org.mmtk.policy

Class ExplicitFreeListSpace

java.lang.Object

org.mmtk.policy.Space

org.mmtk.policy.SegregatedFreeListSpace

org.mmtk.policy.ExplicitFreeListSpace

public final class ExplicitFreeListSpace
extends SegregatedFreeListSpace

Each instance of this class corresponds to one *space*. Each of the instance methods of this class may be called by any thread (i.e. synchronization must be explicit in any instance or class method). This contrasts with the MarkSweepLocal, where instances correspond to *plan* instances and therefore to kernel threads. Thus unlike this class, synchronization is not necessary in the instance methods of MarkSweepLocal.

Nested Class Summary

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

SegregatedFreeListSpace.Sweeper

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

Space.SpaceVisitor

Field Summary

Fields

Modifier and Type	Field and Description
static int	GC_HEADER_WORDS_REQUIRED
static int	GLOBAL_GC_BITS_REQUIRED
static int	LOCAL_GC_BITS_REQUIRED

Fields inherited from class org.mmtk.policy.SegregatedFreeListSpace

availableBlockHead, consumedBlockHead, flushedBlockHead, LAZY_SWEEP, lock, MAX_CELL_SIZE, MAX_CELLS, MAX_FREELIST_OBJECT_BYTES, META_DATA_PAGES_PER_REGION_NO_BITMAP, META_DATA_PAGES_PER_REGION_WITH_BITMAP, MIN_CELLS, WORST_CASE_FRAGMENTATION

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
ExplicitFreeListSpace(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 Address	advanceToBlock(Address block, int sizeClass) Prepare the next block in the free block list for use by the free list allocator.
void	free(ObjectReference object) Free an object.
boolean	isLive(ObjectReference object) Is the object in this space alive?
protected boolean	maintainSideBitmap()
protected void	notifyNewBlock(Address block, int sizeClass) Notify that a new block has been installed.
void	prepare() Prepare for a new collection increment.
protected boolean	preserveFreeList()
void	release() A new collection increment has completed.
void	release(Address start) Release an allocated page or pages
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.SegregatedFreeListSpace

clearAllBlockMarks, clearBlockMark, clearLiveBit, clearLiveBit, clearLiveBits, consumeBlocks, containsLiveCell, flushAvailableBlocks, getAllocationBlock, getBaseCellSize, getFreeList, getSizeClass, isCellLive, liveBitSet, liveBitSet, makeFreeList, markBlock, markBlock, parallelSweepCells, reclaimCellForObject, returnBlock, returnConsumedBlock, setFreeList, sizeClassCount, sweepBlock, sweepCells, sweepCells, sweepConsumedBlocks, testAndSetLiveBit, unsyncClearLiveBit, unsyncClearLiveBit, unsyncSetLiveBit, zeroLiveBits

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

GC_HEADER_WORDS_REQUIRED

public static final int GC_HEADER_WORDS_REQUIRED

See Also:

Constant Field Values

Constructor Detail

ExplicitFreeListSpace

public ExplicitFreeListSpace(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

maintainSideBitmap

protected boolean maintainSideBitmap()

Specified by:

maintainSideBitmap in class SegregatedFreeListSpace

Returns:

whether SegregatedFreeListSpace should manage a side bitmap to keep track of live objects

preserveFreeList

protected boolean preserveFreeList()

Specified by:

preserveFreeList in class SegregatedFreeListSpace

Returns:

whether free lists need to be preserved when blocks are moved around

advanceToBlock

protected Address advanceToBlock(Address block,
                                 int sizeClass)

Prepare the next block in the free block list for use by the free list allocator. In the case of lazy sweeping this involves sweeping the available cells. The sweeping operation must ensure that cells are pre-zeroed, as this method must return pre-zeroed cells.

Specified by:

advanceToBlock in class SegregatedFreeListSpace

Parameters:

block - The block to be prepared for use

sizeClass - The size class of the block

Returns:

The address of the first pre-zeroed cell in the free list for this block, or zero if there are no available cells.

notifyNewBlock

protected void notifyNewBlock(Address block,
                              int sizeClass)

Description copied from class: SegregatedFreeListSpace

Notify that a new block has been installed. This is to ensure that appropriate collection state can be initialized for the block

Overrides:

notifyNewBlock in class SegregatedFreeListSpace

Parameters:

block - The new block

sizeClass - The block's sizeclass.

free

public void free(ObjectReference object)

Free an object.

Parameters:

object - The object to be freed.

prepare

public void prepare()

Prepare for a new collection increment.

release

public void release()

A new collection increment has completed.

release

public void release(Address start)

Release an allocated page or pages

Specified by:

release in class Space

Parameters:

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

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:

object - The object to be traced.

trace - The trace being conducted.

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 reference.

Returns:

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