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

All Implemented Interfaces:

Constants

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.

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

StickyMS

public StickyMS()

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

Register specialized methods.

Overrides:

registerSpecializedMethods in class MS