curator简介
Netflix curator 是Netflix公司开源的一个Zookeeper client library，用于简化zookeeper客户端编程，包含一下几个模块：
- curator-client - zookeeper client封装，用于取代原生的zookeeper客户端，提供一些非常有用的客户端特性
- curator-framework - zookeeper api的高层封装，大大简化zookeeper客户端编程，添加了例如zookeeper连接管理、重试机制等
- curator-recipes - zookeeper recipes 基于curator-framework的实现（除2PC以外）
maven dependency:
- <dependency>
- <groupId>com.netflix.curator</groupId>
- <artifactId>curator-recipes</artifactId>
- <version>0.6.4</version>
- </dependency>
注意：在www.mvnrepository.com中认为0.32为最新版本，其实迄今为止最新版本为0.64，github trunk中的版本现在是0.65-SNAPSHOT
curator framework 使用
示例代码：
- String path = "/test_path";
- CuratorFramework client = CuratorFrameworkFactory.builder()
- .connectString("test:2181").namespace("/test1")
- .retryPolicy(new RetryNTimes(Integer.MAX_VALUE, 1000))
- .connectionTimeoutMs(5000).build();
- //create a node
- client.create().forPath("/head", new byte[0]);
- //delete a node in background
- client.delete().inBackground().forPath("/head");
- // create a EPHEMERAL_SEQUENTIAL
- client.create().withMode(CreateMode.EPHEMERAL_SEQUENTIAL).forPath("/head/child", new byte[0]);
- // get the data
- client.getData().watched().inBackground().forPath("/test");
- // check the path exits
- client.checkExists().forPath(path);
curator framework使用builder模式和类似nio的chain api，代码非常简洁
curator recipes 使用
InterProcessMutex
用途：进程间互斥锁
示例代码：
- String lockName = "/lock1";
- InterProcessLock lock1 = new InterProcessMutex(this.curator, lockName);
- InterProcessLock lock2 = new InterProcessMutex(this.curator, lockName);
- lock1.acquire();
- boolean result = lock2.acquire(1, TimeUnit.SECONDS);
- assertFalse(result);
- lock1.release();
- result = lock2.acquire(1, TimeUnit.SECONDS);
- assertTrue(result);
原理：每次调用acquire在/lock1节点节点下使用CreateMode.EPHEMERAL_SEQUENTIAL 创建新的ephemeral节点，然后getChildren获取所有的children，判断刚刚创建的临时节点是否为第一个，如果是，则获取锁成功；如果不是，则删除刚刚创建的临时节点。
注意： 每次accquire操作，成功，则请求zk server 2次（一次写，一次getChildren）；如果失败，则请求zk server 3次（一次写，一次getChildren，一次delete）
InterProcessReadWriteLock
示例代码：
- @Test
- public void testReadWriteLock() throws Exception{
- String readWriteLockPath = "/RWLock";
- InterProcessReadWriteLock readWriteLock1 = new InterProcessReadWriteLock(this.curator, readWriteLockPath);
- InterProcessMutex writeLock1 = readWriteLock1.writeLock();
- InterProcessMutex readLock1 = readWriteLock1.readLock();
- InterProcessReadWriteLock readWriteLock2 = new InterProcessReadWriteLock(this.curator, readWriteLockPath);
- InterProcessMutex writeLock2 = readWriteLock2.writeLock();
- InterProcessMutex readLock2 = readWriteLock2.readLock();
- writeLock1.acquire();
- // same with WriteLock, can read
- assertTrue(readLock1.acquire(1, TimeUnit.SECONDS));
- // different lock, can't read while writting
- assertFalse(readLock2.acquire(1, TimeUnit.SECONDS));
- // different write lock, can't write
- assertFalse(writeLock2.acquire(1, TimeUnit.SECONDS));
- // release the write lock
- writeLock1.release();
- //both read lock can read
- assertTrue(readLock1.acquire(1, TimeUnit.SECONDS));
- assertTrue(readLock2.acquire(1, TimeUnit.SECONDS));
- }
原理： 同InterProcessMutext，在ephemeral node的排序算法上做trick，write lock的排序在前。
注意： 同一个InterProcessReadWriteLock如果已经获取了write lock，则获取read lock也会成功
LeaderSelector
示例代码：
- @Test
- public void testLeader() throws Exception{
- LeaderSelectorListener listener = new LeaderSelectorListener(){
- @Override
- public void takeLeadership(CuratorFramework client)
- throws Exception {
- System.out.println("i'm leader");
- }
- @Override
- public void handleException(CuratorFramework client,
- Exception exception) {
- }
- @Override
- public void notifyClientClosing(CuratorFramework client) {
- }};
- String leaderPath = "/leader";
- LeaderSelector selector1 = new LeaderSelector(this.curator, leaderPath, listener);
- selector1.start();
- LeaderSelector selector2 = new LeaderSelector(this.curator, leaderPath, listener);
- selector2.start();
- assertFalse(selector2.hasLeadership());
- }
原理：内部基于InterProcessMutex实现，具体细节参见shared lock一节
总结
curator还提供了很多其他的实现，具体参见https://github.com/Netflix/curator/wiki/Recipes