Redis实现分布式读写锁（Java基于Lua实现）
Redis实现分布式读写锁
前言
使用Jedis构建redis连接池，使用lua脚本命令保证redis的事务，以实现分布式的读写锁。项目中需要用到分布式的读写锁，开始使用Redisson的读写锁实现，压测的时候时不时会抛异常获取锁超时，初步判断是Redisson中redis连接池设置的太小。由于项目中还自己另外维护着一个redis的连接池JedisPool，故决定自己来实现分布式的可重入读写锁。
设计思路
目标：读锁可以被多个线程获取，同一个线程可以重入读锁，如果获取读锁的时候存在写锁，则需要等待写锁被释放才能获取；写锁的获取的时候，若存在读锁，则需要等待所有的读锁释放之后才能被获取，如果有线程正在获取写锁，其他获取读锁的线程将等待写锁被获取并释放之后才能获取读锁，写锁只能被一个线程持有，可以重入。
方案：
假设我们要操作“abc”这个读写锁
- 一个读锁在redis中的存在形式为一个hash结构，key为read_lock_abc，值为键值对组成的hash，键值对的键为thread_id(这个id由连接池id+获取锁的线程id，来区分分布式中的不同线程)，值为该线程重入读锁的次数。
- 一个写锁分为两部分，一个是key为write_lock_abc，值为thread_id（同上）；另外一个key为reentrant_write_lock_abc,值为被重入的次数。
实现
RedisReadWriteLock.java 该类用于维护读写锁的单例
public class RedisReadWriteLock {
//读锁
private static volatile RedisReadLock redisReadLock;
//写锁
private static volatile RedisWriteLock redisWriteLock;
//双重检查锁实现单例
public static RedisReadLock readLock(){
if(redisReadLock == null){
synchronized (RedisReadLock.class){
if (redisReadLock == null){
redisReadLock = new RedisReadLock();
}
}
}
return redisReadLock;
}
public static RedisWriteLock writeLock(){
if(redisWriteLock == null){
synchronized (RedisWriteLock.class){
if (redisWriteLock == null){
redisWriteLock = new RedisWriteLock();
}
}
}
return redisWriteLock;
}
// 构建锁的key
public static String getReadLockKey(String name){
return RedisLockConf.READ_LOCK_PREFIX + name;
}
public static String getWriteLockKey(String name){
return RedisLockConf.WRITE_LOCK_PREFIX + name;
}
public static String getReentrantWriteLockKey(String name){
return RedisLockConf.REENTRANT_WRITE_LOCK_PREFIX + name;
}
//由连接池id+获取锁的线程id，来区分分布式中的不同线程
public static String getThreadUid(){
return JedisConnectPoll.JEDIS_CONNECT_POLL_UUID.toString() + ":" + Thread.currentThread().getId();
}
}
public class RedisLockConf {
public static final String READ_LOCK_PREFIX = "read_lock_";
public static final String WRITE_LOCK_PREFIX = "write_lock_";
public static final String REENTRANT_WRITE_LOCK_PREFIX = "reentrant_write_lock_";
}
RedisReadLock.java 读锁的实现
@Slf4j
public class RedisReadLock {
public void lock(String name){
tryLock(name, Long.MAX_VALUE, 30, TimeUnit.SECONDS);
}
public void lock(String name, long leaseTime, TimeUnit unit){
tryLock(name, Long.MAX_VALUE, leaseTime, unit);
}
public boolean tryLock(String name, long waitTime, long leaseTime, TimeUnit unit){
Long waitUntilTime = unit.toMillis(waitTime) + System.currentTimeMillis();
if(waitUntilTime < 0){
waitUntilTime = Long.MAX_VALUE;
}
Long leastTimeLong = unit.toMillis(leaseTime);
StringBuilder sctipt = new StringBuilder();
// write-lock read-lock uuid leaseTime，后面会专门说这段脚本
sctipt.append("if not redis.call('GET',KEYS[1]) then ")
//redis.call('GET',KEYS[1])之类的命令，若没有值返回的布尔类型的false，不是nil
.append("local count = redis.call('HGET',KEYS[2],KEYS[3]);")
.append("if count then ")
.append("count = tonumber(count) + 1;")
.append("redis.call('HSET',KEYS[2],KEYS[3],count);")
.append("else ")
.append("redis.call('HSET',KEYS[2],KEYS[3],1);")
.append("end;")
.append("local t = redis.call('PTTL', KEYS[2]);")
