/*
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* 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.
*
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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;
}