hadoop BlockManager 源码
haddop BlockManager 代码
文件路径:/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/BlockManager.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.impl.prefetch;
import java.io.Closeable;
import java.io.IOException;
import java.nio.ByteBuffer;
import static org.apache.hadoop.fs.impl.prefetch.Validate.checkNotNegative;
import static org.apache.hadoop.fs.impl.prefetch.Validate.checkNotNull;
/**
* Provides read access to the underlying file one block at a time.
*
* This class is the simplest form of a {@code BlockManager} that does
* perform prefetching or caching.
*/
public abstract class BlockManager implements Closeable {
/**
* Information about each block of the underlying file.
*/
private final BlockData blockData;
/**
* Constructs an instance of {@code BlockManager}.
*
* @param blockData information about each block of the underlying file.
*
* @throws IllegalArgumentException if blockData is null.
*/
public BlockManager(BlockData blockData) {
checkNotNull(blockData, "blockData");
this.blockData = blockData;
}
/**
* Gets block data information.
*
* @return instance of {@code BlockData}.
*/
public BlockData getBlockData() {
return blockData;
}
/**
* Gets the block having the given {@code blockNumber}.
*
* The entire block is read into memory and returned as a {@code BufferData}.
* The blocks are treated as a limited resource and must be released when
* one is done reading them.
*
* @param blockNumber the number of the block to be read and returned.
* @return {@code BufferData} having data from the given block.
*
* @throws IOException if there an error reading the given block.
* @throws IllegalArgumentException if blockNumber is negative.
*/
public BufferData get(int blockNumber) throws IOException {
checkNotNegative(blockNumber, "blockNumber");
int size = blockData.getSize(blockNumber);
ByteBuffer buffer = ByteBuffer.allocate(size);
long startOffset = blockData.getStartOffset(blockNumber);
read(buffer, startOffset, size);
buffer.flip();
return new BufferData(blockNumber, buffer);
}
/**
* Reads into the given {@code buffer} {@code size} bytes from the underlying file
* starting at {@code startOffset}.
*
* @param buffer the buffer to read data in to.
* @param startOffset the offset at which reading starts.
* @param size the number bytes to read.
* @return number of bytes read.
* @throws IOException if there an error reading the given block.
*/
public abstract int read(ByteBuffer buffer, long startOffset, int size) throws IOException;
/**
* Releases resources allocated to the given block.
*
* @param data the {@code BufferData} to release.
*
* @throws IllegalArgumentException if data is null.
*/
public void release(BufferData data) {
checkNotNull(data, "data");
// Do nothing because we allocate a new buffer each time.
}
/**
* Requests optional prefetching of the given block.
*
* @param blockNumber the id of the block to prefetch.
*
* @throws IllegalArgumentException if blockNumber is negative.
*/
public void requestPrefetch(int blockNumber) {
checkNotNegative(blockNumber, "blockNumber");
// Do nothing because we do not support prefetches.
}
/**
* Requests cancellation of any previously issued prefetch requests.
*/
public void cancelPrefetches() {
// Do nothing because we do not support prefetches.
}
/**
* Requests that the given block should be copied to the cache. Optional operation.
*
* @param data the {@code BufferData} instance to optionally cache.
*/
public void requestCaching(BufferData data) {
// Do nothing because we do not support caching.
}
@Override
public void close() {
}
}
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