一、前言
前段时间出去耍，没得时间写博客，最近没有什么系统性的文章，写一些实际工作中遇到的问题。我个人项目在公司服务器是部署到两台机子上，但是在消费资源的时候，出现数据同步问题。我们原来用的是class的实例做同步出来，这个实例对于单台机子拥有，对两台机子就失去作用了。这个时候就需要分布式锁实现同步处理。
二、redis 实现分布式锁
首先我想分享一点，当然在网上看的redis 的源码，自己没有仔细分析，redis 的同步是支持多进程多线程的，最后都是用文件来做同步，这样就摆脱单线程问题。既然它本身解决了分布式锁的问题，我们就可以用它来解决我们事物同步问题。对于redis不了解的同学不重要，毕竟只是一个数据库，你不是dba一样用mysql是不是？？
2.1 编写redis 锁
对于 redis锁的主要步骤如下，思路首先要清晰
- 首先初始化redis获取redis客户端jedis(或者SharedJedis)
- 制定锁定时间参数，锁等待与锁超时
- 编写锁方法
- 关闭锁
注：再次我们就要贴出代码了， 代理里面前面的都是构造方法，最后两个方法才是关键（申明:代码来自网络）
package com.github.jedis.lock;
import redis.clients.jedis.Jedis;
/**
* Redis distributed lock implementation.
*/
public class JedisLock {
Jedis jedis;
/**
* Lock key path.
*/
String lockKey;
/**
* Lock expiration in miliseconds.
* 锁超时，防止线程在入锁以后，无限的执行等待
*/
int expireMsecs = 60 * 1000;
/**
* Acquire timeout in miliseconds.
* 锁等待，防止线程饥饿
*/
int timeoutMsecs = 10 * 1000;
boolean locked = false;
/**
* Detailed constructor with default acquire timeout 10000 msecs and lock expiration of 60000 msecs.
*
* @param jedis
* @param lockKey lock key (ex. account:1, ...)
*/
public JedisLock(Jedis jedis, String lockKey) {
this.jedis = jedis;
this.lockKey = lockKey;
}
/**
* Detailed constructor with default lock expiration of 60000 msecs.
*
* @param jedis
* @param lockKey lock key (ex. account:1, ...)
* @param timeoutMsecs acquire timeout in miliseconds (default: 10000 msecs)
*/
public JedisLock(Jedis jedis, String lockKey, int timeoutMsecs) {
this(jedis, lockKey);
this.timeoutMsecs = timeoutMsecs;
}
/**
* Detailed constructor.
*
* @param jedis
* @param lockKey lock key (ex. account:1, ...)
* @param timeoutMsecs acquire timeout in miliseconds (default: 10000 msecs)
* @param expireMsecs lock expiration in miliseconds (default: 60000 msecs)
*/
public JedisLock(Jedis jedis, String lockKey, int timeoutMsecs, int expireMsecs) {
this(jedis, lockKey, timeoutMsecs);
this.expireMsecs = expireMsecs;
}
/**
* Detailed constructor with default acquire timeout 10000 msecs and lock expiration of 60000 msecs.
*
* @param lockKey lock key (ex. account:1, ...)
*/
public JedisLock(String lockKey) {
this(null, lockKey);
}
/**
* Detailed constructor with default lock expiration of 60000 msecs.
*
* @param lockKey lock key (ex. account:1, ...)
* @param timeoutMsecs acquire timeout in miliseconds (default: 10000 msecs)
*/
public JedisLock(String lockKey, int timeoutMsecs) {
this(null, lockKey, timeoutMsecs);
}
/**
* Detailed constructor.
*
* @param lockKey lock key (ex. account:1, ...)
* @param timeoutMsecs acquire timeout in miliseconds (default: 10000 msecs)
* @param expireMsecs lock expiration in miliseconds (default: 60000 msecs)
*/
public JedisLock(String lockKey, int timeoutMsecs, int expireMsecs) {
this(null, lockKey, timeoutMsecs, expireMsecs);
}
/**
* @return lock key
*/
public String getLockKey() {
return lockKey;
}
/**
* Acquire lock.
*
* @return true if lock is acquired, false acquire timeouted
* @throws InterruptedException in case of thread interruption
*/
public synchronized boolean acquire() throws InterruptedException {
return acquire(jedis);
}
/**
* Acquire lock.
