net.spy.memcached.CacheMonitor.java Source code

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Here is the source code for net.spy.memcached.CacheMonitor.java

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/*
 * arcus-java-client : Arcus Java client
 * Copyright 2010-2014 NAVER Corp.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.spy.memcached;

import java.util.List;

import net.spy.memcached.compat.SpyObject;

import org.apache.zookeeper.AsyncCallback.ChildrenCallback;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

/**
 * CacheMonitor monitors the changes of the cache server list
 * in the ZooKeeper node(/arcus/cache_list/<service_code>).
 */
public class CacheMonitor extends SpyObject implements Watcher, ChildrenCallback {

    ZooKeeper zk;

    String cacheListZPath;

    String serviceCode;

    volatile boolean dead;

    CacheMonitorListener listener;

    /**
     * Constructor
     * 
     * @param zk
     *            ZooKeeper connection
     * @param serviceCode
     *            service code (or cloud name) to identify each cloud
     * @param listener
     *            Callback listener
     */
    public CacheMonitor(ZooKeeper zk, String cacheListZPath, String serviceCode, CacheMonitorListener listener) {
        this.zk = zk;
        this.cacheListZPath = cacheListZPath;
        this.serviceCode = serviceCode;
        this.listener = listener;

        getLogger().info("Initializing the CacheMonitor.");

        // Get the cache list from the Arcus admin asynchronously.
        // Returning list would be processed in processResult().
        asyncGetCacheList();
    }

    /**
     * Other classes use the CacheMonitor by implementing this method
     */
    public interface CacheMonitorListener {
        /**
         * The existing children of the node has changed.
         */
        void commandNodeChange(List<String> children);

        List<String> getPrevChildren();

        /**
         * The ZooKeeper session is no longer valid.
         */
        void closing();
    }

    /**
     * Processes every events from the ZooKeeper.
     */
    public void process(WatchedEvent event) {
        if (event.getType() == Event.EventType.None) {
            // Processes session events
            switch (event.getState()) {
            case SyncConnected:
                getLogger().warn("Reconnected to the Arcus admin. " + getInfo());
                return;
            case Disconnected:
                getLogger().warn("Disconnected from the Arcus admin. Trying to reconnect. " + getInfo());
                return;
            case Expired:
                // If the session was expired, just shutdown this client to be re-initiated.
                getLogger().warn("Session expired. Trying to reconnect to the Arcus admin." + getInfo());
                shutdown();
                return;
            }
        } else {
            // Set a new watch on the znode when there are any changes in it.
            if (event.getType() == Event.EventType.NodeChildrenChanged) {
                asyncGetCacheList();
            }
        }
    }

    /**
     * A callback function to process the result of getChildren(watch=true).
     */
    public void processResult(int rc, String path, Object ctx, List<String> children) {
        switch (Code.get(rc)) {
        case OK:
            listener.commandNodeChange(children);
            return;
        case NONODE:
            getLogger().fatal("Cannot find your service code. Please contact Arcus support to solve this problem. "
                    + getInfo());
            return;
        case SESSIONEXPIRED:
            getLogger().warn("Session expired. Trying to reconnect to the Arcus admin. " + getInfo());
            shutdown();
            return;
        case NOAUTH:
            getLogger().fatal("Authorization failed " + getInfo());
            shutdown();
            return;
        case CONNECTIONLOSS:
            getLogger().warn("Connection lost. Trying to reconnect to the Arcus admin." + getInfo());
            asyncGetCacheList();
            return;
        default:
            getLogger().warn(
                    "Ignoring an unexpected event from the Arcus admin. code=" + Code.get(rc) + ", " + getInfo());
            asyncGetCacheList();
            return;
        }
    }

    /**
     * Get the cache list asynchronously from the Arcus admin.
     */
    void asyncGetCacheList() {
        if (getLogger().isDebugEnabled()) {
            getLogger().debug("Set a new watch on " + (cacheListZPath + serviceCode));
        }

        zk.getChildren(cacheListZPath + serviceCode, true, this, null);
    }

    /**
     * Shutdown the CacheMonitor.
     */
    public void shutdown() {
        getLogger().info("Shutting down the CacheMonitor. " + getInfo());
        dead = true;
        listener.closing();
    }

    private String getInfo() {
        String zkSessionId = null;
        if (zk != null) {
            zkSessionId = "0x" + Long.toHexString(zk.getSessionId());
        }
        return "[serviceCode=" + serviceCode + ", adminSessionId=" + zkSessionId + "]";
    }
}