/*
* Funambol is a mobile platform developed by Funambol, Inc.
* Copyright (C) 2011 Funambol, Inc.
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU Affero General Public License version 3 as published by
* the Free Software Foundation with the addition of the following permission
* added to Section 15 as permitted in Section 7(a): FOR ANY PART OF THE COVERED
* WORK IN WHICH THE COPYRIGHT IS OWNED BY FUNAMBOL, FUNAMBOL DISCLAIMS THE
* WARRANTY OF NON INFRINGEMENT OF THIRD PARTY RIGHTS.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program; if not, see http://www.gnu.org/licenses or write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02110-1301 USA.
*
* You can contact Funambol, Inc. headquarters at 643 Bair Island Road, Suite
* 305, Redwood City, CA 94063, USA, or at email address info@funambol.com.
*
* The interactive user interfaces in modified source and object code versions
* of this program must display Appropriate Legal Notices, as required under
* Section 5 of the GNU Affero General Public License version 3.
*
* In accordance with Section 7(b) of the GNU Affero General Public License
* version 3, these Appropriate Legal Notices must retain the display of the
* "Powered by Funambol" logo. If the display of the logo is not reasonably
* feasible for technical reasons, the Appropriate Legal Notices must display
* the words "Powered by Funambol".
*/
package com.funambol.util.bus;
import com.funambol.util.Log;
import java.lang.ref.WeakReference;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;
/**
* Represents a simple bus communication framework which allows handlers to
* register for incoming messages of a specific type.
*
* Handlers can be registered using a Class type.
* If you register a handler for the type BusMessage it will be notified of all
* the incoming messages.
* If you register a handler for the type TypifiedBusMessage which is a subclass
* of BusMessage, it will be notified of the incoming messages of type
* BusMessage or TypifiedBusMessage, not any other message types.
*
* This class implementation is thread safe.
*/
public class Bus {
private static Bus instance = null;
private static final String TAG_LOG = "Bus";
private Hashtable handlers = new Hashtable();
private MessageQueue messageQueue = new MessageQueue();
private final Object handlersLock = new Object();
private final Object messageQueueLock = new Object();
private Bus() {
// Init/start the message queue runner
Thread messageQueueThread = new Thread(new MessageQueueRunner());
messageQueueThread.setDaemon(true);
messageQueueThread.start();
// Allow the daemon to start. This is especially important for unit test
// and has no real impact on client's implementations
do {
try {
Thread.yield();
Thread.sleep(100);
} catch (Exception e) {
}
} while(!messageQueueThread.isAlive());
}
/**
* @return the current bus instance
*/
public static synchronized Bus getInstance() {
if(instance == null) {
instance = new Bus();
}
return instance;
}
/**
* Register a new BusMessageHandler object for the given message type.
* Handler objects are stored using weak references to avoid memory leaks.
*
* @param type The message type
* @param handler The new BusMessageHandler object to register
* @return true if the handler has been registered
*/
public boolean registerMessageHandler(Class type, BusMessageHandler handler) {
if (Log.isLoggable(Log.TRACE)) {
Log.trace(TAG_LOG, "register message handler for type " + type);
}
synchronized(handlersLock) {
Vector typeHandlers = (Vector)handlers.get(type);
if(typeHandlers == null) {
typeHandlers = new Vector();
}
if(findMessageHandler(type, handler) != null) {
// Already registered
return false;
}
WeakReference wrHandler = new WeakReference(handler);
typeHandlers.addElement(wrHandler);
handlers.put(type, typeHandlers);
return true;
}
}
/**
* Unregister an existing BusMessageHandler object for the given message type.
*
* @param type The message type
* @param handler The BusMessageHandler object to unregister
* @return true if the handler has been unregistered
*/
public boolean unregisterMessageHandler(Class type, BusMessageHandler handler) {
if (Log.isLoggable(Log.TRACE)) {
Log.trace(TAG_LOG, "unregister message handler for type " + type);
}
synchronized(handlersLock) {
Vector typeHandlers = (Vector)handlers.get(type);
if(typeHandlers != null) {
WeakReference wrHandler = findWRMessageHandler(type, handler);
if(wrHandler != null) {
typeHandlers.removeElement(wrHandler);
handlers.put(type, typeHandlers);
return true;
}
}
return false;
}
}
public static void dispose() {
instance = null;
}
/**
* Send the given message to the registered handlers. A call to this method
* is asynchronous and will return immediately.
*
* @param message The message to send
*/
public void sendMessage(BusMessage message) {
if (Log.isLoggable(Log.TRACE)) {
Log.trace(TAG_LOG, "sending message " + message);
}
synchronized(messageQueueLock) {
messageQueue.add(message);
messageQueueLock.notifyAll();
}
}
// Send the given message to all the related handlers
private void dispatchMessage(BusMessage message) {
synchronized(handlersLock) {
Enumeration types = handlers.keys();
while(types.hasMoreElements()) {
Class type = (Class)types.nextElement();
if(type.isInstance(message)) {
Vector typeHandlers = (Vector)handlers.get(type);
dispatchMessageToHandlers(message, typeHandlers);
}
}
}
}
private void dispatchMessageToHandlers(BusMessage message, Vector handlers) {
Enumeration elements = handlers.elements();
while(elements.hasMoreElements()) {
WeakReference wrHandler = (WeakReference)elements.nextElement();
BusMessageHandler handler = (BusMessageHandler)wrHandler.get();
// Check if the handler reference is still there
if(handler != null) {
if (Log.isLoggable(Log.TRACE)) {
Log.trace(TAG_LOG, "dispatching message to handler " + handler + "," + message);
}
handler.receiveMessage(message);
}
}
}
// Find the specified handler within the message type handlers
private BusMessageHandler findMessageHandler(Class type, BusMessageHandler handler) {
synchronized(handlersLock) {
WeakReference wrHandler = findWRMessageHandler(type, handler);
if(wrHandler != null) {
return (BusMessageHandler)wrHandler.get();
} else {
return null;
}
}
}
private WeakReference findWRMessageHandler(Class type, BusMessageHandler handler) {
synchronized(handlersLock) {
Vector typeHandlers = (Vector)handlers.get(type);
if(typeHandlers != null) {
Enumeration elements = typeHandlers.elements();
while(elements.hasMoreElements()) {
WeakReference wrHandler = (WeakReference)elements.nextElement();
if(handler == (BusMessageHandler)wrHandler.get()) {
return wrHandler;
}
}
}
return null;
}
}
// Dispatches the messages from the messageQueue
private class MessageQueueRunner implements Runnable {
public void run() {
try {
while (true) {
synchronized(messageQueueLock) {
messageQueueLock.wait();
}
BusMessage message;
while((message = getNextMessage()) != null) {
dispatchMessage(message);
}
}
} catch (Throwable e) {
throw new RuntimeException(e);
}
}
public BusMessage getNextMessage() {
synchronized(messageQueueLock) {
return messageQueue.get();
}
}
}
/**
* Represents a FIFO queue of BusMessage objects. It simply allows to add
* elements and remove them from the list.
*/
private class MessageQueue {
private Vector internalQueue = new Vector();
public BusMessage get() {
if(internalQueue.size() > 0) {
BusMessage result = (BusMessage)internalQueue.elementAt(0);
internalQueue.removeElementAt(0);
return result;
} else {
return null;
}
}
public void add(BusMessage m) {
internalQueue.addElement(m);
}
}
}