Redis被经常用来实现分布式锁，本文主要讲述redis如何实现一个分布式锁的demo。
获取锁
redis分布式锁的实现主要是通过redis的set命令实现：
SET key value nx PX milliseconds
nx : 当key存在的时候才将set对应的key，value写入到redis数据库里面。如果设置成功之后，就返回OK，已经存在就返回nil，当前set命令也是一个原子操作，可以作为分布式锁。px milliseconds: 为当前key设置过期时间，当时间过了之后会将当前key删除。主要是方式获取锁之后未正常释放，导致死锁，一直无法获取锁。超时时间需要合理设置，需要保证当前业务能够处理完。
private static final String LOCK_SUCCESS = "OK";
private static final Long UNLOCK_SUCCESS = 1L;
//
private static final String UNLOCK_SCRIPT = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
private final JedisCluster cluster;
private final long lockTimeout;
private final String lockKey;
public RedisDistributedLockImpl(JedisCluster cluster, String lockKey, long lockTimeout) {
this.cluster = cluster;
this.lockTimeout = lockTimeout;
this.lockKey = lockKey;
}
@Override
public String lock() {
long end = System.currentTimeMillis() + lockTimeout;
String requireToken = String.valueOf(System.currentTimeMillis());
int expireTime = 300 * 1000;
SetParams params = new SetParams().nx().px(expireTime);
while (System.currentTimeMillis() < end) {
try {
String result = cluster.set(lockKey, requireToken, params);
if (LOCK_SUCCESS.equals(result)) {
System.out.println("lock success");
return requireToken;
}
System.out.println("lock failed trying");
Thread.sleep(100);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
return requireToken;
}
释放锁
释放锁，主要是需要通过原子操作将锁对应的key删除，可以通过下面lua脚本删除。
if redis.call('get', KEYS[1]) == ARGV[1] then
return redis.call('del', KEYS[1])
else
return 0
end
释放锁的详细代码：
@Override
public boolean unlock(String identify) {
if (identify == null || identify.trim().length() == 0) {
return false;
}
Object obj = new Object();
try {
obj = cluster.eval(UNLOCK_SCRIPT, Collections.singletonList(lockKey), Collections.singletonList(identify));
if (UNLOCK_SUCCESS.equals(obj)) {
System.out.println("release lock success, requestToken:" + identify);
return true;
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("release lock failed, requestToken:" + identify + ", result:" + obj);
return false;
}
测试分布式锁
使用下面代码模拟秒杀场景：
public class RedisDistributedLockTest {
static int n = 500;
public static void secKill() {
System.out.println("商品数量：" + --n);
}
public static void main(String[] args) {
Runnable runnable = () -> {
RedisDistributedLockImpl lock = null;
String unLockIdentify = null;
try {
Set<HostAndPort> set = new HashSet<>();
set.add(new HostAndPort("127.0.0.1", 30001));
JedisPoolConfig config = new JedisPoolConfig();
JedisCluster cluster = new JedisCluster(set, config);
lock = new RedisDistributedLockImpl(cluster, "test1", 20000);
unLockIdentify = lock.lock();
System.out.println(Thread.currentThread().getName() + "正在运行");
secKill();
} finally {
if (lock != null) {
lock.unlock(unLockIdentify);
}
}
};
System.out.println("------------------开始--------------");
for (int i = 0; i < 100; i++) {
Thread t = new Thread(runnable);
t.start();
}
}
}
执行结果如下：
