org.apache.hadoop.io.BufferedByteInputStream.java Source code

Introduction

Here is the source code for org.apache.hadoop.io.BufferedByteInputStream.java

Source

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.io;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * BufferedByteInputStream uses an underlying in-memory staging buffer for
 * reading bytes from the underlying input stream. The actual reading is done
 * by a separate thread.
 */
public class BufferedByteInputStream extends InputStream {

    static final Log LOG = LogFactory.getLog(BufferedByteInputStream.class.getName());

    // staging buffer used to store bytes read from underlying stream
    private final BufferedByteInputOutput buffer;

    // reader thread that reads bytes from underlying stream
    // and writes to the buffer
    private final ReadThread readThread;

    // actual input stream to read from
    private final InputStream underlyingInputStream;

    private boolean closed = false;

    /**
     * Wrap given input stream with BufferedByteInputOutput.
     * This is the only way to instantiate the buffered input stream.
     * @param is underlying input stream
     * @param bufferSize size of the in memory buffer
     * @param readBufferSize size of the buffer used for reading from is
     */
    public static DataInputStream wrapInputStream(InputStream is, int bufferSize, int readBufferSize) {
        // wrapping BufferedByteInputStream in BufferedInputStream decreases
        // pressure on BBIS internal locks, and we read from the BBIS in
        // bigger chunks
        return new DataInputStream(
                new BufferedInputStream(new BufferedByteInputStream(is, bufferSize, readBufferSize)));
    }

    /**
     * Construct BuffredByteInputStream
     * @param is underlying input stream
     * @param bufferSize size of the in-memory buffer
     * @param readBufferSize size of the transfer chunks 
     *        (from input stream to staging buffer)
     */
    private BufferedByteInputStream(InputStream is, int bufferSize, int readBufferSize) {
        buffer = new BufferedByteInputOutput(bufferSize);
        readThread = new ReadThread(is, buffer, readBufferSize);
        readThread.setDaemon(true);
        readThread.start();
        underlyingInputStream = is;
    }

    // override InputStream methods
    // each of the calls will fail after the stream is closed
    // after reading all bytes available in the buffer!

    public int read() throws IOException {
        return checkOutput(buffer.read());
    }

    public int read(byte[] buf) throws IOException {
        return checkOutput(buffer.read(buf, 0, buf.length));
    }

    public int read(byte[] buf, int off, int len) throws IOException {
        return checkOutput(buffer.read(buf, off, len));
    }

    /**
     * How many bytes are available in the buffer.
     * After closing this call will fail.
     */
    public int available() throws IOException {
        checkOutput(-1);
        return buffer.available();
    }

    /**
     * Close the input stream. Joins the thread and
     * closes the underlying input stream. Can be
     * called multiple times.
     */
    public void close() throws IOException {
        // multiple close should return with no errors
        // readThread will close underlying buffer
        readThread.close();
        try {
            readThread.join();
        } catch (InterruptedException e) {
            throw new IOException(e);
        }
    }

    /////////////////////////////////////

    /**
     * Check if the read thread died, if so, throw an exception.
     */
    private int checkOutput(int readBytes) throws IOException {
        if (readBytes > -1) {
            return readBytes;
        }
        if (closed) {
            throw new IOException("The stream has been closed");
        }
        if (readThread.error != null) {
            throw new IOException(readThread.error.getMessage());
        }
        return readBytes;
    }

    /**
     * Reader thread which will copy bytes from the underlying input stream
     * to the byte buffer.
     */
    private class ReadThread extends Thread implements Runnable {

        private final InputStream is;
        private final BufferedByteInputOutput buffer;
        private final int readBufferSize;

        volatile Throwable error = null;

        ReadThread(InputStream is, BufferedByteInputOutput os, int readBufferSize) {
            this.buffer = os;
            this.is = is;
            this.readBufferSize = readBufferSize;
        }

        /** 
         * Close input stream.
         * Closes the buffer and underlying input stream;
         */
        void close() throws IOException {
            closed = true;
            buffer.close();
            is.close();
        }

        public void run() {
            byte[] buf = new byte[readBufferSize];
            int bytesRead;
            try {
                while (((bytesRead = is.read(buf)) > 0)) {
                    buffer.write(buf, 0, bytesRead);
                }
            } catch (Exception e) {
                // after closing we might get an error here
                // but we can ignore it
                if (!closed) {
                    error = e;
                    LOG.warn("Exception", e);
                }
            } finally {
                // close buffer and input stream
                buffer.close();
                try {
                    is.close();
                } catch (IOException e) {
                    error = e;
                    LOG.error("Exception when closing underlying input stream", e);
                }
            }
        }
    }
}