How to use Redis+Lua script to implement the anti-swipe function of the counter interface

[Implementation process]

1. Problem analysis

If the set command is set, but when setting the expiration time, the network jitters If the setting is not successful due to other reasons, a dead counter (similar to a deadlock) will occur;

2. Solution

Redis Lua is a good solution. Use a script to make set The command and expire command are executed together with Redis without being interfered with, which guarantees atomic operations to a large extent;

Why is it said that atomic operations are guaranteed to a large extent but not completely? Because problems may occur when Redis is executed internally, but the probability is very small; even for small-probability events, there are corresponding solutions, such as solving deadlocks. An idea worth referring to: Preventing deadlocks will store the lock value as a time Stamp, even if the expiration time is not set, when judging whether to lock, you can add it to see if the value exceeds a set time from now. If it exceeds, delete it and reset the lock.

3. Code transformation

1. Implementation of Redis Lua lock

package han.zhang.utils;
 
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.core.script.DigestUtils;
import org.springframework.data.redis.core.script.RedisScript;
import java.util.Collections;
import java.util.UUID;
public class RedisLock {
    private static final LogUtils logger = LogUtils.getLogger(RedisLock.class);
    private final StringRedisTemplate stringRedisTemplate;
    private final String lockKey;
    private final String lockValue;
    private boolean locked = false;
    /**
     * 使用脚本在redis服务器执行这个逻辑可以在一定程度上保证此操作的原子性
     * （即不会发生客户端在执行setNX和expire命令之间，发生崩溃或失去与服务器的连接导致expire没有得到执行，发生永久死锁）
     * <p>
     * 除非脚本在redis服务器执行时redis服务器发生崩溃，不过此种情况锁也会失效
     */
    private static final RedisScript<Boolean> SETNX_AND_EXPIRE_SCRIPT;
    static {
        StringBuilder sb = new StringBuilder();
        sb.append("if (redis.call(&#39;setnx&#39;, KEYS[1], ARGV[1]) == 1) then\n");
        sb.append("\tredis.call(&#39;expire&#39;, KEYS[1], tonumber(ARGV[2]))\n");
        sb.append("\treturn true\n");
        sb.append("else\n");
        sb.append("\treturn false\n");
        sb.append("end");
        SETNX_AND_EXPIRE_SCRIPT = new RedisScriptImpl<>(sb.toString(), Boolean.class);
    }
    private static final RedisScript<Boolean> DEL_IF_GET_EQUALS;
        sb.append("if (redis.call(&#39;get&#39;, KEYS[1]) == ARGV[1]) then\n");
        sb.append("\tredis.call(&#39;del&#39;, KEYS[1])\n");
        DEL_IF_GET_EQUALS = new RedisScriptImpl<>(sb.toString(), Boolean.class);
    public RedisLock(StringRedisTemplate stringRedisTemplate, String lockKey) {
        this.stringRedisTemplate = stringRedisTemplate;
        this.lockKey = lockKey;
        this.lockValue = UUID.randomUUID().toString() + "." + System.currentTimeMillis();
    private boolean doTryLock(int lockSeconds) {
        if (locked) {
            throw new IllegalStateException("already locked!");
        }
        locked = stringRedisTemplate.execute(SETNX_AND_EXPIRE_SCRIPT, Collections.singletonList(lockKey), lockValue,
                String.valueOf(lockSeconds));
        return locked;
     * 尝试获得锁，成功返回true，如果失败立即返回false
     *
     * @param lockSeconds 加锁的时间(秒)，超过这个时间后锁会自动释放
    public boolean tryLock(int lockSeconds) {
        try {
            return doTryLock(lockSeconds);
        } catch (Exception e) {
            logger.error("tryLock Error", e);
            return false;
     * 轮询的方式去获得锁，成功返回true，超过轮询次数或异常返回false
     * @param lockSeconds       加锁的时间(秒)，超过这个时间后锁会自动释放
     * @param tryIntervalMillis 轮询的时间间隔(毫秒)
     * @param maxTryCount       最大的轮询次数
    public boolean tryLock(final int lockSeconds, final long tryIntervalMillis, final int maxTryCount) {
        int tryCount = 0;
        while (true) {
            if (++tryCount >= maxTryCount) {
                // 获取锁超时
                return false;
            }
            try {
                if (doTryLock(lockSeconds)) {
                    return true;
                }
            } catch (Exception e) {
                logger.error("tryLock Error", e);
                Thread.sleep(tryIntervalMillis);
            } catch (InterruptedException e) {
                logger.error("tryLock interrupted", e);
     * 解锁操作
    public void unlock() {
        if (!locked) {
            throw new IllegalStateException("not locked yet!");
        locked = false;
        // 忽略结果
        stringRedisTemplate.execute(DEL_IF_GET_EQUALS, Collections.singletonList(lockKey), lockValue);
    private static class RedisScriptImpl<T> implements RedisScript<T> {
        private final String script;
        private final String sha1;
        private final Class<T> resultType;
        public RedisScriptImpl(String script, Class<T> resultType) {
            this.script = script;
            this.sha1 = DigestUtils.sha1DigestAsHex(script);
            this.resultType = resultType;
        @Override
        public String getSha1() {
            return sha1;
        public Class<T> getResultType() {
            return resultType;
        public String getScriptAsString() {
            return script;
}

