org.apache.hadoop.util.NativeCrc32.java Source code

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Here is the source code for org.apache.hadoop.util.NativeCrc32.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.util;

import java.nio.ByteBuffer;
import java.util.zip.Checksum;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.fs.ChecksumException;

/**
 * Wrapper around JNI support code to do checksum computation
 * natively.
 */
public class NativeCrc32 implements Checksum {
    static {
        NativeCodeLoader.isNativeCodeLoaded();
    }
    /** the current CRC value, bit-flipped */
    private int crc;
    private final PureJavaCrc32 pureJavaCrc32 = new PureJavaCrc32();
    private final PureJavaCrc32C pureJavaCrc32C = new PureJavaCrc32C();
    private int checksumType = CHECKSUM_CRC32;

    private boolean isAvailable = true;
    // Local benchmarks show that for >= 128 bytes, NativeCrc32 performs
    // better than PureJavaCrc32.
    private static final int SMALL_CHECKSUM = 128;
    private static final Log LOG = LogFactory.getLog(NativeCrc32.class);

    public NativeCrc32(int checksumType) {
        this();
        if (checksumType != CHECKSUM_CRC32 && checksumType != CHECKSUM_CRC32C) {
            throw new IllegalArgumentException("Invalid checksum type");
        }
        this.checksumType = checksumType;
    }

    public NativeCrc32() {
        isAvailable = isAvailable();
        reset();
    }

    /** {@inheritDoc} */
    public long getValue() {
        return (~crc) & 0xffffffffL;
    }

    public void setValue(int crc) {
        this.crc = ~crc;
    }

    /** {@inheritDoc} */
    public void reset() {
        crc = 0xffffffff;
    }

    /**
     * Return true if the JNI-based native CRC extensions are available.
     */
    public static boolean isAvailable() {
        return NativeCodeLoader.isNativeCodeLoaded();
    }

    /**
     * Verify the given buffers of data and checksums, and throw an exception
     * if any checksum is invalid. The buffers given to this function should
     * have their position initially at the start of the data, and their limit
     * set at the end of the data. The position, limit, and mark are not
     * modified.
     * 
     * @param bytesPerSum the chunk size (eg 512 bytes)
     * @param checksumType the DataChecksum type constant
     * @param sums the DirectByteBuffer pointing at the beginning of the
     *             stored checksums
     * @param data the DirectByteBuffer pointing at the beginning of the
     *             data to check
     * @param basePos the position in the file where the data buffer starts 
     * @param fileName the name of the file being verified
     * @throws ChecksumException if there is an invalid checksum
     */
    public static void verifyChunkedSums(int bytesPerSum, int checksumType, ByteBuffer sums, ByteBuffer data,
            String fileName, long basePos) throws ChecksumException {
        nativeVerifyChunkedSums(bytesPerSum, checksumType, sums, sums.position(), data, data.position(),
                data.remaining(), fileName, basePos);
    }

    public void update(int b) {
        byte[] buf = new byte[1];
        buf[0] = (byte) b;
        update(buf, 0, buf.length);
    }

    private void updatePureJava(byte[] buf, int offset, int len) {
        if (checksumType == CHECKSUM_CRC32) {
            pureJavaCrc32.setValueInternal(crc);
            pureJavaCrc32.update(buf, offset, len);
            crc = pureJavaCrc32.getCrcValue();
        } else {
            pureJavaCrc32C.setValueInternal(crc);
            pureJavaCrc32C.update(buf, offset, len);
            crc = pureJavaCrc32C.getCrcValue();
        }
    }

    public void update(byte[] buf, int offset, int len) {
        // To avoid JNI overhead, use native methods only for large checksum chunks.
        if (isAvailable && len >= SMALL_CHECKSUM) {
            try {
                crc = update(crc, buf, offset, len, checksumType);
            } catch (UnsatisfiedLinkError ule) {
                isAvailable = false;
                LOG.warn("Could not find native crc32 libraries," + " falling back to pure java", ule);
                updatePureJava(buf, offset, len);
            }
        } else {
            updatePureJava(buf, offset, len);
        }
    }

    public native int update(int crc, byte[] buf, int offset, int len, int checksumType);

    private static native void nativeVerifyChunkedSums(int bytesPerSum, int checksumType, ByteBuffer sums,
            int sumsOffset, ByteBuffer data, int dataOffset, int dataLength, String fileName, long basePos);

    // Copy the constants over from DataChecksum so that javah will pick them up
    // and make them available in the native code header.
    public static final int CHECKSUM_CRC32 = DataChecksum.CHECKSUM_CRC32;
    public static final int CHECKSUM_CRC32C = DataChecksum.CHECKSUM_CRC32C;
}