要弄清楚分布式锁，先来了解什么是分布式锁？
同一个进程内的锁: 让线程按照指定的顺序去执行方法或者代码块，保证线程原子的进行
不同进程: jvm层面的锁就不管用了，那么可以利用第三方的一个组件，来获取锁，未获取到锁，则阻塞当前想要运行的线程。
场景1:
A: 银行存款200
读取到200，存入100，得到 200+100=300
B: 同一账号
读取到200，取出100，得到 200-100 = 100
最终账号里面应该是200不变，A得到300，B得到200，A-B 数据都出现不一致
所以我们可以使用分布式锁，让A，B两个进程顺序进行，这样B读取账号的时候就读到300，然后顺序进行最终数据是一致的。
场景2：
现在任务池里面有一堆任务，A，B都需要从任务池里面获取任务，当获取到任务的时候，把获取的任务从任务池里面删除，如果不作同步处理，那么A,B就可能获取到同一个任务
我们可以使用分布式锁，保证获取任务顺序进行。
为什么zk能实现分布式锁
Zookeeper是什么？
其实zookeeper可以理解为一个类似liunx的文件结构，里面的核心数据结构是node节点，然后可以存放少量数据。
如下图:
zk的node节点有四种属性
| node创建模式 | 中文解释 | 说明 |
|---|---|---|
| PERSISTENT | 持久节点 | znode不会自动删除，即使客户端断开连接 |
| PERSISTENT_SEQUENTIAL | 持久顺序节点 | znode不会自动删除，并且名字会自动递增 |
| EPHEMERAL | 临时节点 | znode自动删除，在客户端断开连接 |
| EPHEMERAL_SEQUENTIAL | 临时有序节点 | znode自动删除，并且名字会自动递增 |
可见zk的node特性，当我们创建节点的时候，可以指定创建模式，当指定EPHEMERAL_SEQUENTIAL的节点，会生成一个有序的节点，当我们获取锁的时候，可以判断，当前节点是否为最小节点，如果是，那么就认为获取锁成功，如果不是，那么我们监听比当前节点的前一个节点，当前一个节点放弃锁的时候，zk通过watcher机制，会通知客户端，这样当前节点就可以顺利获取锁了。当解锁的时候，delete掉当前节点就好了。
如何利用zk实现分布式锁
前面的理论知识，那么我们就可以用代码实现
package com.skrein.zk;
import lombok.extern.slf4j.Slf4j;
import org.I0Itec.zkclient.IZkDataListener;
import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.serialize.SerializableSerializer;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
/**
* @Author: hujiansong
* @Date: 2019/5/16 17:29
* @since: 1.8
*/
@Slf4j
public class DistributedLock implements Lock {
private static final String LOCK_PATH = "/LOCK";
private static final String ZOOKEEPER_IP_PORT = "localhost:2181";
private ZkClient client = new ZkClient(ZOOKEEPER_IP_PORT, 4000, 4000, new SerializableSerializer());
private String currentPath;
private String lastPath;
private CountDownLatch countDownLatch;
public DistributedLock() {
// 新建锁的时候，判断父节点是否存在
if (!client.exists(LOCK_PATH)) {
client.createPersistent(LOCK_PATH);
}
}
public void lock() {
if (!tryLock()) {
waitForLock();
lock();
} else {
log.info("获取锁成功,当前锁节点{}", currentPath);
}
}
private void waitForLock() {
// 监听lastPath
IZkDataListener listener = new IZkDataListener() {
public void handleDataChange(String s, Object o) throws Exception {
}
public void handleDataDeleted(String s) throws Exception {
log.info("前置节点已经删除,path={}", s);
if(countDownLatch!=null){
// 前置节点删除，通知唤醒去获取锁
countDownLatch.countDown();
}
}
};
// 监听前置节点
client.subscribeDataChanges(lastPath, listener);
// 判断前置节点是否存在
if (this.client.exists(lastPath)) {
countDownLatch = new CountDownLatch(1);
try {
// 前置节点存在，那么就阻塞等待
countDownLatch.await();
} catch (InterruptedException e) {
log.error("CountDownLatch await Exception", e);
}
}
// 前一个节点的listener解绑，因为已经删除完了
client.unsubscribeDataChanges(lastPath, listener);
}
public void lockInterruptibly() throws InterruptedException {
}
public boolean tryLock() {
// 先创建一个临时有序节点
if (currentPath == null) {
currentPath = client.createEphemeralSequential(LOCK_PATH + "/", "lock");
log.info("当前锁路径{}", currentPath);
}
// 获取所有子节点
List<String> children = client.getChildren(LOCK_PATH);
Collections.sort(children);
// 当前最小就认为获取锁成功，直接返回true
if (currentPath.equals(LOCK_PATH + "/" + children.get(0))) {
return true;
}
// 如果第一个不是,那么拿到currentPath 前一个 path
int i = Collections.binarySearch(children, currentPath.substring(6));
try {
lastPath = LOCK_PATH + "/" + children.get(i - 1);
} catch (Exception e) {
System.out.println(currentPath + "" + children);
}
return false;
}
public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
return false;
}
public void unlock() {
// 删除当前节点
log.info("释放锁{}",currentPath);
this.client.delete(currentPath);
}
public Condition newCondition() {
return null;
}
}
分布式锁使用
package com.skrein.zk;
import lombok.extern.slf4j.Slf4j;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
/**
* @Author: hujiansong
* @Date: 2019/5/16 17:53
* @since: 1.8
*/
@Slf4j
public class OrderService implements Runnable {
private static AtomicLong ATOMICLONG = new AtomicLong(1);
private static CountDownLatch COUNTDOWNLATCH = new CountDownLatch(10);
private Lock lock = new DistributedLock();
public void run() {
try {
COUNTDOWNLATCH.await();
} catch (InterruptedException e) {
log.error("CountDownLatch error", e);
}
String orderCode = null;
lock.lock();
try {
// do biz
orderCode = getOrderCode();
} finally {
lock.unlock();
}
}
public String getOrderCode() {
Date now = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmss");
