uk.ac.starlink.fits

Class BufferManager

java.lang.Object

uk.ac.starlink.fits.BufferManager

public class BufferManager
extends Object

Manages access to a region of a file using monolithic byte buffers. The region is only mapped once, and subsequent buffer requests are handled by duplicating the original mapped buffer.

Buffers are acquired using createBuffer(), and should be disposed of using disposeBuffer(java.nio.ByteBuffer) when no longer in use. When none of the buffers are in use any more, close() should be called.

Note: the mapped buffer is unmapped using the supplied Unmapper when all created buffers have been disposed, or when close() is called. If any of the created buffers is used after this has happened, and unmapping is actually attempted, very bad consequences may ensue. Therefore this class, or at least its disposeBuffer(java.nio.ByteBuffer) and close() methods, should be used with extreme caution, or a null Unmapper should be supplied.

Since:

12 May 2022

Author:

Mark Taylor

Constructor Summary

Constructors

Constructor and Description
BufferManager(FileChannel channel, long offset, int leng, String logLabel, Unmapper unmapper) Constructor.

Method Summary

Modifier and Type	Method and Description
void	close() Asserts that neither this manager, nor any of the buffers it has supplied, will be used again.
ByteBuffer	createBuffer() Returns a new read-only ByteBuffer providing access to the file region.
void	disposeBuffer(ByteBuffer buf) Asserts that the supplied buffer, originally acquired from createBuffer(), will no longer be used.

Methods inherited from class java.lang.Object

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

Constructor Detail

BufferManager

public BufferManager(FileChannel channel,
                     long offset,
                     int leng,
                     String logLabel,
                     Unmapper unmapper)

Constructor.

Parameters:

channel - file channel

offset - offset into file of start of mapped region

leng - length of mapped region

logLabel - description of mapped region suitable for use in logging messages

unmapper - used to unmap buffers, may be null for safety

Method Detail

createBuffer

public ByteBuffer createBuffer()
                        throws IOException

Returns a new read-only ByteBuffer providing access to the file region. The returned object should if possible be passed to disposeBuffer(java.nio.ByteBuffer) after it is known that it will no longer be used.

Returns:

buffer

Throws:

IOException

disposeBuffer

public void disposeBuffer(ByteBuffer buf)

Asserts that the supplied buffer, originally acquired from createBuffer(), will no longer be used. Resources may be reclaimed.

Parameters:

buf - previously created buffer

close

public void close()

Asserts that neither this manager, nor any of the buffers it has supplied, will be used again.