org.mmtk.plan.markcompact

Class MC

java.lang.Object

org.mmtk.plan.Plan

org.mmtk.plan.Simple

org.mmtk.plan.StopTheWorld

org.mmtk.plan.markcompact.MC

public class MC
extends StopTheWorld

This class implements the global state of a simple sliding mark-compact collector.

FIXME Need algorithmic overview and references.

All plans make a clear distinction between global and thread-local activities, and divides global and local state into separate class hierarchies. Global activities must be synchronized, whereas no synchronization is required for thread-local activities. There is a single instance of Plan (or the appropriate sub-class), and a 1:1 mapping of PlanLocal to "kernel threads" (aka CPUs). Thus instance methods of PlanLocal allow fast, unsychronized access to functions such as allocation and collection.

The global instance defines and manages static resources (such as memory and virtual memory resources). This mapping of threads to instances is crucial to understanding the correctness and performance properties of MMTk plans.

Field Summary

Fields

Modifier and Type	Field and Description
static short	CALCULATE_FP Calculate forwarding pointers via a linear scan over the heap
static short	COMPACT Perform compaction via a linear scan over the heap
static short	FORWARD_CLOSURE
Trace	forwardTrace This trace updates pointers with the forwarded references
static int	MARK_COMPACT The space descriptor
Trace	markTrace This trace sets the mark bit in live objects
short	mcCollection This is the phase that is executed to perform a mark-compact collection.
static MarkCompactSpace	mcSpace The mark compact space itself
static short	PREPARE_FORWARD
static short	RELEASE_FORWARD
static int	SCAN_FORWARD Specialized method identifier for the FORWARD phase
static int	SCAN_MARK Specialized method identifier for the MARK phase

Fields inherited from class org.mmtk.plan.StopTheWorld

postSanityPhase, preSanityPhase

Fields inherited from class org.mmtk.plan.Simple

CLOSURE, collection, collectionAttempt, COMPLETE, completeClosurePhase, FINALIZABLE, finishPhase, FORWARD, FORWARD_FINALIZABLE, FORWARD_REFS, forwardPhase, INITIATE, initPhase, PHANTOM_REFS, POST_SANITY_PLACEHOLDER, PRE_SANITY_PLACEHOLDER, PREPARE, PREPARE_STACKS, prepareStacks, refTypeClosurePhase, RELEASE, rootClosurePhase, ROOTS, SANITY_BUILD_TABLE, SANITY_CHECK_TABLE, SANITY_COPY_ROOTS, SANITY_PREPARE, SANITY_RELEASE, SANITY_ROOTS, SANITY_SET_POSTGC, SANITY_SET_PREGC, sanityBuildPhase, sanityCheckPhase, SET_COLLECTION_KIND, SOFT_REFS, STACK_ROOTS, WEAK_REFS, WEAK_TRACK_REFS

Fields inherited from class org.mmtk.plan.Plan

ALLOC_CODE, ALLOC_COLD_CODE, ALLOC_DEFAULT, ALLOC_GCSPY, ALLOC_HOT_CODE, ALLOC_IMMORTAL, ALLOC_LARGE_CODE, ALLOC_LOS, ALLOC_NON_MOVING, ALLOC_NON_REFERENCE, ALLOC_PRIMITIVE_LOS, ALLOC_STACK, allocationSiteCount, ALLOCATORS, concurrentWorkers, controlCollectorContext, DEFAULT_MAX_NURSERY, DEFAULT_MIN_NURSERY, DEFAULT_SITE, defaultCollectorContext, emergencyCollection, GATHER_WRITE_BARRIER_STATS, GC_PREPARE, GC_PROPER, IMMORTAL, immortalSpace, insideHarness, internalTriggeredCollection, LARGE_CODE, largeCodeSpace, lastInternalTriggeredCollection, LOS, loSpace, MAX_NON_LOS_COPY_BYTES, MAX_NON_LOS_DEFAULT_ALLOC_BYTES, MAX_NON_LOS_NONMOVING_ALLOC_BYTES, META, metaDataSpace, NEEDS_LOG_BIT_IN_HEADER, NON_MOVING, NON_PARTICIPANT, nonMovingSpace, NOT_IN_GC, parallelWorkers, pretenureThreshold, SANITY, sanityChecker, sanitySpace, SCAN_BOOT_IMAGE, SMALL_CODE, smallCodeSpace, stacksPrepared, totalTime, USE_CODE_SPACE, userTriggeredCollection, VM_SPACE, vmSpace

Constructor Summary

Constructors

Constructor and Description
MC() Constructor.

