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The ActiveMQ Message Broker and Client implementations
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/**
 * 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.activemq.transport.nio;

import java.io.EOFException;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.WritableByteChannel;

/**
 * An optimized buffered outputstream for Tcp
 * 
 * @version $Revision: 1.1.1.1 $
 */

public class NIOOutputStream extends OutputStream {

    private static final int BUFFER_SIZE = 8192;

    private final WritableByteChannel out;
    private final byte[] buffer;
    private final ByteBuffer byteBuffer;

    private int count;
    private boolean closed;

    /**
     * Constructor
     * 
     * @param out
     */
    public NIOOutputStream(WritableByteChannel out) {
        this(out, BUFFER_SIZE);
    }

    /**
     * Creates a new buffered output stream to write data to the specified
     * underlying output stream with the specified buffer size.
     * 
     * @param out the underlying output stream.
     * @param size the buffer size.
     * @throws IllegalArgumentException if size <= 0.
     */
    public NIOOutputStream(WritableByteChannel out, int size) {
        this.out = out;
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        buffer = new byte[size];
        byteBuffer = ByteBuffer.wrap(buffer);
    }

    /**
     * write a byte on to the stream
     * 
     * @param b - byte to write
     * @throws IOException
     */
    public void write(int b) throws IOException {
        checkClosed();
        if (availableBufferToWrite() < 1) {
            flush();
        }
        buffer[count++] = (byte)b;
    }

    /**
     * write a byte array to the stream
     * 
     * @param b the byte buffer
     * @param off the offset into the buffer
     * @param len the length of data to write
     * @throws IOException
     */
    public void write(byte b[], int off, int len) throws IOException {
        checkClosed();
        if (availableBufferToWrite() < len) {
            flush();
        }
        if (buffer.length >= len) {
            System.arraycopy(b, off, buffer, count, len);
            count += len;
        } else {
            write(ByteBuffer.wrap(b, off, len));
        }
    }

    /**
     * flush the data to the output stream This doesn't call flush on the
     * underlying outputstream, because Tcp is particularly efficent at doing
     * this itself ....
     * 
     * @throws IOException
     */
    public void flush() throws IOException {
        if (count > 0 && out != null) {
            byteBuffer.position(0);
            byteBuffer.limit(count);
            write(byteBuffer);
            count = 0;
        }
    }

    /**
     * close this stream
     * 
     * @throws IOException
     */
    public void close() throws IOException {
        super.close();
        closed = true;
    }

    /**
     * Checks that the stream has not been closed
     * 
     * @throws IOException
     */
    protected void checkClosed() throws IOException {
        if (closed) {
            throw new EOFException("Cannot write to the stream any more it has already been closed");
        }
    }

    /**
     * @return the amount free space in the buffer
     */
    private int availableBufferToWrite() {
        return buffer.length - count;
    }

    protected void write(ByteBuffer data) throws IOException {
        int remaining = data.remaining();
        int lastRemaining = remaining - 1;
        long delay = 1;
        while (remaining > 0) {

            // We may need to do a little bit of sleeping to avoid a busy loop.
            // Slow down if no data was written out..
            if (remaining == lastRemaining) {
                try {
                    // Use exponential rollback to increase sleep time.
                    Thread.sleep(delay);
                    delay *= 2;
                    if (delay > 1000) {
                        delay = 1000;
                    }
                } catch (InterruptedException e) {
                    throw new InterruptedIOException();
                }
            } else {
                delay = 1;
            }
            lastRemaining = remaining;

            // Since the write is non-blocking, all the data may not have been
            // written.
            out.write(data);
            remaining = data.remaining();
        }
    }

}