org.mmtk.policy

Class LargeObjectSpace

java.lang.Object

org.mmtk.policy.Space

org.mmtk.policy.BaseLargeObjectSpace

org.mmtk.policy.LargeObjectSpace

public final class LargeObjectSpace
extends BaseLargeObjectSpace

Each instance of this class corresponds to one explicitly managed large object 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
static int	GLOBAL_GC_BITS_REQUIRED
private boolean	inNurseryGC
static int	LOCAL_GC_BITS_REQUIRED
private static byte	LOS_BIT_MASK
private static byte	MARK_BIT
private byte	markState
private static byte	NURSERY_BIT
private Treadmill	treadmill

Fields inherited from class org.mmtk.policy.BaseLargeObjectSpace

PAGE_MASK

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
LargeObjectSpace(String name, boolean zeroed, VMRequest vmRequest) The caller specifies the region of virtual memory to be used for this space.
LargeObjectSpace(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
protected int	cellHeaderSize() Return the size of the per-cell header for cells of a given class size.
Treadmill	getTreadmill() This is the treadmill used by the large object space.
void	initializeHeader(ObjectReference object, boolean alloc) Perform any required initialization of the GC portion of the header.
private void	internalMarkObject(ObjectReference object, boolean nurseryObject) An object has been marked (identifiged as live).
private boolean	isInNursery(ObjectReference object) Return true if the object is in the logical nursery
boolean	isLive(ObjectReference object) Is the object in this space alive?
void	prepare(boolean fullHeap) Prepares for a new collection increment.
void	release(Address first) Release a unit of allocation (a page or pages)
void	release(boolean fullHeap) A new collection increment has completed.
protected int	superPageHeaderSize() Return the size of the per-superpage header required by this system.
private void	sweepLargePages(boolean sweepNursery) Sweeps through the large pages, releasing all superpages on the "from space" treadmill.
private boolean	testAndMark(ObjectReference object, byte value) Atomically attempt to set the mark bit of an object.
private boolean	testMarkBit(ObjectReference object, byte value) Return true if the mark bit for an object has the given value.
ObjectReference	traceObject(TransitiveClosure trace, ObjectReference object) Trace a reference to an object under a mark sweep collection policy.

Methods inherited from class org.mmtk.policy.BaseLargeObjectSpace

free, getHeaderSize, getSize, getSuperPage

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, isReachable, 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

MARK_BIT

private static final byte MARK_BIT

See Also:

Constant Field Values

NURSERY_BIT

private static final byte NURSERY_BIT

See Also:

Constant Field Values

LOS_BIT_MASK

private static final byte LOS_BIT_MASK

See Also:

Constant Field Values

markState

private byte markState

inNurseryGC

private boolean inNurseryGC

treadmill

private final Treadmill treadmill

Constructor Detail

LargeObjectSpace

public LargeObjectSpace(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.

LargeObjectSpace

public LargeObjectSpace(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

prepare

public void prepare(boolean fullHeap)

Prepares for a new collection increment. For the mark-sweep collector we must flip the state of the mark bit between collections.

Parameters:

fullHeap - whether the collection will be full heap

release

public void release(boolean fullHeap)

A new collection increment has completed. For the mark-sweep collector this means we can perform the sweep phase.

Parameters:

fullHeap - whether the collection was full heap

sweepLargePages

private void sweepLargePages(boolean sweepNursery)

Sweeps through the large pages, releasing all superpages on the "from space" treadmill.

Parameters:

sweepNursery - whether to sweep the nursery

release

public void release(Address first)

Description copied from class: Space

Release a unit of allocation (a page or pages)

Specified by:

release in class Space

Parameters:

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

traceObject

public ObjectReference traceObject(TransitiveClosure trace,
                                   ObjectReference object)

Trace a reference to an object under a mark sweep collection policy. If the object header is not already marked, mark the object in either the bitmap or by moving it off the treadmill, and 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 (there is no object forwarding in this collector, so we always return the same object: this could be a void method but for compliance to a more general interface).

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 in question

Returns:

true if this object is known to be live (i.e. it is marked)

internalMarkObject

private void internalMarkObject(ObjectReference object,
                                boolean nurseryObject)

An object has been marked (identifiged as live). Large objects are added to the to-space treadmill, while all other objects will have a mark bit set in the superpage header.

Parameters:

object - The object which has been marked.

nurseryObject - whether the object is in the nursery

initializeHeader

public void initializeHeader(ObjectReference object,
                             boolean alloc)

Perform any required initialization of the GC portion of the header.

Parameters:

object - the object ref to the storage to be initialized

alloc - is this initialization occurring due to (initial) allocation (true) or due to copying (false)?

testAndMark

private boolean testAndMark(ObjectReference object,
                            byte value)

Atomically attempt to set the mark bit of an object.

Parameters:

object - The object whose mark bit is to be written

value - The value to which the mark bit will be set

Returns:

true if successful, false if the mark bit was already set.

testMarkBit

private boolean testMarkBit(ObjectReference object,
                            byte value)

Return true if the mark bit for an object has the given value.

Parameters:

object - The object whose mark bit is to be tested

value - The value against which the mark bit will be tested

Returns:

true if the mark bit for the object has the given value.

isInNursery

private boolean isInNursery(ObjectReference object)

Return true if the object is in the logical nursery

Parameters:

object - The object whose status is to be tested

Returns:

true if the object is in the logical nursery

superPageHeaderSize

protected int superPageHeaderSize()

Description copied from class: BaseLargeObjectSpace

Return the size of the per-superpage header required by this system. In this case it is just the underlying superpage header size.

Specified by:

superPageHeaderSize in class BaseLargeObjectSpace

Returns:

The size of the per-superpage header required by this system.

cellHeaderSize

protected int cellHeaderSize()

Description copied from class: BaseLargeObjectSpace

Return the size of the per-cell header for cells of a given class size.

Specified by:

cellHeaderSize in class BaseLargeObjectSpace

Returns:

The size of the per-cell header for cells of a given class size.

getTreadmill

public Treadmill getTreadmill()

This is the treadmill used by the large object space. Note that it depends on the specific local in use whether this is being used.

Returns:

The treadmill associated with this large object space.