return sdf.format(now) + ATOMICLONG.getAndIncrement();
}
public static void main(String[] args) {
for (int i = 1; i <= 10; i++) {
// 按照线程数迭代实例化线程
new Thread(new OrderService()).start();
// 创建一个线程，倒计数器减1
COUNTDOWNLATCH.countDown();
}
}
}
日志打印:
2019-05-17 10:53:14,542 INFO Thread-1 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000150
2019-05-17 10:53:14,542 INFO Thread-3 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000153
2019-05-17 10:53:14,542 INFO Thread-5 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000151
2019-05-17 10:53:14,543 INFO Thread-9 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000159
2019-05-17 10:53:14,543 INFO Thread-15 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000154
2019-05-17 10:53:14,543 INFO Thread-13 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000156
2019-05-17 10:53:14,543 INFO Thread-7 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000155
2019-05-17 10:53:14,544 INFO Thread-17 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000157
2019-05-17 10:53:14,543 INFO Thread-11 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000152
2019-05-17 10:53:14,544 INFO Thread-19 (com.skrein.zk.DistributedLock.tryLock:87) - 当前锁路径/LOCK/0000000158
2019-05-17 10:53:14,547 INFO Thread-1 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000150
2019-05-17 10:53:14,560 INFO Thread-1 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000150
2019-05-17 10:53:14,609 INFO Thread-5 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000151
2019-05-17 10:53:14,609 INFO Thread-5 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000151
2019-05-17 10:53:14,643 INFO Thread-11 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000152
2019-05-17 10:53:14,644 INFO Thread-11 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000152
2019-05-17 10:53:14,673 INFO Thread-3 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000153
2019-05-17 10:53:14,673 INFO Thread-3 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000153
2019-05-17 10:53:14,724 INFO Thread-15 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000154
2019-05-17 10:53:14,724 INFO Thread-15 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000154
2019-05-17 10:53:14,759 INFO Thread-7 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000155
2019-05-17 10:53:14,759 INFO Thread-7 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000155
2019-05-17 10:53:14,800 INFO Thread-13 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000156
2019-05-17 10:53:14,800 INFO Thread-13 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000156
2019-05-17 10:53:14,833 INFO Thread-17 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000157
2019-05-17 10:53:14,833 INFO Thread-17 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000157
2019-05-17 10:53:14,872 INFO Thread-19 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000158
2019-05-17 10:53:14,872 INFO Thread-19 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000158
2019-05-17 10:53:14,906 INFO Thread-9 (com.skrein.zk.DistributedLock.lock:46) - 获取锁成功,当前锁节点/LOCK/0000000159
2019-05-17 10:53:14,906 INFO Thread-9 (com.skrein.zk.DistributedLock.unlock:111) - 释放锁/LOCK/0000000159
可以看到10个线程，依次获取锁，解绑锁。
为什么Redis能实现分布式锁
Redis的SetNx命令当key存在的时候,返回null
为了保证锁的可用性，也就是当一个获取锁的线程挂掉了，后续线程也能正确的获取锁，那么需要利用key的expired属性来保证
因为是分布式锁，所以需要一个requestId来保障是哪个请求获取的锁，所以value可以是标识客户端的id
所以思路是：获取锁的时候通过sexNx来尝试获取锁，如果设置成功,那么获取锁成功，如果设置失败，那么需要轮询该key是否存在或者ttl(time to live)该key的存活时间，来重新去获取锁，直到获取锁成功。
解锁过程：get(key) == requestId ? del(key)
先判断key返回的结果是否是当前客户端，如果是，那么删除该key
相信处理过高并发的同学，一定能发现问题，这个操作并不是原子性的。也就是说有可能执行完get(key) == requestId,由于当前线程执行业务时间过长，超过了该key的过期时间锁已经废弃掉了，其他线程就获取了锁，然后接下来执行del(key)，就会把其他线程的锁给删除掉。
好在Redis给我们提供了lua脚本，可以将多个操作合并为一个原子操作。所以解锁操作使用lua脚本的方式进行。
Redis实现分布式锁过程
@Slf4j
public class RedisDistributedLock {
private Jedis client = new Jedis("localhost");
private static final String REDIS_LOCK_KEY = "DISTRIBUTE::LOCK::";
/**
* 锁的过期时间 ms
*/
private static final Long LOCK_EXPIRED_TIME = 60 * 1000L;
/**
* 请求锁的id，标识是哪个客户端获取的锁
*/
private String reqLockId;
public RedisDistributedLock() {
// 使用 uuid + 当前时间戳 来生成锁的ID
this.reqLockId = UUID.randomUUID().toString() + System.currentTimeMillis();
}
public void lock(String key) throws InterruptedException {
