org.mmtk.plan.stickyms

Class StickyMS

java.lang.Object

org.mmtk.plan.Plan

org.mmtk.plan.Simple

org.mmtk.plan.StopTheWorld

org.mmtk.plan.marksweep.MS

org.mmtk.plan.stickyms.StickyMS

public class StickyMS
extends MS

This class implements the global state of a simple sticky mark bits collector, based a simple on mark-sweep collector. The sticky mark bits algorithm is due to Demmers et al. (http://doi.acm.org/10.1145/96709.96735), and allows generational collection to be performed in a non-moving heap by overloading the role of mark bits to also indicate whether an object is new (nursery) or not. Thus nursery objects are identified by a bit in their header, not by where they lie within the address space. While Demmers et al. did their work in a conservative collector, here we have an exact collector, so we can use a regular write barrier, and don't need to use page protection etc.

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 or in Jikes RVM, Processors). 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
boolean	collectWholeHeap will this collection collect the whole heap
(package private) static boolean	MAJOR_GC_ONLY If true then we only do full heap GCs---so we're like MarkSweep (+ write barrier)
SharedDeque	modPool Remset pool
boolean	nextGCWholeHeap will the next collection collect the whole heap?
(package private) static boolean	NURSERY_COLLECT_PLOS If true, then new PLOS objects are collected at each nursery GC
static int	SCAN_NURSERY

Fields inherited from class org.mmtk.plan.marksweep.MS

MARK_SWEEP, msSpace, msTrace, SCAN_MARK

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
StickyMS()

Method Summary

Modifier and Type	Method and Description
void	collectionPhase(short phaseId) Perform a (global) collection phase.
void	forceFullHeapCollection() Force the next collection to be full heap.
boolean	isCurrentGCNursery()
boolean	isLastGCFull()
void	printPreStats() Print pre-collection statistics.
protected void	registerSpecializedMethods() Registers specialized methods.
int	sanityExpectedRC(ObjectReference object, int sanityRootRC) Return the expected reference count.
void	userTriggeredGC() A user-triggered GC has been initiated.

Methods inherited from class org.mmtk.plan.marksweep.MS

getPagesUsed, willNeverMove

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, freeMemory, fullyBooted, gcInProgress, gcInProgressProper, getAllocationSite, getCollectionReserve, getPagesAvail, getPagesReserved, getSpecializedScanClass, getTotalPages, handleUserCollectionRequest, harnessBegin, harnessEnd, insertPhaseAfter, isEmergencyCollection, isInitialized, isInternalTriggeredCollection, isUserTriggeredCollection, lastCollectionFullHeap, lastCollectionWasExhaustive, loadObjectReference, logPoll, notifyExit, poll, preCollectorSpawn, printDetailedTiming, printPostStats, 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

NURSERY_COLLECT_PLOS

static final boolean NURSERY_COLLECT_PLOS

If true, then new PLOS objects are collected at each nursery GC

See Also:

Constant Field Values

MAJOR_GC_ONLY

static final boolean MAJOR_GC_ONLY

If true then we only do full heap GCs---so we're like MarkSweep (+ write barrier)

See Also:

Constant Field Values

SCAN_NURSERY

public static int SCAN_NURSERY

nextGCWholeHeap

public boolean nextGCWholeHeap

will the next collection collect the whole heap?

collectWholeHeap

public boolean collectWholeHeap

will this collection collect the whole heap

modPool

public final SharedDeque modPool

Remset pool

Constructor Detail

StickyMS

public StickyMS()

Method Detail

userTriggeredGC

public void userTriggeredGC()

A user-triggered GC has been initiated.

forceFullHeapCollection

public void forceFullHeapCollection()

Description copied from class: Plan

Force the next collection to be full heap.

Overrides:

forceFullHeapCollection in class Plan

collectionPhase

public final void collectionPhase(short phaseId)

Description copied from class: MS

Perform a (global) collection phase.

Overrides:

collectionPhase in class MS

Parameters:

phaseId - The unique id of the phase to perform.

printPreStats

public void printPreStats()

Print pre-collection statistics. In this class we prefix the output indicating whether the collection was full heap or not.

Overrides:

printPreStats in class Plan

isCurrentGCNursery

public final boolean isCurrentGCNursery()

Overrides:

isCurrentGCNursery in class Plan

Returns:

Is current GC only collecting objects allocated since last GC.

isLastGCFull

public final boolean isLastGCFull()

Returns:

Is last GC a full collection?

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 MS