org.mmtk.policy

Class MarkCompactSpace

java.lang.Object

org.mmtk.policy.Space

org.mmtk.policy.MarkCompactSpace

public final class MarkCompactSpace
extends Space

This class implements functionality for a simple sliding mark-compact space.

Nested Class Summary

Nested classes/interfaces inherited from class org.mmtk.policy.Space

Space.SpaceVisitor

Field Summary

Fields

Modifier and Type	Field and Description
private static Offset	FORWARDING_POINTER_OFFSET
static int	GC_HEADER_WORDS_REQUIRED
private static Word	GC_MARK_BIT_MASK
static int	GLOBAL_GC_BITS_REQUIRED
static int	LOCAL_GC_BITS_REQUIRED
private static Lock	lock
private Address	regionList The list of occupied regions

Fields inherited from class org.mmtk.policy.Space

AVAILABLE_BYTES, AVAILABLE_END, AVAILABLE_PAGES, AVAILABLE_START, BYTES_IN_CHUNK, contiguous, descriptor, extent, headDiscontiguousRegion, HEAP_END, HEAP_START, immortal, LOG_ADDRESS_SPACE, LOG_BYTES_IN_CHUNK, MAX_CHUNKS, MAX_SPACES, movable, PAGES_IN_CHUNK, pr, start, zeroed

Constructor Summary

Constructors

Constructor and Description
MarkCompactSpace(String name, VMRequest vmRequest) The caller specifies the region of virtual memory to be used for this space.

Method Summary

Modifier and Type	Method and Description
void	append(Address region) Append a region or list of regions to the global list
static void	appendRegion(Address listHead, Address region)
static void	clearForwardingPointer(ObjectReference object) Non-atomic clear of forwarding pointer word (assumption, thread doing the set has done attempt to forward and owns the right to copy the object)
static void	clearMark(ObjectReference object)
static ObjectReference	getForwardingPointer(ObjectReference object) Non-atomic read of forwarding pointer
Address	getNextRegion()
void	initializeHeader(ObjectReference object) Initialise the header of the object.
boolean	isLive(ObjectReference object) Is the object in this space alive?
static boolean	isMarked(ObjectReference object)
boolean	isReachable(ObjectReference object) Has the object in this space been reached during the current collection.
void	postAlloc(ObjectReference object) Perform any required post-allocation initialization Nothing to be done in this case
void	prepare() Prepare for a collection
void	release() Release after a collection
void	release(Address start) Release a unit of allocation (a page or pages)
static void	setForwardingPointer(ObjectReference object, ObjectReference ptr) Non-atomic write of forwarding pointer word (assumption, thread doing the set has done attempt to forward and owns the right to copy the object)
private static boolean	testAndClearMark(ObjectReference object) Used to mark boot image objects during a parallel scan of objects during GC Returns true if marking was done.
static boolean	testAndMark(ObjectReference object) Used to mark boot image objects during a parallel scan of objects during GC.
static boolean	toBeCompacted(ObjectReference object)
ObjectReference	traceForwardObject(TraceLocal trace, ObjectReference object) Trace an object under a copying collection policy.
ObjectReference	traceMarkObject(TraceLocal trace, ObjectReference object) Trace an object under a copying collection policy.
ObjectReference	traceObject(TransitiveClosure trace, ObjectReference object) Trace an object under a copying collection policy.

Methods inherited from class org.mmtk.policy.Space

acquire, availablePhysicalPages, chunkAlign, chunkAlign, committedPages, cumulativeCommittedPages, eagerlyMmapMMTkContiguousSpaces, eagerlyMmapMMTkDiscontiguousSpaces, eagerlyMmapMMTkSpaces, getDescriptor, getDiscontigEnd, getDiscontigStart, getExtent, getFracAvailable, getHeadDiscontiguousRegion, getIndex, getName, getSpaceCount, getSpaceForAddress, getSpaceForObject, getSpaces, getStart, growDiscontiguousSpace, growSpace, isImmortal, isImmortal, isInSpace, isInSpace, isMappedAddress, isMappedObject, isMovable, isMovable, printUsageMB, printUsagePages, printVMMap, releaseAllChunks, releaseDiscontiguousChunks, requiredChunks, reservedPages, setZeroingApproach, skipConcurrentZeroing, triggerConcurrentZeroing, visitSpaces

Methods inherited from class java.lang.Object

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

Field Detail

LOCAL_GC_BITS_REQUIRED

public static final int LOCAL_GC_BITS_REQUIRED

See Also:

Constant Field Values

GLOBAL_GC_BITS_REQUIRED

public static final int GLOBAL_GC_BITS_REQUIRED

See Also:

Constant Field Values

GC_HEADER_WORDS_REQUIRED

public static final int GC_HEADER_WORDS_REQUIRED

See Also:

Constant Field Values

GC_MARK_BIT_MASK

private static final Word GC_MARK_BIT_MASK

FORWARDING_POINTER_OFFSET

private static final Offset FORWARDING_POINTER_OFFSET

lock

private static final Lock lock

regionList

private Address regionList

The list of occupied regions

Constructor Detail

MarkCompactSpace

public MarkCompactSpace(String name,
                        VMRequest vmRequest)

The caller specifies the region of virtual memory to be used for this space. If this region conflicts with an existing space, then the constructor will fail.

