Javas使用Redlock实现分布式锁过程解析

一、redlock简介

在不同进程需要互斥地访问共享资源时，分布式锁是一种非常有用的技术手段。实现高效的分布式锁有三个属性需要考虑：

• 安全属性：互斥，不管什么时候，只有一个客户端持有锁
• 效率属性A:不会死锁
• 效率属性B：容错，只要大多数redis节点能够正常工作，客户端端都能获取和释放锁。

Redlock是redis官方提出的实现分布式锁管理器的算法。这个算法会比一般的普通方法更加安全可靠。关于这个算法的讨论可以看下官方文档。

二、怎么用java使用 redlock

在pom文件引入redis和redisson依赖：

<!-- redis-->
		<dependency>			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-redis</artifactId>
		</dependency>
		<!-- redisson-->
		<dependency>			<groupId>org.redisson</groupId>
			<artifactId>redisson</artifactId>
			<version>3.3.2</version>
		</dependency>

AquiredLockWorker接口类，，主要是用于获取锁后需要处理的逻辑：

/**
 * Created by fangzhipeng on 2017/4/5.
 * 获取锁后需要处理的逻辑
 */
public interface AquiredLockWorker<T> {
   T invokeAfterLockAquire() throws Exception;
}

DistributedLocker 获取锁管理类：

/**
 * Created by fangzhipeng on 2017/4/5.
 * 获取锁管理类
 */
public interface DistributedLocker {
   /**
   * 获取锁
   * @param resourceName 锁的名称
   * @param worker 获取锁后的处理类
   * @param <T>
   * @return 处理完具体的业务逻辑要返回的数据
   * @throws UnableToAquireLockException
   * @throws Exception
   */
   <T> T lock(String resourceName, AquiredLockWorker<T> worker) throws UnableToAquireLockException, Exception;

   <T> T lock(String resourceName, AquiredLockWorker<T> worker, int lockTime) throws UnableToAquireLockException, Exception;

}

UnableToAquireLockException ，不能获取锁的异常类：

/**
 * Created by fangzhipeng on 2017/4/5.
 * 异常类
 */
public class UnableToAquireLockException extends RuntimeException {

  public UnableToAquireLockException() {
  }

  public UnableToAquireLockException(String message) {
    super(message);
  }

  public UnableToAquireLockException(String message, Throwable cause) {
    super(message, cause);
  }
}

RedissonConnector 连接类：

/**
 * Created by fangzhipeng on 2017/4/5.
 * 获取RedissonClient连接类
 */
@Component
public class RedissonConnector {
  RedissonClient redisson;
  @PostConstruct
  public void init(){
    redisson = Redisson.create();
  }
  public RedissonClient getClient(){
    return redisson;
  }
}

RedisLocker 类，实现了DistributedLocker：

import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import java.util.concurrent.TimeUnit;

/**
 * Created by fangzhipeng on 2017/4/5.
 */
@Component
public class RedisLocker implements DistributedLocker{

  private final static String LOCKER_PREFIX = "lock:";

  @Autowired
  RedissonConnector redissonConnector;
  @Override
  public <T> T lock(String resourceName, AquiredLockWorker<T> worker) throws InterruptedException, UnableToAquireLockException, Exception {

    return lock(resourceName, worker, 100);
  }

  @Override
  public <T> T lock(String resourceName, AquiredLockWorker<T> worker, int lockTime) throws UnableToAquireLockException, Exception {
    RedissonClient redisson= redissonConnector.getClient();
    RLock lock = redisson.getLock(LOCKER_PREFIX + resourceName);
   // Wait for 100 seconds seconds and automatically unlock it after lockTime seconds
    boolean success = lock.tryLock(100, lockTime, TimeUnit.SECONDS);
    if (success) {
      try {
        return worker.invokeAfterLockAquire();
      } finally {
        lock.unlock();
      }
    }
    throw new UnableToAquireLockException();
  }
}

测试类：

 @Autowired
  RedisLocker distributedLocker;
  @RequestMapping(value = "/redlock")
  public String testRedlock() throws Exception{

    CountDownLatch startSignal = new CountDownLatch(1);
    CountDownLatch doneSignal = new CountDownLatch(5);
    for (int i = 0; i < 5; ++i) { // create and start threads
      new Thread(new Worker(startSignal, doneSignal)).start();
    }
    startSignal.countDown(); // let all threads proceed
    doneSignal.await();
    System.out.println("All processors done. Shutdown connection");
    return "redlock";
  }

   class Worker implements Runnable {
    private final CountDownLatch startSignal;
    private final CountDownLatch doneSignal;

    Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
      this.startSignal = startSignal;
      this.doneSignal = doneSignal;
    }

    public void run() {
      try {
        startSignal.await();
        distributedLocker.lock("test",new AquiredLockWorker<Object>() {

          @Override
          public Object invokeAfterLockAquire() {
            doTask();
            return null;
          }

        });
      }catch (Exception e){

      }
    }

    void doTask() {
      System.out.println(Thread.currentThread().getName() + " start");
      Random random = new Random();
      int _int = random.nextInt(200);
      System.out.println(Thread.currentThread().getName() + " sleep " + _int + "millis");
      try {
        Thread.sleep(_int);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println(Thread.currentThread().getName() + " end");
      doneSignal.countDown();
    }
  }

运行测试类：

Thread-48 start
Thread-48 sleep 99millis
Thread-48 end
Thread-49 start
Thread-49 sleep 118millis
Thread-49 end
Thread-52 start
Thread-52 sleep 141millis
Thread-52 end
Thread-50 start
Thread-50 sleep 28millis
Thread-50 end
Thread-51 start
Thread-51 sleep 145millis
Thread-51 end

从运行结果上看，在异步任务的情况下，确实是获取锁之后才能运行线程。不管怎么样，这是redis官方推荐的一种方案，可靠性比较高。有什么问题欢迎留言。

三、参考资料

https://github.com/redisson/redisson

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