redisService 分布锁

最新推荐文章于 2023-11-08 09:26:12 发布

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本文详细介绍了Redis分布式锁的实现原理与应用方法，包括加锁、解锁操作及超时处理，通过实例展示了如何利用Redis实现分布式场景下的锁机制。

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package com.sohu.redis;

import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import org.apache.log4j.Logger;

import redis.clients.jedis.Jedis;

import com.sohu.service.RedisService;

/**
* @author qiaowang
* @date 2014-4-11 下午3:49:21
*/
public class RedisLock {

private static final Logger log = Logger.getLogger(RedisTest.class);

//加锁标志
public static final String LOCKED = "TRUE";
public static final long ONE_MILLI_NANOS = 1000000L;
//默认超时时间（毫秒）
public static final long DEFAULT_TIME_OUT = 3000;
public static final Random r = new Random();
//锁的超时时间（秒），过期删除
public static final int EXPIRE = 5 * 60;

public static RedisService redisService;

static {
redisService = new RedisService();
}

//锁状态标志
private boolean success = false;

public boolean acquireLock(String lock) {
// 1. 通过SETNX试图获取一个lock
//boolean success = false;
Jedis jedis = redisService.getWClient();
long value = System.currentTimeMillis() + EXPIRE + 1;
//System.out.println(value);
long acquired = jedis.setnx(lock, String.valueOf(value));
//SETNX成功，则成功获取一个锁
System.out.println(acquired);
if (acquired == 1)
success = true;
//SETNX失败，说明锁仍然被其他对象保持，检查其是否已经超时
else {
long oldValue = Long.valueOf(jedis.get(lock));

//超时
if (oldValue < System.currentTimeMillis()) {
String getValue = jedis.getSet(lock, String.valueOf(value));
// 获取锁成功
if (Long.valueOf(getValue) == oldValue)
success = true;
// 已被其他进程捷足先登了
else
success = false;
}
//未超时，则直接返回失败
else
success = false;
}
redisService.returnWriteResource(jedis);
return success;
}

//释放锁
public void releaseLock(String lock) {
Jedis jedis = redisService.getWClient();
long current = System.currentTimeMillis();
// 避免删除非自己获取得到的锁
if (current < Long.valueOf(jedis.get(lock)))
jedis.del(lock);
redisService.returnWriteResource(jedis);
}

public static void main(String[] args) throws Exception {

Runnable task = new Runnable(){

@Override
public void run() {
String CACHE_LOCK_KEY = "focus-app-report:reloadpic:lock:key3";
RedisLock redisLock = new RedisLock();
try {
/**
* 首先获取分布锁，避免多个实例同时加载信息到缓存的问题
*/

boolean getLock = redisLock.acquireLock(CACHE_LOCK_KEY);
if (getLock) {
log.info("========开始从PHP接口加载数据==========");

System.out.println("return redis lock" );
System.out.println("do something" );
log.info("========从PHP接口加载数据完毕==========");
//
//Thread.sleep(3000);
}
} catch (Exception e) {
System.out.println("return redis fail" );
log.error("", e);
} finally {
try {
redisLock.releaseLock(CACHE_LOCK_KEY);
System.out.println("return redis unlock" );
} catch (Exception e) {
log.error("", e);
}
}

}

};

ExecutorService singleExecutor = Executors.newFixedThreadPool(10);
for (int i = 0; i < 10; i++) {
singleExecutor.execute(task);
}

singleExecutor.shutdown();
}

}