HeaderByte (Jikes RVM API)

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org.mmtk.utility
Class HeaderByte

java.lang.Object
  org.mmtk.utility.HeaderByte

public class HeaderByte
extends Object
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
`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
`HeaderByte()`

Method Summary
`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)`
`static byte`	`setBuildTimeGCByte(Address object, ObjectReference typeRef, int size)` Perform any required initialization of the GC portion of the header.

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

setBuildTimeGCByte

public static byte setBuildTimeGCByte(Address object,
                                      ObjectReference typeRef,
                                      int size)

Perform any required initialization of the GC portion of the header. Called for objects created at boot time.

Parameters:: object - the Address representing the storage to be initialized; typeRef - the type reference for the instance being created; size - the number of bytes allocated by the GC system for this object.
Returns:: The new value of the status word

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).