/*

 * Copyright (c) 1997, 2008, 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * The Original Code is HAT. The Initial Developer of the

 * Original Code is Bill Foote, with contributions from others

 * at JavaSoft/Sun.

 */

package com.sun.tools.hat.internal.parser;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.MappedByteBuffer;

import java.nio.channels.FileChannel;

/**

 * Implementation of ReadBuffer using mapped file buffer

 *

 * @author A. Sundararajan

 */

class MappedReadBuffer implements ReadBuffer {

    private MappedByteBuffer buf;

    MappedReadBuffer(MappedByteBuffer buf) {

        this.buf = buf;

    }

    // factory method to create correct ReadBuffer for a given file

    static ReadBuffer create(RandomAccessFile file) throws IOException {

        FileChannel ch = file.getChannel();

        long size = ch.size();

        // if file size is more than 2 GB and when file mapping is

        // configured (default), use mapped file reader

        if (canUseFileMap() && (size <= Integer.MAX_VALUE)) {

            MappedByteBuffer buf;

            try {

                buf = ch.map(FileChannel.MapMode.READ_ONLY, 0, size);

                ch.close();

                return new MappedReadBuffer(buf);

            } catch (IOException exp) {

                exp.printStackTrace();

                System.err.println("File mapping failed, will use direct read");

                // fall through

            }

        } // else fall through

        return new FileReadBuffer(file);

    }

    private static boolean canUseFileMap() {

        // set jhat.disableFileMap to any value other than "false"

        // to disable file mapping

        String prop = System.getProperty("jhat.disableFileMap");

        return prop == null || prop.equals("false");

    }

    private void seek(long pos) throws IOException {

        assert pos <= Integer.MAX_VALUE :  "position overflow";

        buf.position((int)pos);

    }

    public synchronized void get(long pos, byte[] res) throws IOException {

        seek(pos);

        buf.get(res);

    }

    public synchronized char getChar(long pos) throws IOException {

        seek(pos);

        return buf.getChar();

    }

    public synchronized byte getByte(long pos) throws IOException {

        seek(pos);

        return buf.get();

    }

    public synchronized short getShort(long pos) throws IOException {

        seek(pos);

        return buf.getShort();

    }

    public synchronized int getInt(long pos) throws IOException {

        seek(pos);

        return buf.getInt();

    }

    public synchronized long getLong(long pos) throws IOException {

        seek(pos);

        return buf.getLong();

    }

}