org.mmtk.utility

Class HeaderByte

java.lang.Object

org.mmtk.utility.HeaderByte

public class HeaderByte
extends Object

This class provides generic support for operations over the GC byte within each object's header word. Specifically this class manages global status bits which cut across policies (for example the logging bit).

The general pattern for use of the GC byte is that the high order bits successively reserved for global use, as necessary. Any GC policy may use those bits that are not reserved for global use.

Field Summary

Fields

Modifier and Type	Field and Description
static boolean	NEEDS_UNLOGGED_BIT
private static int	TOTAL_BITS
static byte	UNLOGGED_BIT
private static int	UNLOGGED_BIT_NUMBER
static int	USED_GLOBAL_BITS

Constructor Summary

Constructors

Constructor and Description
HeaderByte()

Method Summary

Modifier and Type	Method and Description
static boolean	isUnlogged(ObjectReference object) Return true if the specified object needs to be logged.
static void	markAsLogged(ObjectReference object) Mark an object as logged.
static void	markAsUnlogged(ObjectReference object)

Methods inherited from class java.lang.Object

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

Field Detail

TOTAL_BITS

private static final int TOTAL_BITS

See Also:

Constant Field Values

NEEDS_UNLOGGED_BIT

public static final boolean NEEDS_UNLOGGED_BIT

UNLOGGED_BIT_NUMBER

private static final int UNLOGGED_BIT_NUMBER

UNLOGGED_BIT

public static final byte UNLOGGED_BIT

USED_GLOBAL_BITS

public static final int USED_GLOBAL_BITS

Constructor Detail

HeaderByte

public HeaderByte()

Method Detail

markAsUnlogged

public static void markAsUnlogged(ObjectReference object)

markAsLogged

public static void markAsLogged(ObjectReference object)

Mark an object as logged. Since duplicate logging does not raise any correctness issues, we do not worry about synchronization and allow threads to race to log the object, potentially including it twice (unlike reference counting where duplicates would lead to incorrect reference counts).

Parameters:

object - The object to be marked as logged

isUnlogged

public static boolean isUnlogged(ObjectReference object)

Return true if the specified object needs to be logged.

Parameters:

object - The object in question

Returns:

true if the object in question needs to be logged (remembered).