本篇內(nèi)容介紹了“怎么理解redis中的分布式鎖”的有關(guān)知識(shí)，在實(shí)際案例的操作過程中，不少人都會(huì)遇到這樣的困境，接下來就讓小編帶領(lǐng)大家學(xué)習(xí)一下如何處理這些情況吧！希望大家仔細(xì)閱讀，能夠?qū)W有所成！
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Redis 分布式鎖
大家項(xiàng)目中都會(huì)使用到分布式鎖把，通常用來做數(shù)據(jù)的有序操作場景，比如一筆訂單退款（如果可以退多次的情況）?；蛘哂脩舳喽讼聠?。【相關(guān)推薦：Redis視頻教程】
Maven 依賴
我主要是基于 Spring-Boot 2.1.2 + Jedis 進(jìn)行實(shí)現(xiàn)
4.0.0
org.springframework.boot
spring-boot-starter-parent
2.1.2.RELEASE
cn.edu.cqvie
redis-lock
1.0-SNAPSHOT
UTF-8
1.8
2.9.0
5.0.7
org.springframework.boot
spring-boot-autoconfigure
org.springframework.data
spring-data-redis
redis.clients
jedis
${redis.version}
org.springframework.boot
spring-boot-starter-logging
org.slf4j
log4j-over-slf4j
org.springframework.boot
spring-boot-starter-test
test
org.springframework.boot
spring-boot-maven-plugin
配置文件
application.properties 配置文件內(nèi)容如下：
spring.redis.host=127.0.0.1
spring.redis.port=6379
spring.redis.password=
spring.redis.timeout=30000
spring.redis.jedis.pool.max-active=8
spring.redis.jedis.pool.min-idle=2
spring.redis.jedis.pool.max-idle=4
logging.level.root=INFO
接口定義
接口定義，對于鎖我們核心其實(shí)就連個(gè)方法 lock 和 unlock.
public interface RedisLock {
long TIMEOUT_MILLIS = 30000;
int RETRY_MILLIS = 30000;
long SLEEP_MILLIS = 10;
boolean tryLock(String key);
boolean lock(String key);
boolean lock(String key, long expire);
boolean lock(String key, long expire, long retryTimes);
boolean unlock(String key);
}分布式鎖實(shí)現(xiàn)
我的實(shí)現(xiàn)方式是通過 setnx 方式實(shí)現(xiàn)了，如果存在 tryLock 邏輯的話，會(huì)通過 自旋 的方式重試
// AbstractRedisLock.java 抽象類
public abstract class AbstractRedisLock implements RedisLock {
@Override
public boolean lock(String key) {
return lock(key, TIMEOUT_MILLIS);
}
@Override
public boolean lock(String key, long expire) {
return lock(key, TIMEOUT_MILLIS, RETRY_MILLIS);
}
}
// 具體實(shí)現(xiàn)
@Component
public class RedisLockImpl extends AbstractRedisLock {
private Logger logger = LoggerFactory.getLogger(getClass());
@Autowired
private RedisTemplate redisTemplate;
private ThreadLocal threadLocal = new ThreadLocal();
private static final String UNLOCK_LUA;
static {
StringBuilder sb = new StringBuilder();
sb.append("if redis.call(\"get\",KEYS[1]) == ARGV[1] ");
sb.append("then ");
sb.append(" return redis.call(\"del\",KEYS[1]) ");
sb.append("else ");
sb.append(" return 0 ");
sb.append("end ");
UNLOCK_LUA = sb.toString();
}
@Override
public boolean tryLock(String key) {
return tryLock(key, TIMEOUT_MILLIS);
}
public boolean tryLock(String key, long expire) {
try {
return !StringUtils.isEmpty(redisTemplate.execute((RedisCallback) connection -> {
JedisCommands commands = (JedisCommands) connection.getNativeConnection();
String uuid = UUID.randomUUID().toString();
threadLocal.set(uuid);
return commands.set(key, uuid, "NX", "PX", expire);
}));
} catch (Throwable e) {
logger.error("set redis occurred an exception", e);
}
return false;
}
@Override
public boolean lock(String key, long expire, long retryTimes) {
boolean result = tryLock(key, expire);
while (!result && retryTimes-- > 0) {
try {
logger.debug("lock failed, retrying...{}", retryTimes);
Thread.sleep(SLEEP_MILLIS);
} catch (InterruptedException e) {
return false;
}
result = tryLock(key, expire);
}
return result;
}
@Override
public boolean unlock(String key) {
try {
List keys = Collections.singletonList(key);
List args = Collections.singletonList(threadLocal.get());
Long result = redisTemplate.execute((RedisCallback) connection -> {
Object nativeConnection = connection.getNativeConnection();
if (nativeConnection instanceof JedisCluster) {
return (Long) ((JedisCluster) nativeConnection).eval(UNLOCK_LUA, keys, args);
}
if (nativeConnection instanceof Jedis) {
return (Long) ((Jedis) nativeConnection).eval(UNLOCK_LUA, keys, args);
}
return 0L;
});
return result != null && result > 0;
} catch (Throwable e) {
logger.error("unlock occurred an exception", e);
}
return false;
}
}測試代碼
最后再來看看如何使用吧. (下面是一個(gè)模擬秒殺的場景)
@RunWith(SpringRunner.class)
@SpringBootTest
public class RedisLockImplTest {
private Logger logger = LoggerFactory.getLogger(getClass());
@Autowired
private RedisLock redisLock;
@Autowired
private StringRedisTemplate redisTemplate;
private ExecutorService executors = Executors.newScheduledThreadPool(8);
@Test
public void lock() {
// 初始化庫存
redisTemplate.opsForValue().set("goods-seckill", "10");
List futureList = new ArrayList<>();
for (int i = 0; i < 100; i++) {
futureList.add(executors.submit(this::seckill));
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
// 等待結(jié)果，防止主線程退出
futureList.forEach(action -> {
try {
action.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
});
}
public int seckill() {
String key = "goods";
try {
redisLock.lock(key);
int num = Integer.valueOf(Objects.requireNonNull(redisTemplate.opsForValue().get("goods-seckill")));
if (num > 0) {
redisTemplate.opsForValue().set("goods-seckill", String.valueOf(--num));
logger.info("秒殺成功，剩余庫存：{}", num);
} else {
logger.error("秒殺失敗，剩余庫存：{}", num);
}
return num;
} catch (Throwable e) {
logger.error("seckill exception", e);
} finally {
redisLock.unlock(key);
}
return 0;
}
}總結(jié)
本文是 Redis 鎖的一種簡單的實(shí)現(xiàn)方式，基于 jedis 實(shí)現(xiàn)了鎖的重試操作。
但是缺點(diǎn)還是有的，不支持鎖的自動(dòng)續(xù)期，鎖的重入，以及公平性（目前通過自旋的方式實(shí)現(xiàn)，相當(dāng)于是非公平的方式）。
“怎么理解Redis中的分布式鎖”的內(nèi)容就介紹到這里了，感謝大家的閱讀。如果想了解更多行業(yè)相關(guān)的知識(shí)可以關(guān)注創(chuàng)新互聯(lián)網(wǎng)站，小編將為大家輸出更多高質(zhì)量的實(shí)用文章！
當(dāng)前標(biāo)題：怎么理解Redis中的分布式鎖
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