org.apache.hadoop.fs.ByteBufferUtil.java Source code

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Here is the source code for org.apache.hadoop.fs.ByteBufferUtil.java

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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.hadoop.fs;

import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.ByteBufferPool;

import com.google.common.base.Preconditions;

@InterfaceAudience.Private
@InterfaceStability.Evolving
public final class ByteBufferUtil {

    /**
     * Determine if a stream can do a byte buffer read via read(ByteBuffer buf)
     */
    private static boolean streamHasByteBufferRead(InputStream stream) {
        if (!(stream instanceof ByteBufferReadable)) {
            return false;
        }
        if (!(stream instanceof FSDataInputStream)) {
            return true;
        }
        return ((FSDataInputStream) stream).getWrappedStream() instanceof ByteBufferReadable;
    }

    /**
     * Perform a fallback read.
     */
    public static ByteBuffer fallbackRead(InputStream stream, ByteBufferPool bufferPool, int maxLength)
            throws IOException {
        if (bufferPool == null) {
            throw new UnsupportedOperationException("zero-copy reads "
                    + "were not available, and you did not provide a fallback " + "ByteBufferPool.");
        }
        boolean useDirect = streamHasByteBufferRead(stream);
        ByteBuffer buffer = bufferPool.getBuffer(useDirect, maxLength);
        if (buffer == null) {
            throw new UnsupportedOperationException(
                    "zero-copy reads " + "were not available, and the ByteBufferPool did not provide " + "us with "
                            + (useDirect ? "a direct" : "an indirect") + "buffer.");
        }
        Preconditions.checkState(buffer.capacity() > 0);
        Preconditions.checkState(buffer.isDirect() == useDirect);
        maxLength = Math.min(maxLength, buffer.capacity());
        boolean success = false;
        try {
            if (useDirect) {
                buffer.clear();
                buffer.limit(maxLength);
                ByteBufferReadable readable = (ByteBufferReadable) stream;
                int totalRead = 0;
                while (true) {
                    if (totalRead >= maxLength) {
                        success = true;
                        break;
                    }
                    int nRead = readable.read(buffer);
                    if (nRead < 0) {
                        if (totalRead > 0) {
                            success = true;
                        }
                        break;
                    }
                    totalRead += nRead;
                }
                buffer.flip();
            } else {
                buffer.clear();
                int nRead = stream.read(buffer.array(), buffer.arrayOffset(), maxLength);
                if (nRead >= 0) {
                    buffer.limit(nRead);
                    success = true;
                }
            }
        } finally {
            if (!success) {
                // If we got an error while reading, or if we are at EOF, we 
                // don't need the buffer any more.  We can give it back to the
                // bufferPool.
                bufferPool.putBuffer(buffer);
                buffer = null;
            }
        }
        return buffer;
    }
}