[Zookeeper学习笔记之六]Zookeeper源代码分析之Zookeeper.WatchRegistration
编程技术 / houtizong 发布于 3年前 57
Zookeeper类是Zookeeper提供给用户访问Zookeeper service的主要API，它包含了如下几个内部类
首先分析它的内部类，从WatchRegistration开始，为指定的znode path注册一个Watcher，
/** * Register a watcher for a particular path. */ abstract class WatchRegistration { //Watcher和clientPath组织在一起，一个Watcher对应一个具体的path，一个具体 //的path可以绑定多个Watcher？ private Watcher watcher; private String clientPath; public WatchRegistration(Watcher watcher, String clientPath) { this.watcher = watcher; this.clientPath = clientPath; } //获取Watcher集合，Map的key是clientPath //抽象类，需要实现类进行实现 abstract protected Map<String, Set<Watcher>> getWatches(int rc); /** * Register the watcher with the set of watches on path. * @param rc the result code of the operation that attempted to * add the watch on the path. */ public void register(int rc) { if (shouldAddWatch(rc)) { //抽象累默认rc为0，则添加，实现类可以改写 Map<String, Set<Watcher>> watches = getWatches(rc); synchronized(watches) {//实现类返回的watches必须为非null //获取clientPath对应的Watcher集合 Set<Watcher> watchers = watches.get(clientPath); if (watchers == null) {//Set唯恐，构造Set，并设置到Map中 watchers = new HashSet<Watcher>(); watches.put(clientPath, watchers); } //将watcher添加到Set中 watchers.add(watcher); } } } /** * Determine whether the watch should be added based on return code. * @param rc the result code of the operation that attempted to add the * watch on the node * @return true if the watch should be added, otw false */ protected boolean shouldAddWatch(int rc) { return rc == 0; } }
接下来简单下分析WatcherRegistration的实现类，
/** Handle the special case of exists watches - they add a watcher * even in the case where NONODE result code is returned. */ //一个zookeeper客户端调用Zookeeper.exists方法，即使znode不存在，也会添加监听这个znode的创建 //如果另外一个zookeeper客户端创建这个znode，上面的watcher也会收到这个事件 class ExistsWatchRegistration extends WatchRegistration { public ExistsWatchRegistration(Watcher watcher, String clientPath) { super(watcher, clientPath); } @Override protected Map<String, Set<Watcher>> getWatches(int rc) { //如果znode存在，那么返回Zookeeper的实例的watchManager实例的dataWatches,否则返回watchManager实例的existWatches //zookeeper的实例的watchManager实例的dataWatches和existWatches表示什么含义？？zookeeper应该把watcher进行了分类 //dataWatch表示数据变化类(NodeDataChangeEvent)的watch，existWatch表示存在类的watch return rc == 0 ? watchManager.dataWatches : watchManager.existWatches; } @Override protected boolean shouldAddWatch(int rc) { return rc == 0 || rc == KeeperException.Code.NONODE.intValue(); //znode不存在，调用zookeeper.exists也可以添加这个watcher， } }
DataWatchRegistration类
class DataWatchRegistration extends WatchRegistration { public DataWatchRegistration(Watcher watcher, String clientPath) { super(watcher, clientPath); } @Override protected Map<String, Set<Watcher>> getWatches(int rc) { //只返回Zookeeper对象的watchManager的dataWatches，dataWatches表示数据变化类(NodeDataChangeEvent)的watch return watchManager.dataWatches; } }
ChildWatchRegistration类
class ChildWatchRegistration extends WatchRegistration { public ChildWatchRegistration(Watcher watcher, String clientPath) { super(watcher, clientPath); } @Override protected Map<String, Set<Watcher>> getWatches(int rc) { //返回的是child变化事件，该Watcher设置在父节点上，子节点的添加和删除触发此事件 return watchManager.childWatches; } }
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