abstractmessenger.java

jxta_src_2.41b jxta 2.41b 最新版源码 from www.jxta.org

/*
 *
 * $Id: AbstractMessenger.java,v 1.6 2006/01/05 18:28:43 bondolo Exp $
 *
 * Copyright (c) 2004 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *       Sun Microsystems, Inc. for Project JXTA."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA"
 *    must not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact Project JXTA at http://www.jxta.org.
 *
 * 5. Products derived from this software may not be called "JXTA",
 *    nor may "JXTA" appear in their name, without prior written
 *    permission of Sun.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 *
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of Project JXTA.  For more
 * information on Project JXTA, please see
 * <http://www.jxta.org/>.
 *
 * This license is based on the BSD license adopted by the Apache Foundation.
 */

package net.jxta.endpoint;

import java.io.IOException;

import java.io.InterruptedIOException;

import net.jxta.util.AbstractSimpleSelectable;
import net.jxta.util.SimpleSelectable;

/**
 * An AbstractMessenger is used to implement messengers (for example, by transport modules).
 * It supplies the convenience, bw compatible, obvious, or otherwise rarely changed methods.
 * Many method cannot be overloaded in order to ensure standard behaviour.
 * The rest is left to implementations.
 *
 * @see net.jxta.endpoint.EndpointService
 * @see net.jxta.endpoint.EndpointAddress
 * @see net.jxta.endpoint.Message
 **/

public abstract class AbstractMessenger extends AbstractSimpleSelectable implements Messenger {
    
    /**
     * The default Maximum Transmission Unit. Currently it is not enforced but at least
     * that much can always be sent. All messengers getMTU method return this.
     **/
    protected static final long DEFAULT_MTU = 65536L;

    /**
     * The destination address of messages sent on this messenger.
     * This member is protected because some transport messengers believe in reading it.
     * FIXME - [e-mail] 20040413: fix transports.
     **/
    protected final EndpointAddress dstAddress;

    /**
     * The stateLock that we share with the implementation.
     * This permits to implement waitState in a totally generic way: waitState depends only on the lock
     * (provided at construction), and on getState(), supplied by the implementation.
     **/
    private Object stateLock;

    /**
     * Create a new abstract messenger.
     *
     * Warning: This class needs to know the object on which to waitState must synchronize. It is generally impossible
     * to pass it at construction because it is not yet constructed. Instead implementations MUST call {@link #setStateLock}
     * from their constructor.
     *
     * @param dest who messages should be addressed to
     **/
    public AbstractMessenger( EndpointAddress dest ) {
        dstAddress = (EndpointAddress) dest.clone();
    }

    /**
     *  {@inheritDoc}
     *
     *  <p/>A simple implementation for debugging. Don't depend upon this format.
     **/
    public String toString() {
        return super.toString() + "{" + dstAddress.toString() +"}";
    }
    
    /**
     * Specifies the object on which waitState must synchronize.
     *
     * @param stateLock The object on which waitState must synchronize. This has to be the object that gets notified when the
     * implementation changes its state. Changing state is defined as "any operation that causes the result of the
     * <code>getState</code> method to change". Implementations that use the MessengerState state machine should typically use the
     * MessengerState object as their state lock, but it is not assumed.
     **/
    protected void setStateLock(Object stateLock) {
        this.stateLock = stateLock;
    }

    /*
     * Messenger methods implementations.
     */

    /**
     * {@inheritDoc}
     *
     * <p/> This is here for backward compatibility reasons.  The notion of long term unemployment still exists, but is no-longer part
     * of the API.  Self closing for unemployment is now a built-in feature of messengers.
     **/
    public final boolean isIdle() {
        return false;
    }
    
    /**
     * {@inheritDoc}
     **/
    public final boolean isSynchronous() {
        return false;
    }

    /**
     * {@inheritDoc}
     **/
    public EndpointAddress getDestinationAddress() {
        return (EndpointAddress) dstAddress.clone();
    }

    /**
     * {@inheritDoc}
     **/
    public EndpointAddress getDestinationAddressObject() {
        return dstAddress;
    }

