org.mmtk.policy

Class ImmortalSpace

java.lang.Object

org.mmtk.policy.Space

org.mmtk.policy.ImmortalSpace

public final class ImmortalSpace
extends Space

This class implements tracing for a simple immortal collection policy. Under this policy all that is required is for the "collector" to propagate marks in a liveness trace. It does not actually collect. This class does not hold any state, all methods are static.

Nested Class Summary

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

Space.SpaceVisitor

Field Summary

Fields

Modifier and Type	Field and Description
(package private) static byte	GC_MARK_BIT_MASK
private byte	markState
private static int	META_DATA_PAGES_PER_REGION

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
ImmortalSpace(String name, boolean zeroed, VMRequest vmRequest) The caller specifies the region of virtual memory to be used for this space.
ImmortalSpace(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
Word	getMarkState()
void	initializeHeader(ObjectReference object) Initialize the object header post-allocation.
boolean	isLive(ObjectReference object) Is the object in this space alive?
boolean	isReachable(ObjectReference object) Returns if the object in question is currently thought to be reachable.
void	prepare() Prepare for a new collection increment.
void	release()
void	release(Address start) Release an allocated page or pages.
private static boolean	testAndMark(ObjectReference object, byte value) Used to mark boot image objects during a parallel scan of objects during GC.
ObjectReference	traceObject(TransitiveClosure trace, ObjectReference object) Trace a reference to an object under an immortal 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

GC_MARK_BIT_MASK

static final byte GC_MARK_BIT_MASK

See Also:

Constant Field Values

META_DATA_PAGES_PER_REGION

private static final int META_DATA_PAGES_PER_REGION

markState

private byte markState

Constructor Detail

ImmortalSpace

public ImmortalSpace(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.

ImmortalSpace

public ImmortalSpace(String name,
                     boolean zeroed,
                     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)

zeroed - if true, allocations return zeroed memory.

vmRequest - An object describing the virtual memory requested.

Method Detail

getMarkState

public Word getMarkState()

Returns:

the current mark state

initializeHeader

public void initializeHeader(ObjectReference object)

Initialize the object header post-allocation. We need to set the mark state correctly and set the logged bit if necessary.

Parameters:

object - The newly allocated object instance whose header we are initializing

testAndMark

private static boolean testAndMark(ObjectReference object,
                                   byte value)

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

Parameters:

object - the object to mark

value - the mark value

Returns:

true if marking was done.

traceObject

public ObjectReference traceObject(TransitiveClosure trace,
                                   ObjectReference object)

Trace a reference to an object under an immortal collection policy. If the object is not already marked, enqueue the object for subsequent processing. The object is marked as (an atomic) side-effect of checking whether already marked.

Specified by:

traceObject in class Space

Parameters:

trace - The trace being conducted.

object - The object to be traced.

Returns:

The object, forwarded, if appropriate

prepare

public void prepare()

Prepare for a new collection increment. For the immortal collector we must flip the state of the mark bit between collections.

release

public void release()

release

public void release(Address start)

Release an allocated page or pages. In this case we do nothing because we only release pages enmasse.

Specified by:

release in class Space

Parameters:

start - The address of the start of the page or pages

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)

Returns if the object in question is currently thought to be reachable. This is done by comparing the mark bit to the current mark state. For the immortal collector reachable and live are different, making this method necessary.

Overrides:

isReachable in class Space

Parameters:

object - The address of an object in immortal space to test

Returns:

true if ref may be a reachable object (e.g., having the current mark state). While all immortal objects are live, some may be unreachable.