zookeeper（9）源碼分析-事件監(jiān)聽(tīng)Watcher（2）

接著上一篇文章，繼續(xù)分析和Watcher相關(guān)的類(lèi)的源碼。

ClientWatchManager

public Set<Watcher> materialize(Watcher.Event.KeeperState state,
        Watcher.Event.EventType type, String path);

該接口，只有一個(gè)方法，需要實(shí)現(xiàn)。該方法表示事件發(fā)生時(shí)，返回需要被通知的Watcher集合，可能為空集合。

ZKWatchManager

1、ZKWatchManager是ZooKeeper的內(nèi)部類(lèi)，實(shí)現(xiàn)了ClientWatchManager。
2、ZKWatchManager定義了三個(gè)Map鍵值對(duì)，鍵為節(jié)點(diǎn)路徑，值為Watcher。分別對(duì)應(yīng)數(shù)據(jù)變化的Watcher、節(jié)點(diǎn)是否存在的Watcher、子節(jié)點(diǎn)變化的Watcher。

static class ZKWatchManager implements ClientWatchManager {
        //數(shù)據(jù)變化的watchers
        private final Map<String, Set<Watcher>> dataWatches =
            new HashMap<String, Set<Watcher>>();
        //節(jié)點(diǎn)存在與否的watchers
        private final Map<String, Set<Watcher>> existWatches =
            new HashMap<String, Set<Watcher>>();
        //子節(jié)點(diǎn)變化的watchers
        private final Map<String, Set<Watcher>> childWatches =
            new HashMap<String, Set<Watcher>>();

3、materialize方法

該方法在事件發(fā)生后，返回需要被通知的Watcher集合。在該方法中，首先會(huì)根據(jù)EventType類(lèi)型確定相應(yīng)的事件類(lèi)型，然后根據(jù)事件類(lèi)型的不同做出相應(yīng)的操作，如針對(duì)None類(lèi)型，即無(wú)任何事件，則首先會(huì)從三個(gè)鍵值對(duì)中刪除clientPath對(duì)應(yīng)的Watcher，然后將剩余的Watcher集合添加至結(jié)果集合；針對(duì)NodeDataChanged和NodeCreated事件而言，其會(huì)從dataWatches和existWatches中刪除clientPath對(duì)應(yīng)的Watcher，然后將剩余的Watcher集合添加至結(jié)果集合。

@Override
        public Set<Watcher> materialize(Watcher.Event.KeeperState state,
                                        Watcher.Event.EventType type,
                                        String clientPath)
        {
            //返回結(jié)果集合
            Set<Watcher> result = new HashSet<Watcher>();

            switch (type) {//事件類(lèi)型
            case None://無(wú)類(lèi)型
                //添加默認(rèn)watcher
                result.add(defaultWatcher);
                //根據(jù)disableAutoWatchReset和Zookeeper的狀態(tài)是否為同步連接判斷是否需要清空
                boolean clear = disableAutoWatchReset && state != Watcher.Event.KeeperState.SyncConnected;
                //針對(duì)3個(gè)不同的watcherMap進(jìn)行操作
                synchronized(dataWatches) {
                    for(Set<Watcher> ws: dataWatches.values()) {
                        // 添加至結(jié)果集合
                        result.addAll(ws);
                    }
                    if (clear) { // 是否需要清空
                        dataWatches.clear();
                    }
                }

                synchronized(existWatches) {
                    for(Set<Watcher> ws: existWatches.values()) {
                        result.addAll(ws);
                    }
                    if (clear) {
                        existWatches.clear();
                    }
                }

                synchronized(childWatches) {
                    for(Set<Watcher> ws: childWatches.values()) {
                        result.addAll(ws);
                    }
                    if (clear) {
                        childWatches.clear();
                    }
                }

                return result;
            case NodeDataChanged:// 節(jié)點(diǎn)數(shù)據(jù)變化
            case NodeCreated:// 創(chuàng)建節(jié)點(diǎn)
                synchronized (dataWatches) {
                    //移除clientPath對(duì)應(yīng)的Watcher后全部添加至結(jié)果集合
                    addTo(dataWatches.remove(clientPath), result);
                }
                synchronized (existWatches) {
                    //移除clientPath對(duì)應(yīng)的Watcher后全部添加至結(jié)果集合
                    addTo(existWatches.remove(clientPath), result);
                }
                break;
            case NodeChildrenChanged: // 節(jié)點(diǎn)子節(jié)點(diǎn)變化
                synchronized (childWatches) {
                    // 移除clientPath對(duì)應(yīng)的Watcher后全部添加至結(jié)果集合
                    addTo(childWatches.remove(clientPath), result);
                }
                break;
            case NodeDeleted:// 刪除節(jié)點(diǎn)
                synchronized (dataWatches) {
                    // 移除clientPath對(duì)應(yīng)的Watcher后全部添加至結(jié)果集合
                    addTo(dataWatches.remove(clientPath), result);
                }
                // XXX This shouldn't be needed, but just in case
                synchronized (existWatches) {
                    Set<Watcher> list = existWatches.remove(clientPath);
                    if (list != null) {
                        addTo(list, result);
                        LOG.warn("We are triggering an exists watch for delete! Shouldn't happen!");
                    }
                }
                synchronized (childWatches) {
                    //移除clientPath對(duì)應(yīng)的Watcher后全部添加至結(jié)果集合
                    addTo(childWatches.remove(clientPath), result);
                }
                break;
            default:
                String msg = "Unhandled watch event type " + type
                    + " with state " + state + " on path " + clientPath;
                LOG.error(msg);
                throw new RuntimeException(msg);
            }

            return result;
        }
    }