Zookeeper分布式锁
作者：互联网
1、分布式锁
在我们进行单机应用开发时，涉及到同步时，我们都是采用synchronized或者Lock方式解决多线程间的共享数据问题。这时多线程的运行都是在一个JVM之下，没有任何问题。
当时我们的应用是分布式集群工作的情况下，属于多JVM下的工作环境，跨JVM之间已经无法通过多线程的锁解决同步问题
这时需要一种更加高级的锁机制，来处理跨机器的进程之间的数据同步问题。
2、分布式锁原理
核心思想：当客户端获取锁，则创建节点，使用完锁，则删除节点
1）客户端获取锁时，在lock(随便哪个)节点下创建临时顺序节点
2）然后获取lock下的所有子节点，客户端获取到所有的子节点之后，如果发现自己创建的子节点序号最小，那么就认为该客户端获取到了锁，使用完锁后，该节点删除
3）如果发现自己创建的节点并非lock所有子节点中最小的，说明自己还没有获取到锁，此时客户端需要找到比自己小的那个节点，同时对其注册事件监听器，监听删除事件。
4）如果发现比自己小的那个节点被删除，则客户端的Watcher会收到相应的通知，此时再次判断自己创建的节点是否是lock子节点中序号最小的，重复3）步骤（不知道前面的顺序中还有比自己小的）如果是则获取到了锁.如果不是则重复以上的步骤继续获取比自己小的节点并注册监听.
3、Curator实现分布式锁
maven依赖：
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-framework</artifactId>
<version>2.13.0</version>
</dependency>
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-recipes</artifactId>
<version>2.13.0</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.21</version>
<scope>test</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/log4j/log4j -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>
代码：
public class TestLock {
public static void main(String[] args) {
Ticket12306 ticket = new Ticket12306();
new Thread(ticket,"携程").start();
new Thread(ticket,"飞猪").start();
}
}
import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.locks.InterProcessMutex;
import org.apache.curator.retry.ExponentialBackoffRetry;
import java.util.concurrent.TimeUnit;
public class Ticket12306 implements Runnable {
private Integer ticket = 10;
private InterProcessMutex lock;
public Ticket12306(){
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000,10);
CuratorFramework client = CuratorFrameworkFactory.newClient(
"192.168.42.134:2181",
60 * 1000,
15 * 1000,
retryPolicy
);
client.start();
lock = new InterProcessMutex(client,"/lock");
}
public void run() {
while(true){
try {
lock.acquire(3, TimeUnit.SECONDS);
if(ticket > 0){
System.out.println(Thread.currentThread().getName()+": "+ticket--);
}
Thread.sleep(500);
} catch (Exception e) {
e.printStackTrace();
}finally {
try {
lock.release();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
显示结果：
飞猪: 3
2021-12-18 16:50:22,788 13657 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x400000237160001, packet:: clientPath:null serverPath:null finished:false header:: 38,1 replyHeader:: 38,51539607621,0 request:: '/lock/_c_a4d5bb09-3655-40b3-8f3e-b8d4616c5c7c-lock-,#3139322e3136382e37332e31,v{s{31,s{'world,'anyone}}},3 response:: '/lock/_c_a4d5bb09-3655-40b3-8f3e-b8d4616c5c7c-lock-0000000031
2021-12-18 16:50:22,793 13662 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x400000237160001, packet:: clientPath:null serverPath:null finished:false header:: 39,12 replyHeader:: 39,51539607621,0 request:: '/lock,F response:: v{'_c_8231f736-89fb-4134-9d53-06bac741496d-lock-0000000030,'_c_a4d5bb09-3655-40b3-8f3e-b8d4616c5c7c-lock-0000000031},s{51539607558,51539607558,1639817196743,1639817196743,0,62,0,0,0,2,51539607621}
2021-12-18 16:50:22,797 13666 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x400000237160001, packet:: clientPath:null serverPath:null finished:false header:: 40,4 replyHeader:: 40,51539607621,0 request:: '/lock/_c_8231f736-89fb-4134-9d53-06bac741496d-lock-0000000030,T response:: #3139322e3136382e37332e31,s{51539607619,51539607619,1639817422951,1639817422951,0,0,0,288230385665835009,12,0,51539607619}
2021-12-18 16:50:23,290 14159 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Got notification sessionid:0x400000237160001
2021-12-18 16:50:23,290 14159 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Got WatchedEvent state:SyncConnected type:NodeDeleted path:/lock/_c_8231f736-89fb-4134-9d53-06bac741496d-lock-0000000030 for sessionid 0x400000237160001
2021-12-18 16:50:23,290 14159 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x400000237160001, packet:: clientPath:null serverPath:null finished:false header:: 41,2 replyHeader:: 41,51539607622,0 request:: '/lock/_c_8231f736-89fb-4134-9d53-06bac741496d-lock-0000000030,-1 response:: null
2021-12-18 16:50:23,292 14161 [68.42.134:2181)] DEBUG rg.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x400000237160001, packet:: clientPath:null serverPath:null finished:false header:: 42,12 replyHeader:: 42,51539607622,0 request:: '/lock,F response:: v{'_c_a4d5bb09-3655-40b3-8f3e-b8d4616c5c7c-lock-0000000031},s{51539607558,51539607558,1639817196743,1639817196743,0,63,0,0,0,1,51539607622}
携程: 2
....
在zookeeper的显示：
[_c_0d6114b0-f2e3-4dc6-a69c-29083d67cf04-lock-0000000082, _c_6fa35ef0-ecb6-4bcd-bbf2-0ea04994f6a0-lock-0000000081]
[zk: localhost:2181(CONNECTED) 9] ls /lock
[]
标签：12,lock,Zookeeper,curator,apache,null,节点,分布式 来源： https://blog.csdn.net/weixin_43725517/article/details/121917146