/*
* This file is part of the Jikes RVM project (http://jikesrvm.org).
*
* This file is licensed to You under the Eclipse Public License (EPL);
* You may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.opensource.org/licenses/eclipse-1.0.php
*
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership.
*/
package org.mmtk.policy;
import org.mmtk.plan.markcompact.MC;
import org.mmtk.utility.Log;
import org.mmtk.utility.alloc.Allocator;
import org.mmtk.utility.alloc.BumpPointer;
import org.mmtk.vm.VM;
import org.vmmagic.pragma.Inline;
import org.vmmagic.pragma.Uninterruptible;
import org.vmmagic.unboxed.Address;
import org.vmmagic.unboxed.Extent;
import org.vmmagic.unboxed.ObjectReference;
/**
* 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 MarkCompactSpace
* @see MarkCompactLocal
*/
@Uninterruptible
public final class MarkCompactCollector {
static final boolean VERBOSE = false;
static final boolean VERY_VERBOSE = VERBOSE && false;
private final MarkCompactSpace space;
/**
* This collector's work list
*/
private Address regions = Address.zero();
private final FromCursor fromCursor = new FromCursor();
private final ToCursor toCursor = new ToCursor();
/**
* Constructor
*
* @param space The space to bump point into.
*/
public MarkCompactCollector(MarkCompactSpace space) {
this.space = space;
}
/* ********************************************************************************
*
* Cursor classes
*
*/
/**
* Both the 'compact' and 'calculate' phases can be thought of as sweeping
* a pair of cursors across a linked list of regions. Each cursor requires
* maintaining pointers to the current region, the current address and the end of
* the region. The regionCursor class maintains these 3 pointers, while the
* subclasses ToCursor and FromCursor provide methods specific to the
* read and write pointers.
*/
@Uninterruptible
private abstract static class RegionCursor {
/** Name of the cursor - for debugging messages */
private final String name;
/**
* The current region, or zero if the cursor is invalid (eg after advancing
* past the end of the current work list
*/
protected Address region;
/**
* The limit of the current region. When reading a populated region, this is the
* address of the last used byte. When writing to a fresh region, this is the last
* byte in the region.
*/
protected Address limit;
/** The current address */
protected Address cursor;
/**
* @param name The name of the region - for debugging messages.
*/
public RegionCursor(String name) {
this.name = name;
}
/**
* Hook to allow subclasses to initialize the cursor in different ways.
*
* @param region The region to be processed.
*/
abstract void init(Address region);
/**
* Assert that the cursor is within the bounds of the region. Calls to this
* must be guarded by {@code if (VM.VERIFY_ASSERTIONS)}
*/
protected void assertCursorInBounds() {
VM.assertions._assert(!region.isZero());
VM.assertions._assert(cursor.GE(BumpPointer.getDataStart(region)),
"Cursor is below start of region");
VM.assertions._assert(cursor.LE(limit),"Cursor beyond end of region");
}
/**
* Increment the cursor.
* @param size Bytes to increment by
*/
void inc(int size) {
this.cursor = cursor.plus(size);
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
}
/**
* Increment the cursor to a specific address
* @param cursor Destination address
*/
public void incTo(Address cursor) {
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(cursor.GE(this.cursor));
this.cursor = cursor;
}
/**
* @param other Other region
* @return {@code true} if this cursor points to the same region as {@code other}
*/
boolean sameRegion(RegionCursor other) {
return region.EQ(other.getRegion());
}
/**
* @param size Size in bytes
* @return {@code true} if {@code size} bytes are available in the current region
*/
boolean isAvailable(int size) {
return cursor.plus(size).LE(limit);
}
/**
* @return The current cursor
*/
public Address get() {
return cursor;
}
/**
* @return The current region pointer
*/
public Address getRegion() {
return region;
}
/**
* @return The current region limit
*/
public Address getLimit() {
return limit;
}
/**
* Follow the linked-list of regions to the next region.
