must be positive!!");
Assert.isTrue(expireSeconds > 0L, "expire must be positive!!");
String transactionId = UUID.randomUUID().toString();
localTransactionId.set(transactionId);
LockInfo lockInfo = LockInfo.valueOf(transactionId, lockKey);
for (long startTime = System.currentTimeMillis(); System.currentTimeMillis() - startTime < timeoutMillis; lockInfo.addRetryTimes()) {
Boolean success = opsForValue.setIfAbsent(lockKey, transactionId);
if (Boolean.TRUE.equals(success)) {
redisTemplate.expire(lockKey, expireSeconds, TimeUnit.SECONDS);
System.err.println(String.format("Thread fetch lock. transactionId: %s, lockKey: %s, retryTimes: %s", lockInfo.getTransactionId(), lockKey, lockInfo.getRetryTimes()));
return Optional.of(lockInfo);
}
Thread.sleep(20L);
}
//timeout
System.err.println(String.format("Thread fetch lock timeout!! transactionId: %s, lockKey: %s", lockInfo.getTransactionId(), lockKey));
return Optional.empty();
}
public void release(String lockKey) {
String transactionId = Optional.ofNullable(opsForValue.get(lockKey)).orElseThrow(() -> new IllegalStateException("Lock Expired!! key: " + lockKey));
if (!transactionId.equalsIgnoreCase(localTransactionId.get())) {
throw new IllegalStateException("Thread try to release lock, but lock is not held by this thread!! threadId: " + Thread.currentThread().getId() + ", lockKey: " + lockKey);
}
redisTemplate.delete(lockKey);
System.err.println(String.format("Thread release lock. transactionId: %s, lockKey: %s", transactionId, lockKey));
}
}
- 基于Spring,开发自定义注解和切面,简化对方法加锁的操作
/**
* @Auther: ZhangShenao
* @Date: 2019/3/8 14:13
* @Description:自定义Lock,标记在方法上,用于指定哪些方法需要自动加Redis锁
*/
@Target(value = {ElementType.METHOD})
@Retention(value = RetentionPolicy.RUNTIME)
public @interface Lock {
String lockKey() default "";
long expireSeconds();
long timeoutSeconds();
}
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
import java.util.Optional;
/**
* @Auther: ZhangShenao
* @Date: 2019/3/8 14:05
* @Description:Redis锁切面,拦截标记了@Lock注解的方法,为其执行自动加锁和释放锁的操作
*/
@Aspect
@Component
public class RedisLockAspect {
@Autowired
private RedisLock redisLock;
@Around("@annotation(lock)")
public Object addLockForMethods(ProceedingJoinPoint point, Lock lock) throws Throwable {
Optional<LockInfo> lockInfo = Optional.empty();
String lockKey = generateLockKey(point, lock);
Object result = null;
try {
lockInfo = redisLock.tryLock(lockKey, lock.expireSeconds(), lock.timeoutSeconds());
result = point.proceed();
return result;
} catch (Exception e) {
e.printStackTrace();
} finally {
lockInfo.ifPresent(l -> redisLock.release(lockKey));
}
return result;
}
private String generateLockKey(ProceedingJoinPoint point, Lock lock) {
if (StringUtils.hasText(lock.lockKey())) {
return lock.lockKey();
}
MethodSignature signature = (MethodSignature) point.getSignature();
String methodName = signature.getMethod().getName();
String className = signature.getMethod().getDeclaringClass().getCanonicalName();
return methodName + "-" + className;
}
}
- 测试
/**
* @Auther: ZhangShenao
* @Date: 2019/3/8 14:28
* @Description:
*/
@Service
public class DemoService {
@Lock(expireSeconds = 60L, timeoutSeconds = 5L)
public String demoTask() {
return "Do demo task...";
}
}
/**
* @Auther: ZhangShenao
* @Date: 2019/3/8 13:49
* @Description:
*/
@SpringBootApplication
@Import(RedisConfig.class)
@EnableAspectJAutoProxy
public class RedisLockApplication {
public static void main(String[] args) {
ConfigurableApplicationContext applicationContext = SpringApplication.run(RedisLockApplication.class, args);
DemoService demoService = applicationContext.getBean(DemoService.class);
ExecutorService executorService = Executors.newFixedThreadPool(5);
for (int i = 0; i < 10; i++) {
System.err.println(demoService.demoTask());
}
executorService.shutdown();
}
}
结果:
Thread fetch lock. transactionId: 47aa449b-e0b7-407f-b861-52b06668f36e, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 47aa449b-e0b7-407f-b861-52b06668f36e, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: e5ce6b1e-2b02-40a3-aa2b-4ffb00e43f92, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: e5ce6b1e-2b02-40a3-aa2b-4ffb00e43f92, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: 9bde0756-614f-4a97-b57e-87b6dcabf763, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 9bde0756-614f-4a97-b57e-87b6dcabf763, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: 81154275-05de-401d-8f83-1a68ad0f7c3f, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 81154275-05de-401d-8f83-1a68ad0f7c3f, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: 1005e5b7-d1b8-4934-8e31-ceafa2fed891, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 1005e5b7-d1b8-4934-8e31-ceafa2fed891, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: 56eb7b87-dd23-41d3-becc-2058b3b113c1, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 56eb7b87-dd23-41d3-becc-2058b3b113c1, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: b4d46d03-341b-486d-aa1d-878ec56c1272, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: b4d46d03-341b-486d-aa1d-878ec56c1272, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: 8e48df53-a430-422e-90ee-bf90d5f2d455, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 8e48df53-a430-422e-90ee-bf90d5f2d455, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: 1a6963bc-869c-498c-95a1-279eb2b201e3, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: 1a6963bc-869c-498c-95a1-279eb2b201e3, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
Thread fetch lock. transactionId: ff78fe9a-9c49-44e2-b5f7-b7dccd3b792c, lockKey: demoTask-william.redis.lock.DemoService, retryTimes: 0
Thread release lock. transactionId: ff78fe9a-9c49-44e2-b5f7-b7dccd3b792c, lockKey: demoTask-william.redis.lock.DemoService
Do demo task...
可以看到,通过加锁,线程以同步方式顺序执行。
三. 待改进
- 加锁时和setnx操作和expire操作应该保证原子性,可以考虑在程序中执行Lua脚本
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