    /**
     * {@inheritDoc}
     **/
    public long getMTU() {
        return DEFAULT_MTU;
    }

    /**
     * {@inheritDoc}
     *
     * <p/> This is a minimal implementation. It may not detect closure
     * initiated by the other side unless the messenger was actually used
     * since. A more accurate (but not mandatory implementation) would
     * actually go and check the underlying connection, if relevant...unless
     * breakage initiated by the other side is actually reported asynchronously
     * when it happens. Breakage detection from the other side need not
     * be reported atomically with its occurence. This not very important
     * since we canonicalize transport messengers and so do not need to
     * aggressively collect closed ones. When not used, messengers die by themselves.
     *
     **/
    public boolean isClosed() {
        return ((getState() & USABLE) == 0);
    }
    

    /**
     * {@inheritDoc}
     **/
    public final void flush() throws IOException {
        int currentState = 0;
        try {
            currentState = waitState(IDLE, 0);
        } catch(InterruptedException ie) {
            InterruptedIOException iio = new InterruptedIOException();
            iio.initCause(ie);
            throw iio;
        }
        if ((currentState & (CLOSED | USABLE)) != 0) {
            return;
        }
        throw new IOException("Messenger was unexpectedly closed.");
    }

    /**
     * {@inheritDoc}
     **/
    public final boolean sendMessage( Message msg ) throws IOException {
        return sendMessage( msg, null, null );
    }

    /**
     * {@inheritDoc}
     *
     * @deprecated Implements deprecated method. Actual support only provided by channels.
     **/
    public void sendMessage(Message msg, String service, String serviceParam, OutgoingMessageEventListener listener) {
        throw new UnsupportedOperationException("This legacy method is not supported by this messenger.");
    }

    /**
     * {@inheritDoc}
     **/
    public final boolean sendMessage( Message msg, String rService, String rServiceParam ) throws IOException {

        // We have to retrieve the failure from the message and throw it if its an IOException, this is what the API
        // says that this method does.

        if (sendMessageN(msg, rService, rServiceParam)) {
            return true;
        }

        Object failed = msg.getMessageProperty(Messenger.class);
        if ((failed == null) || !(failed instanceof OutgoingMessageEvent)) {
            // huh ?
            return false;
        }

        Throwable t = ((OutgoingMessageEvent) failed).getFailure();
        if (t == null) {
            // Must be saturation, then. (No throw for that).
            return false;
        }

        // Now see how we can manage to throw it.
        if (t instanceof IOException) {
            throw (IOException) t;
        }
        if (t instanceof RuntimeException) {
            throw (RuntimeException) t;
        }
        if (t instanceof Error) {
            throw (Error) t;
        }
        
        IOException failure = new IOException( "Failure sending message" );
        failure.initCause( t );
        
        throw failure;
    }

    /**
     * {@inheritDoc}
     *
     * <p/> This method synchronizes on the lock object supplied at construction.
     **/
    public final int waitState(int wantedStates, long timeout) throws InterruptedException {
        
        synchronized(stateLock) {

            if (timeout == 0) {
                while ((wantedStates & getState()) == 0) {
                    stateLock.wait();
                }
                return getState();
            }

            if (timeout < 0 ) {
                stateLock.wait(timeout); // let it throw the appropriate error.
            }

            long start = System.currentTimeMillis();
            long end = start + timeout;
            if( end < start ) {
                end = Long.MAX_VALUE;
            }
            long left = end - start;
            while ((left > 0) && (wantedStates & getState()) == 0) {

                stateLock.wait(left);

                left = end - System.currentTimeMillis();
            }
            return getState();
        }
    }

    /*
     * SimpleSelectable implementation.
     */

    /**
     * Implements a default for all AbstractMessengers: mirror the event to our selectors. This is what is needed by all the
     * known AbstractMessengers that register themselves somewhere. (That is ChannelMessengers).
     * FIXME - [e-mail] 20040413: Not sure that this is the best default.
     *
     * @param changedObject Ignored.
     **/
    public void itemChanged(SimpleSelectable changedObject) {
        notifyChange();
    }
}