*/
void advanceToNextRegion() {
Address nextRegion = MarkCompactLocal.getNextRegion(region);
if (nextRegion.isZero()) {
region = Address.zero();
} else {
init(nextRegion);
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
}
}
/**
* @return {@code true} if we haven't advanced beyond the end of the region list
*/
boolean isValid() {
return !region.isZero();
}
/**
* @param ref The object in question
* @return {@code true} if the object's start address is in this region
*/
@Inline
boolean isInRegion(ObjectReference ref) {
Address addr = VM.objectModel.refToAddress(ref);
return addr.GE(BumpPointer.getDataStart(region)) && addr.LE(limit);
}
/**
* Print the cursor - for debugging
*/
void print() {
Log.write(name); Log.write(" cursor:");
Log.write(" region="); Log.write(region);
Log.write(" limit="); Log.write(limit);
Log.write(" cursor="); Log.write(cursor);
Log.writeln();
}
}
/**
* Subclass for the read-only cursor that leads the scan of regions.
*/
@Uninterruptible
private static final class FromCursor extends RegionCursor {
public FromCursor() {
super("from");
}
/**
* Initialize the cursor - the limit is the end of the allocated data
*/
@Override
void init(Address region) {
if (VM.VERIFY_ASSERTIONS) BumpPointer.checkRegionMetadata(region);
this.region = region;
this.cursor = MarkCompactLocal.getDataStart(region);
this.limit = MarkCompactLocal.getDataEnd(region);
}
/**
* Advance from the cursor to the start of the next object.
* @return The object reference of the next object.
*/
@Inline
ObjectReference advanceToObject() {
ObjectReference current = VM.objectModel.getObjectFromStartAddress(cursor);
cursor = VM.objectModel.objectStartRef(current);
if (VM.VERIFY_ASSERTIONS) {
Address lowBound = BumpPointer.getDataStart(region);
VM.assertions._assert(cursor.GE(lowBound) && cursor.LE(limit),"Cursor outside region");
}
return current;
}
/**
* Advance the cursor to the end of the given object.
* @return The object reference of the next object.
*/
@Inline
void advanceToObjectEnd(ObjectReference current) {
cursor = VM.objectModel.getObjectEndAddress(current);
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
}
/**
* Advance the cursor either to the next region in the list,
* or to a new region allocated from the global list.
* @param m
*/
void advanceToNextForwardableRegion(MarkCompactSpace space) {
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(get().EQ(getLimit()));
Address nextRegion = BumpPointer.getNextRegion(region);
if (nextRegion.isZero()) {
nextRegion = space.getNextRegion();
if (nextRegion.isZero()) {
region = Address.zero();
return;
}
MarkCompactLocal.setNextRegion(region,nextRegion);
MarkCompactLocal.clearNextRegion(nextRegion);
}
init(nextRegion);
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
}
/**
* Override the superclass with an additional assertion - we only advance
* when we have read to the end, and the cursor must point *precisely*
* to the last allocated byte in the region.
*/
@Override
void advanceToNextRegion() {
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(get().EQ(getLimit()));
super.advanceToNextRegion();
}
/**
* @return {@code true} if there are more objects in this region
*/
boolean hasMoreObjects() {
return cursor.LT(limit);
}
}
/**
* Subclass for the read-only cursor that follows the 'from' cursor,
* writing or calculating the position of copied objects
*/
@Uninterruptible
private static final class ToCursor extends RegionCursor {
public ToCursor() {
super("to");
}
/**
* Initialize the cursor to a given region. The limit is the limit of
* available space in the region.
*/
@Override
void init(Address region) {
if (VM.VERIFY_ASSERTIONS) BumpPointer.checkRegionMetadata(region);
this.region = region;
this.cursor = MarkCompactLocal.getDataStart(region);
this.limit = MarkCompactLocal.getRegionLimit(region);
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
}
/**
* Update the metadata of the current region with the current value
* of the cursor. Zero the region from here to the end.
*/
void finish() {
if (VM.VERIFY_ASSERTIONS) assertCursorInBounds();
Extent zeroBytes = limit.diff(cursor).toWord().toExtent();
VM.memory.zero(cursor, zeroBytes);
MarkCompactLocal.setDataEnd(region, cursor);
MarkCompactLocal.checkRegionMetadata(region);
}
/**
* Terminate the list of regions here.