.append("redis.call('PEXPIRE', KEYS[2], math.max(t, ARGV[1]));")
.append("return 1;")
.append("else ")
.append("return 0;")
.append("end;");
for(;;){
if(System.currentTimeMillis() > waitUntilTime){
return false;
}
Long res = (Long) JedisTemplate.operate().eval(sctipt.toString(), 3, RedisReadWriteLock.getWriteLockKey(name), RedisReadWriteLock.getReadLockKey(name), RedisReadWriteLock.getThreadUid(), leastTimeLong.toString());
if(res.equals(1L)){
//successGetReadLock
log.debug("success get read lock, readLock={}", RedisReadWriteLock.getReadLockKey(name));
break;
}else {
//need to wait write lock to be released
log.debug("wait write lock release, writeLock={}", RedisReadWriteLock.getWriteLockKey(name));
try {
TimeUnit.MILLISECONDS.sleep(50);
} catch (InterruptedException e) {
log.error("wait write lock release exception", e);
}
}
}
return true;
}
public void unlock(String name){
StringBuilder sctipt = new StringBuilder();
sctipt.append("local count = redis.call('HGET',KEYS[1],KEYS[2]);")
.append("if count then ")
.append("if (tonumber(count) > 1) then ")
.append("count = tonumber(count) - 1;")
.append("redis.call('HSET',KEYS[1],KEYS[2],count);")
.append("else ")
.append("redis.call('HDEL',KEYS[1],KEYS[2]);")
.append("end;")
.append("end;")
.append("return;");
JedisTemplate.operate().eval(sctipt.toString(), 2, RedisReadWriteLock.getReadLockKey(name), RedisReadWriteLock.getThreadUid());
log.debug("success unlock read lock, readLock={}", RedisReadWriteLock.getReadLockKey(name));
}
}
redis执行lua脚本的命令格式为：EVAL script numkeys key [key …] arg [arg …]
redis 127.0.0.1:6379> EVAL "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 2 key1 key2 first second
1) "key1"
2) "key2"
3) "first"
4) "second"
-- 读锁获取的lua脚本
-- 判断不存在写锁
if not redis.call('GET',KEYS[1]) then
local count = redis.call('HGET',KEYS[2],KEYS[3])
-- 如果该线程已经获取了该读锁，就重入，重入次数加1
if count then
count = tonumber(count) + 1
redis.call('HSET',KEYS[2],KEYS[3],count)
else
redis.call('HSET',KEYS[2],KEYS[3],1)
end
-- 检查之前读锁的过期时间，和当前加的读锁的过期时间做对比，更新过期时间
local t = redis.call('PTTL', KEYS[2])
redis.call('PEXPIRE', KEYS[2], math.max(t, ARGV[1]))
return 1
else
-- 若存在写锁，返回获取失败，外层的代码做轮询尝试加锁
return 0
end;
-- 读锁释放的lua脚本
-- 获取锁被当前线程重入的次数
local count = redis.call('HGET',KEYS[1],KEYS[2])
if count then
if (tonumber(count) > 1) then
count = tonumber(count) - 1
redis.call('HSET',KEYS[1],KEYS[2],count)
else
redis.call('HDEL',KEYS[1],KEYS[2])
end
end
return
RedisWriteLock.java 写锁的实现
@Slf4j
public class RedisWriteLock {
public void lock(String name){
tryLock(name, Long.MAX_VALUE, 30, TimeUnit.SECONDS);
}
public void lock(String name, long leaseTime, TimeUnit unit){
tryLock(name, Long.MAX_VALUE, leaseTime, unit);
}
public boolean tryLock(String name, long waitTime, long leaseTime, TimeUnit unit){
Long waitUntilTime = unit.toMillis(waitTime) + System.currentTimeMillis();
if(waitUntilTime < 0){
waitUntilTime = Long.MAX_VALUE;
}
Long leastTimeLong = unit.toMillis(leaseTime);
StringBuilder sctipt = new StringBuilder();
