alluxio.worker.block

Class UnderFileSystemBlockReader

java.lang.Object

alluxio.worker.block.io.BlockClient

alluxio.worker.block.io.BlockReader

alluxio.worker.block.UnderFileSystemBlockReader

All Implemented Interfaces:

Closeable, AutoCloseable

@NotThreadSafe
public final class UnderFileSystemBlockReader
extends BlockReader

This class implements a BlockReader to read a block directly from UFS, and optionally cache the block to the Alluxio worker if the whole block it is read.

Nested Class Summary

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

BlockClient.Type

Method Summary

Modifier and Type	Method and Description
void	close() Closes the block reader.
static UnderFileSystemBlockReader	create(UnderFileSystemBlockMeta blockMeta, long offset, boolean positionShort, LocalBlockStore localBlockStore, UfsManager.UfsClient ufsClient, UfsInputStreamCache ufsInStreamCache, com.codahale.metrics.Counter ufsBytesRead, com.codahale.metrics.Meter ufsBytesReadThroughput) Creates an instance of UnderFileSystemBlockReader and initializes it with a reading offset.
ReadableByteChannel	getChannel() Returns a readable byte channel of the block.
long	getLength() Gets the length of the block in bytes.
String	getLocation()
boolean	isClosed()
ByteBuffer	read(long offset, long length) Reads data from the block.
int	transferTo(io.netty.buffer.ByteBuf buf) This interface is supposed to be used for sequence block reads.

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

toString

Methods inherited from class java.lang.Object

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

Method Detail

create

public static UnderFileSystemBlockReader create(UnderFileSystemBlockMeta blockMeta,
                                                long offset,
                                                boolean positionShort,
                                                LocalBlockStore localBlockStore,
                                                UfsManager.UfsClient ufsClient,
                                                UfsInputStreamCache ufsInStreamCache,
                                                com.codahale.metrics.Counter ufsBytesRead,
                                                com.codahale.metrics.Meter ufsBytesReadThroughput)
                                         throws IOException

Creates an instance of UnderFileSystemBlockReader and initializes it with a reading offset.

Parameters:

blockMeta - the block meta

offset - the position within the block to start the read

localBlockStore - the Local block store

ufsClient - the manager of ufs

positionShort - whether the client op is a positioned read to a small buffer

ufsInStreamCache - the UFS in stream cache

ufsBytesRead - counter metric to track ufs bytes read

ufsBytesReadThroughput - meter metric to track bytes read throughput

Returns:

the block reader

Throws:

IOException

getChannel

public ReadableByteChannel getChannel()

Description copied from class: BlockReader

Returns a readable byte channel of the block.

Specified by:

getChannel in class BlockReader

Returns:

channel

getLength

public long getLength()

Description copied from class: BlockReader

Gets the length of the block in bytes.

Specified by:

getLength in class BlockReader

Returns:

the length of the block in bytes

read

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

Description copied from class: BlockReader

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 BlockReader.transferTo(ByteBuf) instead. It is then the caller's responsibility to de-allocate the buffer.

Specified by:

read in class BlockReader

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

transferTo

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

This interface is supposed to be used for sequence block reads.

Specified by:

transferTo in class BlockReader

Parameters:

buf - the byte buffer

Returns:

the number of bytes read, -1 if it reaches EOF and none was read

Throws:

IOException

close

public void close()
           throws IOException

Closes the block reader. After this, this block reader should not be used anymore. This is recommended to be called after the client finishes reading the block. It is usually triggered when the client unlocks the block.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Overrides:

close in class BlockClient

Throws:

IOException

isClosed

public boolean isClosed()

Specified by:

isClosed in class BlockReader

Returns:

true if this reader is closed

getLocation

public String getLocation()

Specified by:

getLocation in class BlockReader

Returns:

an informational string of the location the reader is reading from