Distributed locking using Apache ZooKeeper and Apache Curator

• Distributed lock using Apache Curator client for Apache Zookeeper

  In this example we will see how to create distributed lock using Apache curator recipes.

  • We can setup development environment using in docker using this blog

Java Client Code that uses Apache Curator framework and recipe

 package com.artemis.demo;

import java.util.Date;

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.locks.InterProcessSemaphoreMutex;
import org.apache.curator.retry.RetryForever;
import org.apache.curator.retry.RetryNTimes;

public class DistributedLockWithCuratorRecipe {


     public static void main(String[] args) {

         RetryPolicy retryPolicy = new RetryNTimes(3, 100);
         CuratorFramework cf = CuratorFrameworkFactory.newClient("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183",
                  retryPolicy);
                  //alternate to retry
                  // new RetryForever(2000));
         cf.start();
         try {
            cf.blockUntilConnected();
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
         InterProcessSemaphoreMutex mutex = new InterProcessSemaphoreMutex(cf, "/curator/node");

         try {
           //we acquire lock first
            mutex.acquire(); // throws exception

            // Perform the business logic - mocking using Thread sleep
            System.err.print("D1 is acquired the lock");
            Date dt = new Date();
            System.out.println(dt.toString());

            Thread.sleep(30000);
            mutex.release();    
            System.err.print("D1 is released the lock");
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            cf.close();
        }
    }
}

Adding maven dependency

<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.8.0</version>
</dependency>

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-recipes</artifactId>
    <version>5.2.1</version>
</dependency>
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>5.2.1</version>
</dependency>

Execution

• If the above java class is executed as multiple process, we could see that when one process acquired the lock, the next process waits for lock to be released.
• This code is using the Curator InterProcessSemaphoreMutex shared lock, to make distributed process synchronized.