// write-lock reentrant-write-lock uuid leaseTime
sctipt.append("if redis.call('SET',KEYS[1],ARGV[1],'NX','PX',ARGV[2]) then ")
.append("redis.call('SET',KEYS[2],1,'PX',ARGV[2]);")
.append("return 1;")
.append("else ")
.append("if (redis.call('GET',KEYS[1])== ARGV[1]) then ")
.append("local count = redis.call('GET',KEYS[2]);")
.append("if not count then ")
.append("redis.call('SET',KEYS[2],1,'PX',ARGV[2]);")
.append("return 1;")
.append("else ")
.append("count = tonumber(count) + 1;")
.append("redis.call('SET',KEYS[2],count,'PX',ARGV[2]);")
.append("return count;")
.append("end;")
.append("else ")
.append("return 0;")
.append("end;")
.append("end;");
for(;;){
if(System.currentTimeMillis() > waitUntilTime){
return false;
}
Long res = (Long) JedisTemplate.operate().eval(sctipt.toString(), 2, RedisReadWriteLock.getWriteLockKey(name), RedisReadWriteLock.getReentrantWriteLockKey(name), RedisReadWriteLock.getThreadUid(), leastTimeLong.toString());
if(res.equals(1L)){
//successGetWriteLock
log.debug("success get write lock, writeLock = {}", RedisReadWriteLock.getWriteLockKey(name));
for(;;){
if(JedisTemplate.operate().exists(RedisReadWriteLock.getReadLockKey(name))){
log.debug("wait read lock release, readLock = {}", RedisReadWriteLock.getReadLockKey(name));
try {
TimeUnit.MILLISECONDS.sleep(100);
} catch (InterruptedException e) {
log.error("wait read lock release exception", e);
}
}else{
break;
}
}
break;
}else if(res.equals(0L)){
//need to wait write lock to be released
log.debug("wait write lock release, writeLock = {}", RedisReadWriteLock.getWriteLockKey(name));
try {
TimeUnit.MILLISECONDS.sleep(100);
} catch (InterruptedException e) {
log.error("wait write lock release exception", e);
}
}else{
log.debug("success in reentrant write lock, reentrantWriteLock = {}, count now = {}", RedisReadWriteLock.getReentrantWriteLockKey(name), res);
break;
}
}
return true;
}
public void unlock(String name){
StringBuilder sctipt = new StringBuilder();
//write-lock reentrant-write-lock uuid
sctipt.append("if (redis.call('GET',KEYS[1])== ARGV[1]) then ")
.append("local count = redis.call('GET',KEYS[2]);")
.append("if count then ")
.append("if (tonumber(count) > 1) then ")
.append("count = tonumber(count) - 1;")
.append("local live = redis.call('PTTL',KEYS[2]);")
.append("redis.call('SET',KEYS[2],count,'PX',live);")
//success unlock reentrant-write-lock
.append("return count;")
.append("else ")
.append("redis.call('DEL',KEYS[2]);")
.append("redis.call('DEL',KEYS[1]);")
//success unlock
.append("return 0;")
.append("end;")
.append("else ")
.append("redis.call('DEL',KEYS[1]);")
.append("return 0;")
.append("end;")
.append("else ")
//fail unlock, thread not get the lock
.append("return -1;")
.append("end;");
Long res = (Long) JedisTemplate.operate().eval(sctipt.toString(), 2, RedisReadWriteLock.getWriteLockKey(name), RedisReadWriteLock.getReentrantWriteLockKey(name), RedisReadWriteLock.getThreadUid());
if(res.equals(0L)){
log.debug("success unlock write lock, writeLock = {}", RedisReadWriteLock.getWriteLockKey(name));
