org.jlab.coda.jevio

Class MappedMemoryHandler

java.lang.Object

org.jlab.coda.jevio.MappedMemoryHandler

public class MappedMemoryHandler
extends java.lang.Object

This is a class designed to handle access of evio version 4 format files with size greater than 2.1 GBytes. Currently the largest size memory map that Java can handle is Integer.MAX_VALUE which limits the use of memory mapping to looking at files that size or smaller. This class circumvents this limit by viewing large files as a collection of multiple memory maps.

The problem is that we do NOT want an evio event which is split between 2 different memory maps. This is addressed by scanning a memory map of the largest size to find the last complete evio block it contains. The next memory map then starts at the following block.

Just a note about synchronization. This object is NOT threadsafe but it doesn't have to be since its use in EvioReader is synchronized and therefore there should be not be thread unsafe.

Author:

timmer

Constructor Summary

Constructors

Constructor and Description
MappedMemoryHandler(java.nio.ByteBuffer evioBuf) Constructor.
MappedMemoryHandler(java.nio.channels.FileChannel channel, java.nio.ByteOrder byteOrder) Constructor.

Method Summary

Modifier and Type	Method and Description
int	getBlockCount() Get the number of evio blocks in the file/buffer.
java.nio.ByteBuffer	getByteBuffer(int eventNumber) Get the ByteBuffer object containing the event of interest.
int	getEventCount() Get the number of evio events in the file/buffer.
java.nio.ByteBuffer	getFirstMap() Get the first memory map - used to map the beginning of the file.
int	getMapCount() Get the number of memory maps used to fully map file.
boolean	isEvioErrorCondition() Is there an evio error in the file/buffer.

Methods inherited from class java.lang.Object

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

Constructor Detail

MappedMemoryHandler

public MappedMemoryHandler(java.nio.channels.FileChannel channel,
                           java.nio.ByteOrder byteOrder)
                    throws java.io.IOException

Constructor. File format errors are flagged, but no exception is thrown.

Parameters:

channel - file's file channel object

byteOrder - byte order of the data

Throws:

java.io.IOException - if could not map file

MappedMemoryHandler

public MappedMemoryHandler(java.nio.ByteBuffer evioBuf)

Constructor.

Parameters:

evioBuf - buffer to analyze

Method Detail

isEvioErrorCondition

public boolean isEvioErrorCondition()

Is there an evio error in the file/buffer.

Returns:

true if error, else false

getEventCount

public int getEventCount()

Get the number of evio events in the file/buffer.

Returns:

number of evio events in the file/buffer.

getBlockCount

public int getBlockCount()

Get the number of evio blocks in the file/buffer.

Returns:

number of evio blocks in the file/buffer.

getMapCount

public int getMapCount()

Get the number of memory maps used to fully map file.

Returns:

number of memory maps used to fully map file.

getFirstMap

public java.nio.ByteBuffer getFirstMap()

Get the first memory map - used to map the beginning of the file.

Returns:

first memory map - used to map the beginning of the file.

getByteBuffer

public java.nio.ByteBuffer getByteBuffer(int eventNumber)

Get the ByteBuffer object containing the event of interest. Position in the buffer is properly set to start reading.

Parameters:

eventNumber - number of the desired event (starting at 0)

Returns:

the ByteBuffer object containing the event of interest.