edu.umass.cs.msocket.proxy.watchdog.WatchdogListScanner.java Source code

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/*******************************************************************************
 *
 * Mobility First - mSocket library
 * Copyright (C) 2013, 2014 - University of Massachusetts Amherst
 * Contact: arun@cs.umass.edu
 *
 * 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. 
 *
 * Initial developer(s): Arun Venkataramani, Aditya Yadav, Emmanuel Cecchet.
 * Contributor(s): ______________________.
 *
 *******************************************************************************/

package edu.umass.cs.msocket.proxy.watchdog;

import java.util.LinkedList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.json.JSONArray;

import edu.umass.cs.gns.client.GuidEntry;
import edu.umass.cs.gns.client.UniversalGnsClient;

/**
 * This class defines a WatchdogListScanner
 * 
 * @author <a href="mailto:cecchet@cs.umass.edu">Emmanuel Cecchet</a>
 * @version 1.0
 */
public class WatchdogListScanner extends Thread {
    private String listName;
    private List<String> guidList = new LinkedList<String>();
    private List<MembershipChangeCallback> callbacks = new LinkedList<MembershipChangeCallback>();
    private long refreshFrequencyInMs;
    private boolean isKilled = false;
    private UniversalGnsClient gnsClient;
    private GuidEntry watchdogGuid;
    private String targetGuid;
    private static final Logger logger = Logger.getLogger("Watchdog");

    /**
     * Creates a new <code>WatchdogListScanner</code> object
     * 
     * @param gnsClient GNS connection
     * @param watchdogGuid GUID entry for this watchdog service
     * @param targetGuid GUID of the listname we have to read
     * @param listName name of the field where the list is stored
     * @param refreshFrequencyInMs how often we should read the list
     */
    public WatchdogListScanner(UniversalGnsClient gnsClient, GuidEntry watchdogGuid, String targetGuid,
            String listName, long refreshFrequencyInMs) {
        this.gnsClient = gnsClient;
        this.watchdogGuid = watchdogGuid;
        this.targetGuid = targetGuid;
        this.listName = listName;
        this.refreshFrequencyInMs = refreshFrequencyInMs;
        logger.setLevel(Level.FINE);
    }

    /**
     * Register a callback to be notified of membership changes (additions or
     * deletions)
     * 
     * @param callback
     */
    public void registerMembershipChangeCallback(MembershipChangeCallback callback) {
        callbacks.add(callback);
    }

    /**
     * Unregister a previously registered callback
     * 
     * @param callback the callback to unregister
     * @return true if the callback was removed, false if it has not been found
     */
    public boolean unregisterMembershipChangeCallback(MembershipChangeCallback callback) {
        return callbacks.remove(callback);
    }

    /**
     * Call this method to terminate the thread
     */
    public void killIt() {
        isKilled = true;
    }

    /**
     * @see java.lang.Thread#run()
     */
    @Override
    public void run() {
        long last = System.currentTimeMillis();
        while (!isKilled) {
            long sleepFor = last + refreshFrequencyInMs - System.currentTimeMillis();
            if (sleepFor > 0)
                try {
                    Thread.sleep(sleepFor);
                } catch (InterruptedException ignore) {
                }

            last = System.currentTimeMillis();
            try {
                logger.fine("Fetching " + listName);
                JSONArray guids = gnsClient.fieldRead(targetGuid, listName, watchdogGuid);
                // Duplicate the list in a friendly format
                List<String> newList = new LinkedList<String>();
                for (int i = 0; i < guids.length(); i++) {
                    String guid = guids.getString(i);
                    newList.add(guid);
                }

                // Look for additions
                for (String guid : newList) {
                    if (!guidList.contains(guid)) {
                        logger.fine("Found new guid " + guid + " in list " + listName);
                        guidList.add(guid);
                        // Notify callbacks
                        for (MembershipChangeCallback callback : callbacks) {
                            callback.memberAddedCallback(guid, listName);
                        }
                    }
                }
                // Look for removal
                for (String guid : guidList) {
                    if (!newList.contains(guid)) {
                        logger.fine(guid + " is no more in list " + listName);
                        // Notify callbacks
                        for (MembershipChangeCallback callback : callbacks) {
                            callback.memberRemovedCallback(guid, listName);
                        }
                    }
                }

                // Switch to the new list
                guidList = newList;
            } catch (Exception e) {
                logger.log(Level.WARNING, "Failed to read list " + listName + " in GUID " + targetGuid, e);
            }
        }
    }

    /**
     * Returns the listName value.
     * 
     * @return Returns the listName.
     */
    public String getListName() {
        return listName;
    }

    /**
     * Returns the guidList value.
     * 
     * @return Returns the guidList.
     */
    public List<String> getGuidList() {
        return guidList;
    }

    /**
     * Returns the refreshFrequencyInMs value.
     * 
     * @return Returns the refreshFrequencyInMs.
     */
    public long getRefreshFrequencyInMs() {
        return refreshFrequencyInMs;
    }

}