Method Summary

Modifier and Type	Method and Description
void	collectionPhase(short phaseId) Perform a (global) collection phase.
int	getPagesUsed() Return the number of pages reserved for use given the pending allocation.
protected void	registerSpecializedMethods() Registers specialized methods.
int	sanityExpectedRC(ObjectReference object, int sanityRootRC) Return the expected reference count.
boolean	willNeverMove(ObjectReference object) Can this object ever move.

Methods inherited from class org.mmtk.plan.StopTheWorld

processOptions

Methods inherited from class org.mmtk.plan.Simple

replacePhase, replacePlaceholderPhase, switchNurseryZeroingApproach

Methods inherited from class org.mmtk.plan.Plan

availableMemory, bootTimeWriteBarrier, collectionRequired, concurrentCollectionRequired, determineThreadCount, enableAllocation, enableCollection, forceFullHeapCollection, freeMemory, fullyBooted, gcInProgress, gcInProgressProper, getAllocationSite, getCollectionReserve, getPagesAvail, getPagesReserved, getSpecializedScanClass, getTotalPages, handleUserCollectionRequest, harnessBegin, harnessEnd, insertPhaseAfter, isCurrentGCNursery, isEmergencyCollection, isInitialized, isInternalTriggeredCollection, isUserTriggeredCollection, lastCollectionFullHeap, lastCollectionWasExhaustive, loadObjectReference, logPoll, notifyExit, poll, preCollectorSpawn, printDetailedTiming, printPostStats, printPreStats, printUsedPages, reservedMemory, resetCollectionTrigger, sanityLinearScan, setBuildTimeGCByte, setGCStatus, spawnCollectorThreads, stacksPrepared, startGCspyServer, storeObjectReference, stressTestGCRequired, totalMemory, triggerInternalCollectionRequest, usedMemory

Methods inherited from class java.lang.Object

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

Field Detail

mcSpace

public static final MarkCompactSpace mcSpace

The mark compact space itself

MARK_COMPACT

public static final int MARK_COMPACT

The space descriptor

SCAN_MARK

public static final int SCAN_MARK

Specialized method identifier for the MARK phase

See Also:

Constant Field Values

SCAN_FORWARD

public static final int SCAN_FORWARD

Specialized method identifier for the FORWARD phase

See Also:

Constant Field Values

PREPARE_FORWARD

public static final short PREPARE_FORWARD

FORWARD_CLOSURE

public static final short FORWARD_CLOSURE

RELEASE_FORWARD

public static final short RELEASE_FORWARD

CALCULATE_FP

public static final short CALCULATE_FP

Calculate forwarding pointers via a linear scan over the heap

COMPACT

public static final short COMPACT

Perform compaction via a linear scan over the heap

mcCollection

public short mcCollection

This is the phase that is executed to perform a mark-compact collection. FIXME: Far too much duplication and inside knowledge of StopTheWorld

markTrace

public final Trace markTrace

This trace sets the mark bit in live objects

forwardTrace

public final Trace forwardTrace

This trace updates pointers with the forwarded references

Constructor Detail

MC

public MC()

Constructor.

Method Detail

collectionPhase

public final void collectionPhase(short phaseId)

Perform a (global) collection phase.

Overrides:

collectionPhase in class Simple

Parameters:

phaseId - The unique id of the phase to perform.

getPagesUsed

public int getPagesUsed()

Return the number of pages reserved for use given the pending allocation. The superclass accounts for its spaces, we just augment this with the mark-sweep space's contribution.

Overrides:

getPagesUsed in class Plan

Returns:

The number of pages reserved given the pending allocation, excluding space reserved for copying.

willNeverMove

public boolean willNeverMove(ObjectReference object)

Description copied from class: Plan

Can this object ever move. Used by the VM to make decisions about whether it needs to copy IO buffers etc.

Overrides:

willNeverMove in class Plan

Parameters:

object - The object in question

Returns:

true if it is not possible that the object will ever move.

sanityExpectedRC

public int sanityExpectedRC(ObjectReference object,
                            int sanityRootRC)

Description copied from class: Plan

Return the expected reference count. For non-reference counting collectors this becomes a true/false relationship.

Overrides:

sanityExpectedRC in class Plan

Parameters:

object - The object to check.

sanityRootRC - The number of root references to the object.

Returns:

The expected (root excluded) reference count.

registerSpecializedMethods

protected void registerSpecializedMethods()

Description copied from class: Plan

Registers specialized methods.

Overrides:

registerSpecializedMethods in class Plan