org.jikesrvm.objectmodel

Class FieldLayoutContext

java.lang.Object

org.jikesrvm.objectmodel.FieldLayoutContext

Direct Known Subclasses:

FieldLayoutPacked.LayoutContext, FieldLayoutUnpacked.LayoutContext

public abstract class FieldLayoutContext
extends Object

State for the field layout engine. Subtypes of this are closely tied to field layout schemes, and are generally defined in same.

A FieldLayoutContext deals in an abstract offset space, where there is no header, and fields are laid out relative to 0.

This abstract superclass looks after the total object size and alignment.

Field Summary

Fields

Modifier and Type	Field and Description
private byte	alignment Alignment requirements.
protected static int	OBJECT_SIZE_ALIGN
private int	objectSize The size of the current object as laid out

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	FieldLayoutContext(byte alignment)
protected	FieldLayoutContext(byte alignment, FieldLayoutContext superLayout) Constructor for an object with a superclass.

Method Summary

Modifier and Type	Method and Description
protected void	adjustAlignment(int fieldSize) Adjust alignment to the next highest value.
protected void	ensureObjectSize(int size) Adjust the size of the object if necessary to accommodate a field.
(package private) int	getAlignment()
protected int	getObjectSize()
(package private) abstract int	nextOffset(int size, boolean isReference)
protected void	setObjectSize(int size) Set the current size of the object (excluding header)

Methods inherited from class java.lang.Object

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

Field Detail

OBJECT_SIZE_ALIGN

protected static final int OBJECT_SIZE_ALIGN

See Also:

Constant Field Values

alignment

private byte alignment

Alignment requirements.

objectSize

private int objectSize

The size of the current object as laid out

Constructor Detail

FieldLayoutContext

protected FieldLayoutContext(byte alignment)

Parameters:

alignment - the alignment to use for this context

FieldLayoutContext

protected FieldLayoutContext(byte alignment,
                             FieldLayoutContext superLayout)

Constructor for an object with a superclass. The superclass is used to initialize the layout.

Parameters:

alignment - the alignment to use for this context

superLayout - the super class' layout

Method Detail

nextOffset

abstract int nextOffset(int size,
                        boolean isReference)

Parameters:

size - the field's size in bytes

isReference - whether the field is a reference field

Returns:

the offset of a new field of the given size

adjustAlignment

protected void adjustAlignment(int fieldSize)

Adjust alignment to the next highest value. In Java, the only 2 possibilities are int-aligned or long-aligned.

Parameters:

fieldSize - the size of the field in bytes

getAlignment

int getAlignment()

Returns:

the current alignment value

getObjectSize

protected int getObjectSize()

Returns:

The current size of the object (excluding header)

setObjectSize

protected void setObjectSize(int size)

Set the current size of the object (excluding header)

Parameters:

size - the object's size, excluding the header

ensureObjectSize

protected void ensureObjectSize(int size)

Adjust the size of the object if necessary to accommodate a field.

Parameters:

size - The size occupied by data fields in the object.