}else if(res.equals(-1L)){
log.debug("fail unlock, thread not get the lock, writeLock = {}, thread = {}", RedisReadWriteLock.getReentrantWriteLockKey(name), RedisReadWriteLock.getThreadUid());
}else {
log.debug("success unlock reentrant write lock, reentrantWriteLock = {}, count left = {}", RedisReadWriteLock.getReentrantWriteLockKey(name), res);
}
}
}
-- 写锁获取的lua脚本
-- 没有写锁，则成功设置
if redis.call('SET',KEYS[1],ARGV[1],'NX','PX',ARGV[2]) then
-- 重入数记为1
redis.call('SET',KEYS[2],1,'PX',ARGV[2])
return 1
else
-- 写锁已经被获取，判断已经获取写锁的线程是不是当前线程
if (redis.call('GET',KEYS[1])== ARGV[1]) then
-- 若是当前线程，则重入数+1
local count = redis.call('GET',KEYS[2])
if not count then
redis.call('SET',KEYS[2],1,'PX',ARGV[2])
return 1;
else
count = tonumber(count) + 1;
redis.call('SET',KEYS[2],count,'PX',ARGV[2])
return count
end
else
return 0
end
end
-- 写锁释放的lua脚本
-- 判断是否是当前线程获取的写锁
if (redis.call('GET',KEYS[1])== ARGV[1]) then
-- 是当前线程获取的写锁，判断锁是否被重入，重入数减到1后释放锁
local count = redis.call('GET',KEYS[2])
if count then
if (tonumber(count) > 1) then
count = tonumber(count) - 1
local live = redis.call('PTTL',KEYS[2])
redis.call('SET',KEYS[2],count,'PX',live)
-- 返回该线程对该锁剩余的重入次数
return count
else
redis.call('DEL',KEYS[2])
redis.call('DEL',KEYS[1])
return 0
end
else
redis.call('DEL',KEYS[1])
return 0
end
else
-- 其他线程获取的该写锁，该线程解锁失败
return -1
end
测试如下：
public static void main(String[] args) {
final int[] num = {0};
for (int i = 0; i < 10 ; i++) {
Thread thread = new Thread(() -> {
RedisReadWriteLock.writeLock().tryLock("ccc", 30,300, TimeUnit.SECONDS);
num[0]++;
System.out.println("【写】：" + num[0]);
RedisReadWriteLock.writeLock().unlock("ccc");
});
thread.start();
}
for (int i = 0; i < 100 ; i++) {
Thread thread = new Thread(() -> {
RedisReadWriteLock.readLock().tryLock("ccc", 30,300, TimeUnit.SECONDS);
System.out.println("读：" + num[0]);
RedisReadWriteLock.readLock().unlock("ccc");
});
thread.start();
if(i % 3 == 0){
try {
TimeUnit.MILLISECONDS.sleep(50);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
运行结果
【写】：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
读：1
【写】：2
【写】：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
读：3
【写】：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
读：4
【写】：5
读：5
读：5
读：5
读：5
读：5
读：5
【写】：6
读：6
读：6
读：6
读：6
读：6
读：6
【写】：7
读：7
读：7
读：7
读：7
读：7
读：7
读：7
读：7
读：7
【写】：8
读：8
读：8
读：8
读：8
读：8
读：8
读：8
读：8
读：8
读：8
读：8
读：8
【写】：9
读：9
读：9
读：9
读：9
读：9
读：9
【写】：10
读：10
读：10
读：10
JedisTemplate其实是对从JedisPool获取的Jedis连接做的一个cglib的代理，用于使用完之后自动调用Jedis实例的close方法将连接归还到JedisPool。代理肯定会存在一点性能损耗，但是也简化了编码，以及避免了忘记归还连接，导致池的连接被耗空。
需要引入cglib的依赖
<dependency>
<groupId>cglibgroupId>
<artifactId>cglibartifactId>
<version>3.2.10version>
dependency>
public class JedisTemplate {
public static Jedis operate(){
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(Jedis.class);
enhancer.setCallback(new JedisCglibProxyIntercepter());
return (Jedis) enhancer.create();
}
}
public class JedisCglibProxyIntercepter implements MethodInterceptor {
@Override
