kafka Crc32C 源码

kafka Crc32C 代码

文件路径：/clients/src/main/java/org/apache/kafka/common/utils/Crc32C.java

/*
 * 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.kafka.common.utils;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.nio.ByteBuffer;
import java.util.zip.Checksum;

/**
 * A class that can be used to compute the CRC32C (Castagnoli) of a ByteBuffer or array of bytes.
 *
 * We use java.util.zip.CRC32C (introduced in Java 9) if it is available and fallback to PureJavaCrc32C, otherwise.
 * java.util.zip.CRC32C is significantly faster on reasonably modern CPUs as it uses the CRC32 instruction introduced
 * in SSE4.2.
 *
 * NOTE: This class is intended for INTERNAL usage only within Kafka.
 */
public final class Crc32C {

    private static final ChecksumFactory CHECKSUM_FACTORY;

    static {
        if (Java.IS_JAVA9_COMPATIBLE)
            CHECKSUM_FACTORY = new Java9ChecksumFactory();
        else
            CHECKSUM_FACTORY = new PureJavaChecksumFactory();
    }

    private Crc32C() {}

    /**
     * Compute the CRC32C (Castagnoli) of the segment of the byte array given by the specified size and offset
     *
     * @param bytes The bytes to checksum
     * @param offset the offset at which to begin the checksum computation
     * @param size the number of bytes to checksum
     * @return The CRC32C
     */
    public static long compute(byte[] bytes, int offset, int size) {
        Checksum crc = create();
        crc.update(bytes, offset, size);
        return crc.getValue();
    }

    /**
     * Compute the CRC32C (Castagnoli) of a byte buffer from a given offset (relative to the buffer's current position)
     *
     * @param buffer The buffer with the underlying data
     * @param offset The offset relative to the current position
     * @param size The number of bytes beginning from the offset to include
     * @return The CRC32C
     */
    public static long compute(ByteBuffer buffer, int offset, int size) {
        Checksum crc = create();
        Checksums.update(crc, buffer, offset, size);
        return crc.getValue();
    }

    public static Checksum create() {
        return CHECKSUM_FACTORY.create();
    }

    private interface ChecksumFactory {
        Checksum create();
    }

    private static class Java9ChecksumFactory implements ChecksumFactory {
        private static final MethodHandle CONSTRUCTOR;

        static {
            try {
                Class<?> cls = Class.forName("java.util.zip.CRC32C");
                CONSTRUCTOR = MethodHandles.publicLookup().findConstructor(cls, MethodType.methodType(void.class));
            } catch (ReflectiveOperationException e) {
                // Should never happen
                throw new RuntimeException(e);
            }
        }

        @Override
        public Checksum create() {
            try {
                return (Checksum) CONSTRUCTOR.invoke();
            } catch (Throwable throwable) {
                // Should never happen
                throw new RuntimeException(throwable);
            }
        }
    }

    private static class PureJavaChecksumFactory implements ChecksumFactory {
        @Override
        public Checksum create() {
            return new PureJavaCrc32C();
        }
    }
}

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