org.mmtk.policy

Class MarkCompactCollector

java.lang.Object

org.mmtk.policy.MarkCompactCollector

public final class MarkCompactCollector
extends Object

This class implements unsynchronized (local) per-collector-thread elements of a sliding mark-compact collector.

Specifically, this class provides the methods that

• Calculate the forwarding pointers for heap objects, in a linear pass over (part of) the heap
• Performs the compaction pass over the heap.

Each collector thread maintains a private list of the pages that it compacts. If it runs out of work during the calculateForwardingPointers pass, it requests a new region from the global MarkCompactSpace. Regions compacted by a collector remain local to the collector.

See Also:

MarkCompactSpace, MarkCompactLocal

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private static class	MarkCompactCollector.FromCursor Subclass for the read-only cursor that leads the scan of regions.
private static class	MarkCompactCollector.RegionCursor Both the 'compact' and 'calculate' phases can be thought of as sweeping a pair of cursors across a linked list of regions.
private static class	MarkCompactCollector.ToCursor Subclass for the read-only cursor that follows the 'from' cursor, writing or calculating the position of copied objects

Field Summary

Fields

Modifier and Type	Field and Description
private MarkCompactCollector.FromCursor	fromCursor
private Address	regions This collector's work list
private MarkCompactSpace	space
private MarkCompactCollector.ToCursor	toCursor
(package private) static boolean	VERBOSE
(package private) static boolean	VERY_VERBOSE

Constructor Summary

Constructors

Constructor and Description
MarkCompactCollector(MarkCompactSpace space) Constructor

Method Summary

Modifier and Type	Method and Description
void	calculateForwardingPointers() Perform a linear scan through the objects allocated by this bump pointer, calculating where each live object will be post collection.
void	compact() Perform the compacting phase of the collection.

Methods inherited from class java.lang.Object

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

Field Detail

VERBOSE

static final boolean VERBOSE

See Also:

Constant Field Values

VERY_VERBOSE

static final boolean VERY_VERBOSE

See Also:

Constant Field Values

space

private final MarkCompactSpace space

regions

private Address regions

This collector's work list

fromCursor

private final MarkCompactCollector.FromCursor fromCursor

toCursor

private final MarkCompactCollector.ToCursor toCursor

Constructor Detail

MarkCompactCollector

public MarkCompactCollector(MarkCompactSpace space)

Constructor

Parameters:

space - The space to bump point into.

Method Detail

calculateForwardingPointers

public void calculateForwardingPointers()

Perform a linear scan through the objects allocated by this bump pointer, calculating where each live object will be post collection.

We maintain two cursors, fromCursor and toCursor, and simulate copying live objects from the former to the latter. Initially, the cursors point to the first region in this collector's local list, and increment in lockstep until the first dead object is encountered. After that, the to cursor trails the from cursor.

The outer loop advances the 'from' pointer

compact

public void compact()

Perform the compacting phase of the collection.