if (!tryLock(key)) {
waitForLock(key);
lock(key);
} else {
log.info("获取锁成功!");
}
}
private void waitForLock(final String key) throws InterruptedException {
// 开启一个线程去轮询redis的key过期时间
for (; ; ) {
String lockKey = REDIS_LOCK_KEY + key;
Long ttl = client.ttl(lockKey);
// key不存在或者已经过期，然后break掉重新去获取锁
if (!client.exists(lockKey) || ttl.intValue() <= 0) {
log.info("当前锁已经过期过期时间为:{}", ttl);
break;
}
}
}
// 获取锁操作很简单，直接setnx操作即可
public boolean tryLock(String key) {
String tryLock = client.set(REDIS_LOCK_KEY + key, reqLockId, SetParams.setParams().nx().px(LOCK_EXPIRED_TIME));
return tryLock != null && tryLock.equals("OK");
}
// 解锁采用eval lua脚本方式执行
public boolean unlock(String key) {
// 判断key的value是否为RequestId,如果是，那么删除key
String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
Object eval = client.eval(script, Collections.singletonList(REDIS_LOCK_KEY + key), Collections.singletonList(reqLockId));
return "OK".equals(eval);
}
public static void main(String[] args) throws InterruptedException {
String orderId = "123";
for (int i = 0; i < 10; i++) {
// 开启10个线程模拟并发
new Thread(new OrderService(orderId)).start();
}
}
static class OrderService implements Runnable {
private String orderId;
private RedisDistributedLock lock = new RedisDistributedLock();
public OrderService(String orderId) {
this.orderId = orderId;
}
public void run() {
try {
lock.lock(orderId);
log.info("do biz....");
Thread.sleep(5000);
log.info("do biz finished!");
} catch (InterruptedException e) {
log.error("lock InterruptedException", e);
} finally {
lock.unlock(orderId);
}
}
}
}
"C:\Program Files\Java\jdk1.8.0_161\bin\java.exe" -javaagent:C:\Users\hujiansong\AppData\Local\JetBrains\Toolbox\apps\IDEA-U\ch-0\191.7141.44\lib\idea_rt.jar=63968:C:\Users\hujiansong\AppData\Local\JetBrains\Toolbox\apps\IDEA-U\ch-0\191.7141.44\bin -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_161\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\rt.jar;C:\Users\hujiansong\Desktop\tmp\distributed-lock\target\classes;F:\DevTool\apache-maven-3.5.3\repo\org\projectlombok\lombok\1.18.6\lombok-1.18.6.jar;F:\DevTool\apache-maven-3.5.3\repo\org\slf4j\slf4j-api\1.7.26\slf4j-api-1.7.26.jar;F:\DevTool\apache-maven-3.5.3\repo\log4j\log4j\1.2.17\log4j-1.2.17.jar;F:\DevTool\apache-maven-3.5.3\repo\com\101tec\zkclient\0.10\zkclient-0.10.jar;F:\DevTool\apache-maven-3.5.3\repo\org\apache\zookeeper\zookeeper\3.4.8\zookeeper-3.4.8.jar;F:\DevTool\apache-maven-3.5.3\repo\org\slf4j\slf4j-log4j12\1.6.1\slf4j-log4j12-1.6.1.jar;F:\DevTool\apache-maven-3.5.3\repo\jline\jline\0.9.94\jline-0.9.94.jar;F:\DevTool\apache-maven-3.5.3\repo\io\netty\netty\3.7.0.Final\netty-3.7.0.Final.jar;F:\DevTool\apache-maven-3.5.3\repo\redis\clients\jedis\3.0.1\jedis-3.0.1.jar;F:\DevTool\apache-maven-3.5.3\repo\org\apache\commons\commons-pool2\2.4.3\commons-pool2-2.4.3.jar" com.skrein.redis.RedisDistributedLock
2019-05-17 17:11:14,007 INFO Thread-7 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:14,008 INFO Thread-7 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:19,009 INFO Thread-7 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:19,012 INFO Thread-8 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:19,012 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:19,013 INFO Thread-8 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:19,014 INFO Thread-8 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:19,012 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:19,012 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:19,012 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:19,012 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:19,012 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:19,012 INFO Thread-1 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:19,012 INFO Thread-6 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:24,014 INFO Thread-8 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:24,015 INFO Thread-6 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:24,016 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:24,016 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:24,017 INFO Thread-6 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:24,017 INFO Thread-6 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:24,016 INFO Thread-1 