Parameters:

name - The name of this space (used when printing error messages etc)

vmRequest - An object describing the virtual memory requested.

Method Detail

prepare

public void prepare()

Prepare for a collection

release

public void release()

Release after a collection

release

public void release(Address start)

Release a unit of allocation (a page or pages)

In this case we do nothing ecause we only release pages enmasse.

Specified by:

release in class Space

Parameters:

start - The address of the start of the region to be released

traceObject

public ObjectReference traceObject(TransitiveClosure trace,
                                   ObjectReference object)

Trace an object under a copying collection policy. If the object is already copied, the copy is returned. Otherwise, a copy is created and returned. In either case, the object will be marked on return.

Specified by:

traceObject in class Space

Parameters:

trace - The trace being conducted.

object - The object to be forwarded.

Returns:

The forwarded object.

traceMarkObject

public ObjectReference traceMarkObject(TraceLocal trace,
                                       ObjectReference object)

Trace an object under a copying collection policy. If the object is already copied, the copy is returned. Otherwise, a copy is created and returned. In either case, the object will be marked on return.

Parameters:

trace - The trace being conducted.

object - The object to be forwarded.

Returns:

The forwarded object.

traceForwardObject

public ObjectReference traceForwardObject(TraceLocal trace,
                                          ObjectReference object)

Trace an object under a copying collection policy. If the object is already copied, the copy is returned. Otherwise, a copy is created and returned. In either case, the object will be marked on return.

Parameters:

trace - The trace being conducted.

object - The object to be forwarded.

Returns:

The forwarded object.

isLive

public boolean isLive(ObjectReference object)

Description copied from class: Space

Is the object in this space alive?

Specified by:

isLive in class Space

Parameters:

object - The object reference.

Returns:

true if the object is live.

isReachable

public boolean isReachable(ObjectReference object)

Description copied from class: Space

Has the object in this space been reached during the current collection. This is used for GC Tracing.

Overrides:

isReachable in class Space

Parameters:

object - The object reference.

Returns:

true if the object is reachable.

postAlloc

public void postAlloc(ObjectReference object)

Perform any required post-allocation initialization Nothing to be done in this case

Parameters:

object - the object ref to the storage to be initialized

getForwardingPointer

public static ObjectReference getForwardingPointer(ObjectReference object)

Non-atomic read of forwarding pointer

Parameters:

object - The object whose forwarding pointer is to be read

Returns:

The forwarding pointer stored in object's header.

initializeHeader

public void initializeHeader(ObjectReference object)

Initialise the header of the object.

Parameters:

object - The object to initialise

testAndMark

public static boolean testAndMark(ObjectReference object)

Used to mark boot image objects during a parallel scan of objects during GC.

Parameters:

object - The object to be marked

Returns:

true if marking was done.

isMarked

public static boolean isMarked(ObjectReference object)

Parameters:

object - the object in question

Returns:

true if the object is marked

testAndClearMark

private static boolean testAndClearMark(ObjectReference object)

Used to mark boot image objects during a parallel scan of objects during GC Returns true if marking was done.

Parameters:

object - The object to be marked

Returns:

true if marking was done, false otherwise

toBeCompacted

public static boolean toBeCompacted(ObjectReference object)

clearMark

public static void clearMark(ObjectReference object)

setForwardingPointer

public static void setForwardingPointer(ObjectReference object,
                                        ObjectReference ptr)

Non-atomic write of forwarding pointer word (assumption, thread doing the set has done attempt to forward and owns the right to copy the object)

Parameters:

object - The object whose forwarding pointer is to be set

ptr - The forwarding pointer to be stored in the object's forwarding word

clearForwardingPointer

public static void clearForwardingPointer(ObjectReference object)

Non-atomic clear of forwarding pointer word (assumption, thread doing the set has done attempt to forward and owns the right to copy the object)

Parameters:

object - The object whose forwarding pointer is to be set

getNextRegion

public Address getNextRegion()

Returns:

A region of this space that has net yet been compacted during the current collection

append

public void append(Address region)

Append a region or list of regions to the global list

Parameters:

region - the region to append

appendRegion

public static void appendRegion(Address listHead,
                                Address region)