141 lines
4.9 KiB
Java
141 lines
4.9 KiB
Java
/*
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* Copyright (c) 1997, 2001, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package sun.rmi.log;
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import java.io.*;
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import sun.rmi.server.MarshalOutputStream;
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import sun.rmi.server.MarshalInputStream;
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/**
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* A LogHandler represents snapshots and update records as serializable
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* objects.
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*
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* This implementation does not know how to create an initial snaphot or
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* apply an update to a snapshot. The client must specifiy these methods
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* via a subclass.
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*
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* @see ReliableLog
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*
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* @author Ann Wollrath
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*/
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public abstract
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class LogHandler {
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/**
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* Creates a LogHandler for a ReliableLog.
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*/
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public LogHandler() {}
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/**
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* Creates and returns the initial state of data structure that needs
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* to be stably stored. This method is called when a ReliableLog is
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* created.
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* @return the initial state
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* @exception Exception can raise any exception
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*/
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public abstract
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Object initialSnapshot() throws Exception;
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/**
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* Writes the snapshot object to a stream. This callback is
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* invoked when the client calls the snaphot method of ReliableLog.
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* @param out the output stream
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* @param value the snapshot
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* @exception Exception can raise any exception
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*/
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public
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void snapshot(OutputStream out, Object value) throws Exception {
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MarshalOutputStream s = new MarshalOutputStream(out);
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s.writeObject(value);
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s.flush();
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}
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/**
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* Read the snapshot object from a stream and returns the snapshot.
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* This callback is invoked when the client calls the recover method
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* of ReliableLog.
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* @param in the input stream
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* @return the state (snapshot)
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* @exception Exception can raise any exception
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*/
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public
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Object recover(InputStream in) throws Exception {
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MarshalInputStream s = new MarshalInputStream(in);
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return s.readObject();
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}
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/**
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* Writes the representation (a serializable object) of an update
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* to a stream. This callback is invoked when the client calls the
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* update method of ReliableLog.
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* @param out the output stream
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* @param value the snapshot
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* @exception Exception can raise any exception
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*/
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public
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void writeUpdate(LogOutputStream out, Object value) throws Exception {
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MarshalOutputStream s = new MarshalOutputStream(out);
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s.writeObject(value);
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s.flush();
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}
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/**
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* Reads a stably logged update (a serializable object) from a
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* stream. This callback is invoked during recovery, once for
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* every record in the log. After reading the update, this method
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* invokes the applyUpdate (abstract) method in order to obtain
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* the new snapshot value. It then returns the new snapshot.
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*
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* @param in the input stream
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* @param state the current state
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* @return the new state
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* @exception Exception can raise any exception
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*/
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public
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Object readUpdate(LogInputStream in, Object state) throws Exception {
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MarshalInputStream s = new MarshalInputStream(in);
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return applyUpdate(s.readObject(), state);
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}
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/**
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* Reads a stably logged update (a serializable object) from a stream.
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* This callback is invoked during recovery, once for every record in the
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* log. After reading the update, this method is invoked in order to
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* obtain the new snapshot value. The method should apply the update
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* object to the current state <code>state</code> and return the new
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* state (the new snapshot value).
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* @param update the update object
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* @param state the current state
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* @return the new state
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* @exception Exception can raise any exception
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*/
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public abstract
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Object applyUpdate(Object update, Object state) throws Exception;
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}
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