hadoop HasEnhancedByteBufferAccess 源码
haddop HasEnhancedByteBufferAccess 代码
文件路径:/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/HasEnhancedByteBufferAccess.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.hadoop.fs;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.EnumSet;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.ByteBufferPool;
/**
* FSDataInputStreams implement this interface to provide enhanced
* byte buffer access. Usually this takes the form of mmap support.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public interface HasEnhancedByteBufferAccess {
/**
* Get a ByteBuffer containing file data.
*
* This ByteBuffer may come from the stream itself, via a call like mmap,
* or it may come from the ByteBufferFactory which is passed in as an
* argument.
*
* @param factory
* If this is non-null, it will be used to create a fallback
* ByteBuffer when the stream itself cannot create one.
* @param maxLength
* The maximum length of buffer to return. We may return a buffer
* which is shorter than this.
* @param opts
* Options to use when reading.
*
* @return
* We will always return an empty buffer if maxLength was 0,
* whether or not we are at EOF.
* If maxLength > 0, we will return null if the stream
* has reached EOF.
* Otherwise, we will return a ByteBuffer containing at least one
* byte. You must free this ByteBuffer when you are done with it
* by calling releaseBuffer on it. The buffer will continue to be
* readable until it is released in this manner. However, the
* input stream's close method may warn about unclosed buffers.
* @throws IOException if there was an error reading.
* @throws UnsupportedOperationException if factory was null,
* and we needed an external byte buffer.
* @throws UnsupportedOperationException will never be thrown
* unless the factory argument is null.
*
*/
public ByteBuffer read(ByteBufferPool factory, int maxLength,
EnumSet<ReadOption> opts)
throws IOException, UnsupportedOperationException;
/**
* Release a ByteBuffer which was created by the enhanced ByteBuffer read
* function. You must not continue using the ByteBuffer after calling this
* function.
*
* @param buffer
* The ByteBuffer to release.
*/
public void releaseBuffer(ByteBuffer buffer);
}
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