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
//try后会自动调用jedis的close方法释放资源
try(Jedis jedis = JedisConnectPoll.getJedis()){
return method.invoke(jedis, objects);
}
}
}
JedisPool连接池的代码也贴一下：
需要添加下面的Jedis依赖
<dependency>
<groupId>redis.clientsgroupId>
<artifactId>jedisartifactId>
<version>3.0.1version>
dependency>
@Slf4j的注解是需要添加lombok依赖，然后还要对应的日志依赖，这个按个人需要选择吧
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<version>1.18.6version>
<scope>providedscope>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-apiartifactId>
<version>1.7.16version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>jcl-over-slf4jartifactId>
<version>1.7.16version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>log4j-over-slf4jartifactId>
<version>1.7.16version>
dependency>
<dependency>
<groupId>ch.qos.logbackgroupId>
<artifactId>logback-coreartifactId>
<version>1.1.6version>
dependency>
<dependency>
<groupId>ch.qos.logbackgroupId>
<artifactId>logback-classicartifactId>
<version>1.1.6version>
<exclusions>
<exclusion>
<artifactId>slf4j-apiartifactId>
<groupId>org.slf4jgroupId>
exclusion>
exclusions>
dependency>
@Slf4j
public class JedisConnectPoll {
public static final UUID JEDIS_CONNECT_POLL_UUID = UUID.randomUUID();
//连接redis实例的ip
private static final String REDIS_ADDRESS = "127.0.0.1";
//连接redis实例的端口
private static final int PORT = "6379";
//密码
private static final String PASSWORD = "";
//多线程环境中,连接实例的最大数,如果设为-1则无上线,建议设置,否则有可能导致资源耗尽
private static final int MAX_ACTIVE = 160;
//在多线程环境中,连接池中最大空闲连接数,单线程环境没有实际意义
private static final int MAX_OLDE = 128;
//在多线程环境中,连接池中最小空闲连接数
private static final int MIN_OLDE = 8;
//多长时间将空闲线程进行回收,单位毫秒
private static final int METM = 2000;
//对象空闲多久后逐出, 当空闲时间>该值 且 空闲连接>最大空闲数 时直接逐出,不再根据MinEvictableIdleTimeMillis判断 (默认逐出策略)
private static final int SMETM = 2000;
//逐出扫描的时间间隔(毫秒) 如果为负数,则不运行逐出线程, 默认-1,只有运行了此线程,MIN_OLDE METM/SMETM才会起作用
private static final int TBERM = 1000;
//当连接池中连接不够用时,等待可用连接的最大时间，单位毫秒，默认值为-1，表示永不超时。如果超过等待时间，则直接抛出JedisConnectionException；
private static final int MAX_WAIT = 1000;
//超时时间,单位毫秒
private static final int TIME_OUT = 10000;
//在借用一个jedis连接实例时，是否提前进行有效性确认操作；如果为true，则得到的jedis实例均是可用的；
private static final boolean TEST_ON_BORROW = false;
//连接池实例
private static JedisPool jedisPool = null;
static {
initPoll();
}
private static void initPoll() {
try {
JedisPoolConfig config = new JedisPoolConfig();
config.setMaxTotal(MAX_ACTIVE);
config.setMaxIdle(MAX_OLDE);
config.setMaxWaitMillis(MAX_WAIT);
config.setTestOnBorrow(TEST_ON_BORROW);
config.setMinIdle(MIN_OLDE);
config.setMinEvictableIdleTimeMillis(METM);
config.setSoftMinEvictableIdleTimeMillis(SMETM);
config.setTimeBetweenEvictionRunsMillis(TBERM);
if(!"".equals(PASSWORD)){
jedisPool = new JedisPool(config, REDIS_ADDRESS, PORT, TIME_OUT, PASSWORD);
}else {
jedisPool = new JedisPool(config, REDIS_ADDRESS, PORT, TIME_OUT);
}
} catch (Exception e) {
log.error("initial JedisPoll fail: {}",e);
}
}
public static Jedis getJedis(){
return jedisPool.getResource();
}
}