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:24,016 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:24,016 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:24,015 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:24,017 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:29,017 INFO Thread-6 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:29,017 INFO Thread-1 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:29,018 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:29,017 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:29,018 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:29,017 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:29,018 INFO Thread-1 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:29,018 INFO Thread-1 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:29,018 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:29,018 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:34,018 INFO Thread-1 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:34,019 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:34,019 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:34,019 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:34,020 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:34,020 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:34,020 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:34,020 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:34,020 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:39,020 INFO Thread-4 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:39,020 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:39,020 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:39,021 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:39,021 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:39,021 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:39,020 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:39,021 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:44,021 INFO Thread-9 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:44,021 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:44,021 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:44,022 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:44,022 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:44,022 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:44,022 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:49,022 INFO Thread-3 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:49,023 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:49,023 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:49,023 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:49,023 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:49,023 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:54,023 INFO Thread-0 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:54,024 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:54,024 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:55
2019-05-17 17:11:54,024 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:54,024 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:11:59,024 INFO Thread-5 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
2019-05-17 17:11:59,025 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.waitForLock:56) - 当前锁已经过期过期时间为:-2
2019-05-17 17:11:59,026 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.lock:45) - 获取锁成功!
2019-05-17 17:11:59,026 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.run:96) - do biz....
2019-05-17 17:12:04,026 INFO Thread-2 (com.skrein.redis.RedisDistributedLock.run:98) - do biz finished!
Process finished with exit code 0
可以看到锁依次进行获取，然后释放。
总结
ZK 实现分布式锁，主要利用zk的node创建模式以及通知机制。
Redis实现分布式，依赖SexNX命令，和解锁的lua脚本保证原子性
锁的可靠性主要包含如下4点：
| 可靠性特征 | 解释 |
|---|---|
| 锁是互斥 | 相同的时间，只有一个客户端可以获取到锁 |
| NO死锁 | 当客户端获取到锁，当客户端突然挂掉，接下来的客户端也能正确获取到锁 |
| 容错性 | Redis要保证可靠，即当Redis集群大多数节点可用的时候，锁也是可用的 |
| 正确释放锁 | A客户端不会释放掉B客户端的锁，锁要被加锁的人释放 |
下面就来聊聊zk和Redis对可靠性的满足:
| --- | ZK | Redis |
|---|---|---|
| 锁是互斥 | 满足，node唯一 | 满足，setNx |
| NO死锁 | 满足 session timeout机制 | 满足，expired |
| 容错性 | 依靠zk集群 | 依靠Redis集群 |
| 正确释放锁 | 依赖wather机制 | 轮询，靠代码实现 |
声明：以上是我学习分布式锁的demo例子，没有上过生产。如果上生产，任何问题概不负责。
代码仓库
完整代码放入了我的github仓库，欢迎star
代码地址如下：
