zookeeper（10）源码分析-事件监听Watcher（3）-创新互联
今天继续源码分析，分析一下org.apache.zookeeper.server下的WatchManager类。
WatcherManager类用于管理watchers和相应的触发器。
类的属性
//watchTable表示从节点路径到watcher集合的映射
private final HashMap> watchTable =
new HashMap>();
//watch3Paths则表示从watcher到所有节点路径集合的映射
private final HashMap> watch3Paths =
new HashMap>(); 核心方法
1. size方法
size方法是同步的，因此在多线程环境下是安全的，其主要作用是获取watchTable的大小，即遍历watchTable的值集合，每个集合大小累加。
synchronized int size(){
int result = 0;
for(Set watches : watchTable.values()) {
result += watches.size();
}
return result;
} 2、addWatch方法
addWatch方法同样是同步的，主要用来更新类里面的上面提到的两个集合属性。
synchronized void addWatch(String path, Watcher watcher) {
//通过传入的path（节点路径）从watchTable获取相应的watcher集合
HashSet list = watchTable.get(path);
if (list == null) { //watcher是否为空，若为空
// don't waste memory if there are few watches on a node
// rehash when the 4th entry is added, doubling size thereafter
// seems like a good compromise
//新生成watcher集合，并将路径path和此集合添加至watchTable中
list = new HashSet(4);
watchTable.put(path, list);
}
//将传入的watcher添加至watcher集合，即完成了path和watcher添加至watchTable的步骤
list.add(watcher);
//通过传入的watcher从watch3Paths中获取相应的path集合
HashSet paths = watch3Paths.get(watcher);
if (paths == null) {// 判断path集合是否为空，若为空
// cnxns typically have many watches, so use default cap here
//新生成path集合，并将watcher和paths添加至watch3Paths中
paths = new HashSet();
watch3Paths.put(watcher, paths);
}
// 将传入的path（节点路径）添加至path集合，即完成了path和watcher添加至watch3Paths的步骤
paths.add(path);
} 3、removeWatcher
removeWatcher用作从watch3Paths和watchTable中中移除该watcher
synchronized void removeWatcher(Watcher watcher) {
//从wach3Paths中移除watcher，并返回watcher对应的path集合
HashSet paths = watch3Paths.remove(watcher);
if (paths == null) {
return;
}
for (String p : paths) {
//从watcherTable中根据路径取出相应的watcher集合
HashSet list = watchTable.get(p);
if (list != null) {
// 从list中移除该watcher
list.remove(watcher);
// 移除后list为空，则从watchTable中移出path
if (list.size() == 0) {
watchTable.remove(p);
}
}
}
} 4、triggerWatch
该方法主要用于触发watch事件，并对事件进行处理。
Set triggerWatch(String path, EventType type) {
return triggerWatch(path, type, null);
}
Set triggerWatch(String path, EventType type, Set supress) {
// 根据事件类型、连接状态、节点路径创建WatchedEvent
WatchedEvent e = new WatchedEvent(type,
KeeperState.SyncConnected, path);
HashSet watchers;
synchronized (this) {
// 从watcher表中移除path，并返回其对应的watcher集合
watchers = watchTable.remove(path);
if (watchers == null || watchers.isEmpty()) {
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG,
ZooTrace.EVENT_DELIVERY_TRACE_MASK,
"No watchers for " + path);
}
return null;
}
// 遍历watcher集合
for (Watcher w : watchers) {
// 根据watcher从watcher表中取出路径集合
HashSet paths = watch3Paths.get(w);
if (paths != null) {
// 如果paths不为空，则移除传入路径path
paths.remove(path);
}
}
}
// 遍历watcher集合
for (Watcher w : watchers) {
if (supress != null && supress.contains(w)) {
continue;
}
// watcher进行处理
w.process(e);
}
return watchers;
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