/*

 * Copyright (c) 1997, 2001, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package sun.rmi.log;

import java.io.*;

import sun.rmi.server.MarshalOutputStream;

import sun.rmi.server.MarshalInputStream;

/**

 * A LogHandler represents snapshots and update records as serializable

 * objects.

 *

 * This implementation does not know how to create an initial snaphot or

 * apply an update to a snapshot.  The client must specifiy these methods

 * via a subclass.

 *

 * @see ReliableLog

 *

 * @author Ann Wollrath

 */

public abstract

class LogHandler {

    /**

     * Creates a LogHandler for a ReliableLog.

     */

    public LogHandler() {}

    /**

     * Creates and returns the initial state of data structure that needs

     * to be stably stored. This method is called when a ReliableLog is

     * created.

     * @return the initial state

     * @exception Exception can raise any exception

     */

    public abstract

    Object initialSnapshot() throws Exception;

    /**

     * Writes the snapshot object to a stream.  This callback is

     * invoked when the client calls the snaphot method of ReliableLog.

     * @param out the output stream

     * @param value the snapshot

     * @exception Exception can raise any exception

     */

    public

    void snapshot(OutputStream out, Object value) throws Exception {

        MarshalOutputStream s = new MarshalOutputStream(out);

        s.writeObject(value);

        s.flush();

    }

    /**

     * Read the snapshot object from a stream and returns the snapshot.

     * This callback is invoked when the client calls the recover method

     * of ReliableLog.

     * @param in the input stream

     * @return the state (snapshot)

     * @exception Exception can raise any exception

     */

    public

    Object recover(InputStream in) throws Exception {

        MarshalInputStream s = new MarshalInputStream(in);

        return s.readObject();

    }

    /**

     * Writes the representation (a serializable object) of an update

     * to a stream.  This callback is invoked when the client calls the

     * update method of ReliableLog.

     * @param out the output stream

     * @param value the snapshot

     * @exception Exception can raise any exception

     */

    public

    void writeUpdate(LogOutputStream out, Object value) throws Exception {

        MarshalOutputStream s = new MarshalOutputStream(out);

        s.writeObject(value);

        s.flush();

    }

    /**

     * Reads a stably logged update (a serializable object) from a

     * stream.  This callback is invoked during recovery, once for

     * every record in the log.  After reading the update, this method

     * invokes the applyUpdate (abstract) method in order to obtain

     * the new snapshot value.  It then returns the new snapshot.

     *

     * @param in the input stream

     * @param state the current state

     * @return the new state

     * @exception Exception can raise any exception

     */

    public

    Object readUpdate(LogInputStream in, Object state) throws Exception {

        MarshalInputStream  s = new MarshalInputStream(in);

        return applyUpdate(s.readObject(), state);

    }

    /**

     * Reads a stably logged update (a serializable object) from a stream.

     * This callback is invoked during recovery, once for every record in the

     * log.  After reading the update, this method is invoked in order to

     * obtain the new snapshot value.  The method should apply the update

     * object to the current state <code>state</code> and return the new

     * state (the new snapshot value).

     * @param update the update object

     * @param state the current state

     * @return the new state

     * @exception Exception can raise any exception

     */

    public abstract

    Object applyUpdate(Object update, Object state) throws Exception;

}