Package org.apache.hadoop.fs.impl.prefetch

Class BlockManager

java.lang.Object

org.apache.hadoop.fs.impl.prefetch.BlockManager

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

Direct Known Subclasses:

CachingBlockManager

public abstract class BlockManager
extends java.lang.Object
implements java.io.Closeable

Provides read access to the underlying file one block at a time. This class is the simplest form of a BlockManager that does perform prefetching or caching.

Constructor Summary

Constructors

Constructor	Description
BlockManager(BlockData blockData)	Constructs an instance of BlockManager.

Method Summary

Modifier and Type	Method	Description
void	cancelPrefetches()	Requests cancellation of any previously issued prefetch requests.
void	close()
BufferData	get(int blockNumber)	Gets the block having the given blockNumber.
BlockData	getBlockData()	Gets block data information.
abstract int	read(java.nio.ByteBuffer buffer, long startOffset, int size)	Reads into the given buffer size bytes from the underlying file starting at startOffset.
void	release(BufferData data)	Releases resources allocated to the given block.
void	requestCaching(BufferData data)	Requests that the given block should be copied to the cache.
void	requestPrefetch(int blockNumber)	Requests optional prefetching of the given block.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BlockManager

public BlockManager(BlockData blockData)

Constructs an instance of BlockManager.

Parameters:

blockData - information about each block of the underlying file.

Throws:

java.lang.IllegalArgumentException - if blockData is null.

Method Detail

getBlockData

public BlockData getBlockData()

Gets block data information.

Returns:

instance of BlockData.

get

public BufferData get(int blockNumber)
               throws java.io.IOException

Gets the block having the given blockNumber. The entire block is read into memory and returned as a BufferData. The blocks are treated as a limited resource and must be released when one is done reading them.

Parameters:

blockNumber - the number of the block to be read and returned.

Returns:

BufferData having data from the given block.

Throws:

java.io.IOException - if there an error reading the given block.

java.lang.IllegalArgumentException - if blockNumber is negative.

read

public abstract int read(java.nio.ByteBuffer buffer,
                         long startOffset,
                         int size)
                  throws java.io.IOException

Reads into the given buffer size bytes from the underlying file starting at startOffset.

Parameters:

buffer - the buffer to read data in to.

startOffset - the offset at which reading starts.

size - the number bytes to read.

Returns:

number of bytes read.

Throws:

java.io.IOException - if there an error reading the given block.

release

public void release(BufferData data)

Releases resources allocated to the given block.

Parameters:

data - the BufferData to release.

Throws:

java.lang.IllegalArgumentException - if data is null.

requestPrefetch

public void requestPrefetch(int blockNumber)

Requests optional prefetching of the given block.

Parameters:

blockNumber - the id of the block to prefetch.

Throws:

java.lang.IllegalArgumentException - if blockNumber is negative.

cancelPrefetches

public void cancelPrefetches()

Requests cancellation of any previously issued prefetch requests.

requestCaching

public void requestCaching(BufferData data)

Requests that the given block should be copied to the cache. Optional operation.

Parameters:

data - the BufferData instance to optionally cache.

close

public void close()

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable