ZooKeeper ： Curator框架之分布式锁InterProcessMutex

Posted 2022-02-07 ITKaven

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InterProcessMutex

InterProcessMutex类的源码注释：

A re-entrant mutex that works across JVMs. Uses Zookeeper to hold the lock. All processes in all JVMs that use the same lock path will achieve an inter-process critical section. Further, this mutex is “fair” - each user will get the mutex in the order requested (from ZK’s point of view).

跨JVM工作的可重入互斥锁。使用Zookeeper来持有锁。所有JVM中使用相同锁路径的所有进程都将实现进程间临界区。此外，这个互斥锁是“公平的”—每个用户都将按照请求的顺序获得互斥锁（从ZK的角度来看）。

测试

pom.xml：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.kaven</groupId>
    <artifactId>zookeeper</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>5.2.0</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.22</version>
        </dependency>
    </dependencies>
</project>

CuratorFrameworkProperties类（提供CuratorFramework需要的一些配置信息）：

package com.kaven.zookeeper;

import org.apache.curator.RetryPolicy;
import org.apache.curator.retry.ExponentialBackoffRetry;

public class CuratorFrameworkProperties 
    // 连接地址
    public static final String CONNECT_ADDRESS = "192.168.1.3:9000";
    // 连接超时时间
    public static final int CONNECTION_TIMEOUT_MS = 40000;
    // Session超时时间
    public static final int SESSION_TIMEOUT_MS = 10000;
    // 命名空间
    public static final String NAMESPACE = "MyNamespace";
    // 重试策略
    public static final RetryPolicy RETRY_POLICY = new ExponentialBackoffRetry(1000, 3);

InterProcessMutexRunnable类（实现了Runnable接口，模拟分布式节点获取分布式锁）：

package com.kaven.zookeeper;

import lombok.SneakyThrows;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.imps.CuratorFrameworkState;
import org.apache.curator.framework.recipes.locks.InterProcessMutex;
import java.util.Random;

public class InterProcessMutexRunnable implements Runnable
    @SneakyThrows
    @Override
    public void run() 
        // 使用不同的CuratorFramework实例，表示不同的分布式节点
        CuratorFramework curator = getCuratorFramework();
        curator.start();
        assert curator.getState().equals(CuratorFrameworkState.STARTED);

        // 模拟随机加入的分布式节点
        int randomSleep = new Random().nextInt(1000);
        Thread.sleep(randomSleep);

        // 分布式锁的锁路径
        String path = "/kaven";

        // 创建InterProcessMutex实例，用于获取分布式锁
        InterProcessMutex mutex = new InterProcessMutex(curator, path);
        // 阻塞，直到获取分布式锁
        mutex.acquire();
        if(mutex.isOwnedByCurrentThread()) 
            System.out.println(Thread.currentThread().getName() + " 持有分布式锁");
            mutex.getParticipantNodes().forEach(System.out::println);
            // 处理业务
            Thread.sleep(5000);
            // 业务处理完成
            System.out.println(Thread.currentThread().getName() + " 业务处理完成");
            // 释放分布式锁
            mutex.release();
        
        else 
            throw new RuntimeException("获取分布式锁时被中断");
        
    

    private CuratorFramework getCuratorFramework() 

        // 创建CuratorFramework实例
        return CuratorFrameworkFactory.builder()
                .connectString(CuratorFrameworkProperties.CONNECT_ADDRESS)
                .retryPolicy(CuratorFrameworkProperties.RETRY_POLICY)
                .connectionTimeoutMs(CuratorFrameworkProperties.CONNECTION_TIMEOUT_MS)
                .sessionTimeoutMs(CuratorFrameworkProperties.SESSION_TIMEOUT_MS)
                .namespace(CuratorFrameworkProperties.NAMESPACE)
                .build();

启动类：

package com.kaven.zookeeper;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Application 
    private static final ExecutorService EXECUTOR_SERVICE = Executors.newCachedThreadPool();

    public static void main(String[] args) throws Exception 
        for (int i = 0; i < 5; i++) 
            EXECUTOR_SERVICE.execute(new InterProcessMutexRunnable());
        
        Thread.sleep(10000000);