2. Implementation of Redis Lua counter by using lock for reference

(1) Tool class​​​

package han.zhang.utils;
 
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.core.script.DigestUtils;
import org.springframework.data.redis.core.script.RedisScript;
import java.util.Collections;
public class CountUtil {
    private static final LogUtils logger = LogUtils.getLogger(CountUtil.class);
    private final StringRedisTemplate stringRedisTemplate;
    /**
     * 使用脚本在redis服务器执行这个逻辑可以在一定程度上保证此操作的原子性
     * （即不会发生客户端在执行setNX和expire命令之间，发生崩溃或失去与服务器的连接导致expire没有得到执行，发生永久死计数器）
     * <p>
     * 除非脚本在redis服务器执行时redis服务器发生崩溃，不过此种情况计数器也会失效
     */
    private static final RedisScript<Boolean> SET_AND_EXPIRE_SCRIPT;
    static {
        StringBuilder sb = new StringBuilder();
        sb.append("local visitTimes = redis.call(&#39;incr&#39;, KEYS[1])\n");
        sb.append("if (visitTimes == 1) then\n");
        sb.append("\tredis.call(&#39;expire&#39;, KEYS[1], tonumber(ARGV[1]))\n");
        sb.append("\treturn false\n");
        sb.append("elseif(visitTimes > tonumber(ARGV[2])) then\n");
        sb.append("\treturn true\n");
        sb.append("else\n");
        sb.append("end");
        SET_AND_EXPIRE_SCRIPT = new RedisScriptImpl<>(sb.toString(), Boolean.class);
    }
    public CountUtil(StringRedisTemplate stringRedisTemplate) {
        this.stringRedisTemplate = stringRedisTemplate;
    public boolean isOverMaxVisitTimes(String key, int seconds, int maxTimes) throws Exception {
        try {
            return stringRedisTemplate.execute(SET_AND_EXPIRE_SCRIPT, Collections.singletonList(key), String.valueOf(seconds), String.valueOf(maxTimes));
        } catch (Exception e) {
            logger.error("RedisBusiness>>>isOverMaxVisitTimes; get visit times Exception; key:" + key + "result:" + e.getMessage());
            throw new Exception("already Over MaxVisitTimes");
        }
    private static class RedisScriptImpl<T> implements RedisScript<T> {
        private final String script;
        private final String sha1;
        private final Class<T> resultType;
        public RedisScriptImpl(String script, Class<T> resultType) {
            this.script = script;
            this.sha1 = DigestUtils.sha1DigestAsHex(script);
            this.resultType = resultType;
        @Override
        public String getSha1() {
            return sha1;
        public Class<T> getResultType() {
            return resultType;
        public String getScriptAsString() {
            return script;
}

(2) Call test code

 public void run(String... strings) {
        CountUtil countUtil = new CountUtil(SpringUtils.getStringRedisTemplate());
        try {
            for (int i = 0; i < 10; i++) {
                boolean overMax = countUtil.isOverMaxVisitTimes("zhanghantest", 600, 2);
                if (overMax) {
                    System.out.println("超过i:" + i + ":" + overMax);
                } else {
                    System.out.println("没超过i:" + i + ":" + overMax);
                }
            }
        } catch (Exception e) {
            logger.error("Exception {}", e.getMessage());
        }
    }

(3) Test result

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