*
* @param jedis
* @return true if lock is acquired, false acquire timeouted
* @throws InterruptedException in case of thread interruption
*/
public synchronized boolean acquire(Jedis jedis) throws InterruptedException {
//锁等待，防止线程饥饿
int timeout = timeoutMsecs;
while (timeout >= 0) {
//锁超时，防止线程在入锁以后，无限的执行等待(为什么加1:因为可能有相同时间的操作,这样做不完美,但是实用)
long expires = System.currentTimeMillis() + expireMsecs + 1;
String expiresStr = String.valueOf(expires); //锁到期时间
if (jedis.setnx(lockKey, expiresStr) == 1) {
// lock acquired
locked = true;
return true;
}
String currentValueStr = jedis.get(lockKey); //redis里的时间
if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
//判断是否为空，不为空的情况下，如果被其他线程设置了值，则第二个条件判断是过不去的
// lock is expired
String oldValueStr = jedis.getSet(lockKey, expiresStr);
//获取上一个锁到期时间，并设置现在的锁到期时间，
//只有一个线程才能获取上一个线上的设置时间，因为jedis.getSet是同步的
if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
//如过这个时候，多个线程恰好都到了这里，但是只有一个线程的设置值和当前值相同，他才有权利获取锁
// lock acquired
locked = true;
return true;
}
}
timeout -= 100;
Thread.sleep(100);
}
return false;
}
/**
* Acqurired lock release.
*/
public synchronized void release() {
release(jedis);
}
/**
* Acqurired lock release.
*/
public synchronized void release(Jedis jedis) {
if (locked) {
jedis.del(lockKey);
locked = false;
}
}
}
以上锁定原理：就是锁定一个键，时间为自己定义，为了防止其他操作修改值 特意判断如下
Long.parseLong(currentValueStr) < System.currentTimeMillis()保证了每次都是原来的值。
2.2 测试锁
package com.chinaso.phl.concurrent;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.apache.commons.pool2.impl.GenericObjectPoolConfig;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import com.github.jedis.lock.JedisLock;
/**
* @author come from network
kk @date 2014-3-1
*/
public class JedisLockTest {
private static ExecutorService executor = Executors.newFixedThreadPool(100);
/**
* @param args
* @author piaohailin
* @date 2014-3-1
*/
public static void main(String[] args) {
// final JedisPool pool = new JedisPool("192.168.56.2", 6379);
GenericObjectPoolConfig poolConfig = new GenericObjectPoolConfig();
final JedisPool pool = new JedisPool(poolConfig, "192.168.142.237", 6379, 3000); //最后一个参数为密码
final String key = "h";
for (int i = 0; i < 5; i++) {
executor.execute(new Runnable() {
@Override
public void run() {
try {
Jedis jedis = pool.getResource();
JedisLock lock = new JedisLock(jedis, key, 3000, 10000);
if (lock.acquire()) {
//如果锁上了
try {
Thread.sleep(1000);
System.out.println(System.currentTimeMillis());
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.release();//则解锁
}
}
} catch (Throwable t) {
t.printStackTrace();
}
}
});
}
}
}
测试结果：
1459417921818 1459417922871 1459417923922
2.2.1 观看不能锁的情况
package com.chinaso.phl.concurrent;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.apache.commons.pool2.impl.GenericObjectPoolConfig;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import com.github.jedis.lock.JedisLock;
/**
* @author come from network
kk @date 2014-3-1
*/
public class JedisLockTest {
private static ExecutorService executor = Executors.newFixedThreadPool(100);
/**
* @param args
* @author piaohailin
* @date 2014-3-1
*/
public static void main(String[] args) {
// final JedisPool pool = new JedisPool("192.168.56.2", 6379);
GenericObjectPoolConfig poolConfig = new GenericObjectPoolConfig();
final JedisPool pool = new JedisPool(poolConfig, "192.168.142.237", 6379, 3000); //最后一个参数为密码
final String key = "h";
for (int i = 0; i < 3; i++) {
executor.execute(new Runnable() {
@Override
public void run() {
try {
Jedis jedis = pool.getResource();
JedisLock lock = new JedisLock(jedis, key, 3000, 10000);
if (true) {
//如果锁上了
try {
Thread.sleep(1000);
System.out.println(System.currentTimeMillis());
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.release();//则解锁
}
}
} catch (Throwable t) {
t.printStackTrace();
}
}
});
}
}
}
测试结果
1459418004056 1459418004056 1459418004056
