alluxio.worker.block.io

Class BlockReader

java.lang.Object

alluxio.worker.block.io.BlockClient

alluxio.worker.block.io.BlockReader

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

DelegatingBlockReader, LocalFileBlockReader, PagedBlockReader, PagedUfsBlockReader, RemoteBlockReader, UnderFileSystemBlockReader

public abstract class BlockReader
extends BlockClient

An abstract reader class to access the data of a block stored in managed storage.

This class does not provide thread-safety.

Nested Class Summary

Nested classes/interfaces inherited from class alluxio.worker.block.io.BlockClient

BlockClient.Type

Constructor Summary

Constructors

Constructor and Description
BlockReader() Default constructor for the abstract reader implementations.

Method Summary

Modifier and Type	Method and Description
abstract ReadableByteChannel	getChannel() Returns a readable byte channel of the block.
abstract long	getLength() Gets the length of the block in bytes.
abstract String	getLocation()
abstract boolean	isClosed()
abstract ByteBuffer	read(long offset, long length) Reads data from the block.
abstract int	transferTo(io.netty.buffer.ByteBuf buf) Transfers data (up to buf.writableBytes()) from this reader to the buffer.

Methods inherited from class alluxio.worker.block.io.BlockClient

close, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

BlockReader

public BlockReader()

Default constructor for the abstract reader implementations.

Method Detail

read

public abstract ByteBuffer read(long offset,
                                long length)
                         throws IOException

Reads data from the block.

Implementation Note

Since this method needs to allocate a buffer inside its implementation, it must not choose a ByteBuffer that needs any kind of explicit de-allocation, e.g. a pooled buffer, because the caller has no means of knowing how and when to properly deallocate the returned buffer.
If explicit de-allocation is desired, use an externally allocated ByteBuf and call transferTo(ByteBuf) instead. It is then the caller's responsibility to de-allocate the buffer.

Parameters:

offset - the offset from starting of the block file in bytes

length - the length of data to read in bytes. If offset + length exceeds the block size, the part of data from offset to the end of block is returned.

Returns:

ByteBuffer the data that was read, empty buffer if offset is at the end of block

Throws:

IOException

getLength

public abstract long getLength()

Gets the length of the block in bytes.

Returns:

the length of the block in bytes

getChannel

public abstract ReadableByteChannel getChannel()

Returns a readable byte channel of the block.

Returns:

channel

transferTo

public abstract int transferTo(io.netty.buffer.ByteBuf buf)
                        throws IOException

Transfers data (up to buf.writableBytes()) from this reader to the buffer.

Parameters:

buf - the byte buffer

Returns:

the number of bytes transferred, -1 if the end of the block is reached

Throws:

IOException

isClosed

public abstract boolean isClosed()

Returns:

true if this reader is closed

getLocation

public abstract String getLocation()

Returns:

an informational string of the location the reader is reading from