com.bigdata.io

Class FileChannelUtility

java.lang.Object

com.bigdata.io.FileChannelUtility

public class FileChannelUtility
extends Object

A helper class for operations on FileChannels.

Author:

Bryan Thompson

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FileChannelUtility.AsyncTransfer The AsyncTransfer class encapsulates the state required to make asynchronous transfer requests.
static interface	FileChannelUtility.IAsyncOpener Define interface to support callback from readAllAsync
static class	FileChannelUtility.ReopenerInputStream An InputStream implementation that utilizes the resilient readAll method of this class

Constructor Summary

Constructors

Constructor and Description
FileChannelUtility()

Method Summary

Methods

Modifier and Type	Method and Description
static int	readAll(FileChannel channel, ByteBuffer src, long pos) Deprecated. by readAll(IReopenChannel, ByteBuffer, long) which handles transparent re-opening of the store in order to complete the read operation.
static int	readAll(IReopenChannel<FileChannel> opener, ByteBuffer src, long pos) Reads Buffer.remaining() bytes into the caller's ByteBuffer from the channel starting at offset pos.
static long	readAllAsync(FileChannelUtility.IAsyncOpener opener, List<FileChannelUtility.AsyncTransfer> transfers) readAllAsync will make repeated attempts to read data into the transfer buffers defined in the List of AsyncTransfer instances.
static int	transferAll(FileChannel sourceChannel, long fromPosition, long count, RandomAccessFile out, long toPosition) FileChannel to FileChannel transfer of count bytes from the sourceChannel starting at the fromPosition onto the out file starting at its current position.
static int	writeAll(FileChannel channel, ByteBuffer data, long pos) Deprecated. by writeAll(IReopenChannel, ByteBuffer, long)
static int	writeAll(IReopenChannel<FileChannel> opener, ByteBuffer data, long pos) Write bytes in data from the position to the limit on the channel starting at pos.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileChannelUtility

public FileChannelUtility()

Method Detail

readAll

public static int readAll(FileChannel channel,
          ByteBuffer src,
          long pos)
                   throws IOException

Deprecated. by readAll(IReopenChannel, ByteBuffer, long) which handles transparent re-opening of the store in order to complete the read operation.

Reads Buffer.remaining() bytes into the caller's ByteBuffer from the channel starting at offset pos. The position of the ByteBuffer is advanced to the limit. The offset of the channel is NOT modified as a side-effect.

This handles partial reads by reading until nbytes bytes have been transferred.

Parameters:

channel - The source FileChannel.

src - A ByteBuffer into which the data will be read.

pos - The offset from which the data will be read.

Returns:

The #of disk read operations that were required.

Throws:

IOException

IllegalArgumentException - if any parameter is null.

IllegalArgumentException - if pos is negative.

IllegalArgumentException - if dst does not have any bytes remaining.

readAll

public static int readAll(IReopenChannel<FileChannel> opener,
          ByteBuffer src,
          long pos)
                   throws IOException

Reads Buffer.remaining() bytes into the caller's ByteBuffer from the channel starting at offset pos. The position of the ByteBuffer is advanced to the limit. The offset of the channel is NOT modified as a side-effect.

This handles partial reads by reading until nbytes bytes have been transferred.

Parameters:

opener - An object which knows how to re-open the FileChannel and knows when the resource is no longer available.

src - A ByteBuffer into which the data will be read.

pos - The offset from which the data will be read.

Returns:

The #of disk read operations that were required.

Throws:

IOException

IllegalArgumentException - if any parameter is null.

IllegalArgumentException - if pos is negative.

IllegalArgumentException - if dst does not have any bytes remaining.

readAllAsync

public static long readAllAsync(FileChannelUtility.IAsyncOpener opener,
                List<FileChannelUtility.AsyncTransfer> transfers)
                         throws IOException

readAllAsync will make repeated attempts to read data into the transfer buffers defined in the List of AsyncTransfer instances.

Parameters:

opener - provides AsynchronouseFileChannel

transfers - defines the list of required transfers

Returns:

the total number of bytes read asynchronously

Throws:

IOException

writeAll

public static int writeAll(FileChannel channel,
           ByteBuffer data,
           long pos)
                    throws IOException

Deprecated. by writeAll(IReopenChannel, ByteBuffer, long)

Write bytes in data from the position to the limit on the channel starting at pos. The position of the buffer will be advanced to the limit. The position of the channel is not changed by this method.

Note: I have seen count != remaining() for a single invocation of FileChannel#write(). This occurred 5 hours into a run with the write cache disabled (so lots of small record writes). All of a sudden, several writes wound up reporting too few bytes written - this persisted until the end of the run (Fedora core 6 with Sun JDK 1.6.0_03). I have since modified this code to use a loop to ensure that all bytes get written.

Returns:

The #of disk write operations that were required.

Throws:

IOException

writeAll

public static int writeAll(IReopenChannel<FileChannel> opener,
           ByteBuffer data,
           long pos)
                    throws IOException

Write bytes in data from the position to the limit on the channel starting at pos. The position of the buffer will be advanced to the limit. The position of the channel is not changed by this method. If the backing channel is asynchronously in another thread closed then it will be re-opened and the write will continue.

Note: I have seen count != remaining() for a single invocation of FileChannel#write(). This occurred 5 hours into a run with the write cache disabled (so lots of small record writes). All of a sudden, several writes wound up reporting too few bytes written - this persisted until the end of the run (Fedora core 6 with Sun JDK 1.6.0_03). I have since modified this code to use a loop to ensure that all bytes get written.

Parameters:

opener -

data -

pos -

Returns:

The #of disk write operations that were required.

Throws:

IOException

transferAll

public static int transferAll(FileChannel sourceChannel,
              long fromPosition,
              long count,
              RandomAccessFile out,
              long toPosition)
                       throws IOException

FileChannel to FileChannel transfer of count bytes from the sourceChannel starting at the fromPosition onto the out file starting at its current position. The position on the sourceChannel is updated by this method and will be the positioned after the last byte transferred (this is done by FileChannel.transferFrom(java.nio.channels.ReadableByteChannel, long, long) so we have no choice about that). The position on the out file is updated by this method and will be located after the last byte transferred (this is done since we may have to extend the output file in which case its position will have been changed anyway so this makes the API more uniform).

Parameters:

sourceChannel - The source FileChannel.

fromPosition - The first byte to transfer from the sourceChannel.

count - The #of bytes to transfer.

out - The output file.

toPosition - The data will be transferred onto the output channel starting at this position.

Returns:

#of IO operations required to effect the transfer.

Throws:

IOException