模拟5个分布式节点获取分布式锁，输出如下所示：

pool-1-thread-4 持有分布式锁
/kaven/_c_e1940de6-9e12-4c94-8c1e-98d22178a94e-lock-0000000000
/kaven/_c_b53a7f04-2e85-4675-839a-c26d24585f2c-lock-0000000001
/kaven/_c_ad36f188-8d5b-4c8f-878b-2675dfb2e3ee-lock-0000000002
/kaven/_c_e843c51c-acf6-431f-b02a-479f7423c4d3-lock-0000000003
/kaven/_c_f594e331-b10d-4447-a475-6fd809d1b8c6-lock-0000000004
pool-1-thread-4 业务处理完成
pool-1-thread-5 持有分布式锁
/kaven/_c_b53a7f04-2e85-4675-839a-c26d24585f2c-lock-0000000001
/kaven/_c_ad36f188-8d5b-4c8f-878b-2675dfb2e3ee-lock-0000000002
/kaven/_c_e843c51c-acf6-431f-b02a-479f7423c4d3-lock-0000000003
/kaven/_c_f594e331-b10d-4447-a475-6fd809d1b8c6-lock-0000000004
pool-1-thread-5 业务处理完成
pool-1-thread-2 持有分布式锁
/kaven/_c_ad36f188-8d5b-4c8f-878b-2675dfb2e3ee-lock-0000000002
/kaven/_c_e843c51c-acf6-431f-b02a-479f7423c4d3-lock-0000000003
/kaven/_c_f594e331-b10d-4447-a475-6fd809d1b8c6-lock-0000000004
pool-1-thread-2 业务处理完成
pool-1-thread-1 持有分布式锁
/kaven/_c_e843c51c-acf6-431f-b02a-479f7423c4d3-lock-0000000003
/kaven/_c_f594e331-b10d-4447-a475-6fd809d1b8c6-lock-0000000004
pool-1-thread-1 业务处理完成
pool-1-thread-3 持有分布式锁
/kaven/_c_f594e331-b10d-4447-a475-6fd809d1b8c6-lock-0000000004
pool-1-thread-3 业务处理完成

InterProcessMutex类提供了两种方法来获取分布式锁：

    /**
     * 阻塞，直到获取分布式锁
     * 同一个线程可以重复获取该锁，即可重入锁
     * 每次获取锁都必须通过调用release()方法来释放锁
     */
    @Override
    public void acquire() throws Exception
    
        if ( !internalLock(-1, null) )
        
            throw new IOException("Lost connection while trying to acquire lock: " + basePath);
        
    

    /**
     * 阻塞，直到获取分布式锁或给定时间已到
     * 同一个线程可以重复获取该锁，即可重入锁
     * 每次获取锁都必须通过调用release()方法来释放锁
     */
    @Override
    public boolean acquire(long time, TimeUnit unit) throws Exception
    
        return internalLock(time, unit);

acquire(long time, TimeUnit unit)方法后面会演示。

可重入锁

    @SneakyThrows
    @Override
    public void run() 
    
        ...
        
        // 阻塞，直到获取分布式锁
        mutex.acquire();
        if(mutex.isOwnedByCurrentThread()) 
            System.out.println(Thread.currentThread().getName() + " 持有分布式锁");
            mutex.getParticipantNodes().forEach(System.out::println);
            // 处理业务
            reentry(5, mutex);
            // 业务处理完成
            System.out.println(Thread.currentThread().getName() + " 业务处理完成");
            // 释放分布式锁
            mutex.release();
        
        else 
            throw new RuntimeException("获取分布式锁时被中断");
        
    

    private void reentry(int nums, InterProcessMutex mutex) throws Exception 
        if(nums == 0) return;
        // 重复获取锁
        mutex.acquire();
        Thread.sleep(1000);
        reentry(nums - 1, mutex);
        // 每获取一次锁，都需要释放
        mutex.release();

