zookeeper（10）源碼分析-事件監聽Watcher（3）

今天繼續源碼分析，分析一下org.apache.zookeeper.server下的WatchManager類。

WatcherManager類用於管理watchers和相應的觸發器。

類的屬性

//watchTable表示從節點路徑到watcher集合的映射
    private final HashMap<String, HashSet<Watcher>> watchTable =
        new HashMap<String, HashSet<Watcher>>();
    //watch2Paths則表示從watcher到所有節點路徑集合的映射
    private final HashMap<Watcher, HashSet<String>> watch2Paths =
        new HashMap<Watcher, HashSet<String>>();

核心方法

1. size方法

size方法是同步的，因此在多線程環境下是安全的，其主要作用是獲取watchTable的大小，即遍歷watchTable的值集合，每個集合大小累加。

synchronized int size(){
        int result = 0;
        for(Set<Watcher> watches : watchTable.values()) {
            result += watches.size();
        }
        return result;
    }

2、addWatch方法

addWatch方法同樣是同步的，主要用來更新類裏面的上面提到的兩個集合屬性。

synchronized void addWatch(String path, Watcher watcher) {
        //通過傳入的path（節點路徑）從watchTable獲取相應的watcher集合
        HashSet<Watcher> list = watchTable.get(path);
        if (list == null) { //watcher是否爲空，若爲空
            // 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，並將路徑path和此集合添加至watchTable中
            list = new HashSet<Watcher>(4);
            watchTable.put(path, list);
        }
        //將傳入的watcher添加至watcher集合，即完成了path和watcher添加至watchTable的步驟
        list.add(watcher);
        //通過傳入的watcher從watch2Paths中獲取相應的path集合
        HashSet<String> paths = watch2Paths.get(watcher);
        if (paths == null) {// 判斷path集合是否爲空，若爲空
            // cnxns typically have many watches, so use default cap here
            //新生成path集合，並將watcher和paths添加至watch2Paths中
            paths = new HashSet<String>();
            watch2Paths.put(watcher, paths);
        }
        // 將傳入的path（節點路徑）添加至path集合，即完成了path和watcher添加至watch2Paths的步驟
        paths.add(path);
    }

3、removeWatcher

removeWatcher用作從watch2Paths和watchTable中中移除該watcher

synchronized void removeWatcher(Watcher watcher) {
        //從wach2Paths中移除watcher，並返回watcher對應的path集合
        HashSet<String> paths = watch2Paths.remove(watcher);
        if (paths == null) {
            return;
        }
        for (String p : paths) {
            //從watcherTable中根據路徑取出相應的watcher集合
            HashSet<Watcher> list = watchTable.get(p);
            if (list != null) {
                // 從list中移除該watcher
                list.remove(watcher);
                // 移除後list爲空，則從watchTable中移出path
                if (list.size() == 0) {
                    watchTable.remove(p);
                }
            }
        }
    }

4、triggerWatch

該方法主要用於觸發watch事件，並對事件進行處理。

Set<Watcher> triggerWatch(String path, EventType type) {
        return triggerWatch(path, type, null);
    }

    Set<Watcher> triggerWatch(String path, EventType type, Set<Watcher> supress) {
        // 根據事件類型、連接狀態、節點路徑創建WatchedEvent
        WatchedEvent e = new WatchedEvent(type,
                KeeperState.SyncConnected, path);
        HashSet<Watcher> watchers;
        synchronized (this) {
            // 從watcher表中移除path，並返回其對應的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;
            }
            // 遍歷watcher集合
            for (Watcher w : watchers) {
                // 根據watcher從watcher表中取出路徑集合
                HashSet<String> paths = watch2Paths.get(w);
                if (paths != null) {
                                // 如果paths不爲空，則移除傳入路徑path
                    paths.remove(path);
                }
            }
        }
        // 遍歷watcher集合
        for (Watcher w : watchers) {
            if (supress != null && supress.contains(w)) {
                continue;
            }
            // watcher進行處理
            w.process(e);
        }
        return watchers;
    }