通过递归调用来模拟锁重入，输出如下所示：

pool-1-thread-4 持有分布式锁
/kaven/_c_90f9c755-249e-4d80-a101-98d7c894b5bc-lock-0000000000
/kaven/_c_a86b8fc8-e5e0-40fa-9cb0-d25a82e55926-lock-0000000001
/kaven/_c_e2a8e273-e728-4e43-9261-3bd5933d73c8-lock-0000000002
/kaven/_c_9e08256f-cef1-40c4-9d76-9675d92a84e3-lock-0000000003
/kaven/_c_3704bb49-1470-4c4e-a03d-66737967cbff-lock-0000000004
pool-1-thread-4 业务处理完成
pool-1-thread-2 持有分布式锁
/kaven/_c_a86b8fc8-e5e0-40fa-9cb0-d25a82e55926-lock-0000000001
/kaven/_c_e2a8e273-e728-4e43-9261-3bd5933d73c8-lock-0000000002
/kaven/_c_9e08256f-cef1-40c4-9d76-9675d92a84e3-lock-0000000003
/kaven/_c_3704bb49-1470-4c4e-a03d-66737967cbff-lock-0000000004
pool-1-thread-2 业务处理完成
pool-1-thread-3 持有分布式锁
/kaven/_c_e2a8e273-e728-4e43-9261-3bd5933d73c8-lock-0000000002
/kaven/_c_9e08256f-cef1-40c4-9d76-9675d92a84e3-lock-0000000003
/kaven/_c_3704bb49-1470-4c4e-a03d-66737967cbff-lock-0000000004
pool-1-thread-3 业务处理完成
pool-1-thread-5 持有分布式锁
/kaven/_c_9e08256f-cef1-40c4-9d76-9675d92a84e3-lock-0000000003
/kaven/_c_3704bb49-1470-4c4e-a03d-66737967cbff-lock-0000000004
pool-1-thread-5 业务处理完成
pool-1-thread-1 持有分布式锁
/kaven/_c_3704bb49-1470-4c4e-a03d-66737967cbff-lock-0000000004
pool-1-thread-1 业务处理完成

可撤销锁

InterProcessMutex类实现了Revocable接口，使得锁可撤销，其实就是想要获取锁的用户给持有锁的用户发送一个请求（通过Curator的CuratorWatcher），持有锁的用户接收到这个请求后就可以进行处理，比如直接释放锁、平滑释放锁（处理完当前业务后再释放锁）甚至可以不理会该请求，因此这种撤销操作是合作完成的。


/**
 * 指定可以撤销的锁
 */
public interface Revocable<T>

    /**
     * 使锁可撤销
     * 当另一个进程/线程希望持有锁的用户释放锁时，该用户的监听器将被调用
     */
    public void     makeRevocable(RevocationListener<T> listener);
    public void     makeRevocable(RevocationListener<T> listener, Executor executor);

博主感觉这个功能不是很方便，撤销锁时需要知道持有锁的路径，而InterProcessMutex类并没有提供该路径的直接获取方法，博主只能通过获取参与竞争分布式锁的节点列表来完成该操作（获取该列表的第一个值，就是持有锁的路径），但这样做不是很方便，并且性能不太好。

    @SneakyThrows
    @Override
    public void run() 
    
        ...

        // 创建InterProcessMutex实例，用于获取分布式锁
        InterProcessMutex mutex = new InterProcessMutex(curator, path);
        // 本线程是否持有锁
        AtomicBoolean locked = new AtomicBoolean(false);
        mutex.makeRevocable((mtx) -> 
            // 接收到撤销锁的请求
            try 
                System.out.println(Thread.currentThread().getName() + " 接收到撤销锁的请求");
                if(locked.get()) 
                    // 直接释放锁
                    locked.set(false);
                    System.out.println(Thread.currentThread().getName() + " 直接释放分布式锁");
                
             catch (Exception e) 
                e.printStackTrace();
            
        );
        // 阻塞，直到获取分布式锁或给定时间已到
        mutex.acquire(8, TimeUnit.SECONDS);
        if(mutex.isOwnedByCurrentThread()) 
            locked.set(true);
            System.out.println(Thread.currentThread()Curator实现zookeeper分布式锁的基本原理
 第三章 zookeeper客户端-curator详解
 ZooKeeper ： Curator框架之共享计数器DistributedAtomicLong
 分布式锁-curator实现
 curator
 Curator的使用