* @return The address of the (old) next region in the list.
*/
Address snip() {
Address nextRegion = BumpPointer.getNextRegion(region);
BumpPointer.clearNextRegion(region);
finish();
return nextRegion;
}
/**
* Copy an object to an address within this cursor's region.
* @param from The source object
* @param to The target object
*/
@Inline
void copy(ObjectReference from, ObjectReference to) {
if (VM.VERIFY_ASSERTIONS) {
VM.assertions._assert(MarkCompactSpace.getForwardingPointer(from).toAddress().EQ(to.toAddress()));
VM.assertions._assert(cursor.GT(region) && cursor.LE(limit));
}
Address savedCursor = Address.zero();
if (VM.VERIFY_ASSERTIONS) savedCursor = cursor;
cursor = VM.objectModel.copyTo(from, to, cursor);
if (VM.VERIFY_ASSERTIONS) {
if (cursor.LT(BumpPointer.getDataStart(region)) || cursor.GT(limit)) {
Log.write("Copy of "); Log.write(from);
Log.write(" to "); Log.write(to);
Log.write(" puts cursor at "); Log.write(cursor);
Log.write(" (was: "); Log.write(savedCursor);
Log.writeln(")");
}
VM.assertions._assert(cursor.GT(region) && cursor.LE(limit));
}
MarkCompactSpace.setForwardingPointer(to, ObjectReference.nullReference());
if (VM.VERIFY_ASSERTIONS)
VM.assertions._assert(VM.objectModel.getObjectEndAddress(to).LE(limit));
}
/**
* Move to the next region, updating the metadata with the current 'write' state.
*/
void finishAndAdvanceToNextRegion() {
finish();
advanceToNextRegion();
}
/**
* Move to the next region, in read-only mode. Add the assertion of validity,
* since we shouldn't be able to fall off the end of the list while writing.
*/
@Override
void advanceToNextRegion() {
super.advanceToNextRegion();
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(isValid());
}
}
/* ***************************************************************************************** */
/**
* 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, {@code fromCursor} and {@code 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
*/
public void calculateForwardingPointers() {
if (regions.isZero()) {
regions = space.getNextRegion();
}
if (regions.isZero())
return;
fromCursor.init(regions);
toCursor.init(regions);
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(true);
/* Loop through active regions or until the last region */
while (fromCursor.isValid()) {
if (VERBOSE) {
fromCursor.print();
toCursor.print();
}
/* Loop through the objects in the current 'from' region */
while (fromCursor.hasMoreObjects()) {
ObjectReference current = fromCursor.advanceToObject();
fromCursor.advanceToObjectEnd(current);
if (MarkCompactSpace.toBeCompacted(current)) {
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(MarkCompactSpace.getForwardingPointer(current).isNull());
// Fake - allocate it.
int size = VM.objectModel.getSizeWhenCopied(current);
int align = VM.objectModel.getAlignWhenCopied(current);
int offset = VM.objectModel.getAlignOffsetWhenCopied(current);
// Move to the (aligned) start of the next object
toCursor.incTo(Allocator.alignAllocationNoFill(toCursor.get(), align, offset));
/*
* If we're allocating into separate regions, and we've allocated beyond the end of the
* current region, advance to the next one. We always allocate into regions we have
* scanned in this collector.
*/
if (!toCursor.sameRegion(fromCursor) && !toCursor.isAvailable(size)) {
// The 'to' pointer always trails the 'from' pointer, guaranteeing that
// there's a next region to advance to.
toCursor.advanceToNextRegion();
toCursor.incTo(Allocator.alignAllocationNoFill(toCursor.get(), align, offset));
}
ObjectReference target = VM.objectModel.getReferenceWhenCopiedTo(current, toCursor.get());
if (toCursor.sameRegion(fromCursor) && target.toAddress().GE(current.toAddress())) {
// Don't move the object.
MarkCompactSpace.setForwardingPointer(current, current);
toCursor.incTo(VM.objectModel.getObjectEndAddress(current));
} else {
MarkCompactSpace.setForwardingPointer(current, target);
toCursor.inc(size);
}
}
}
fromCursor.advanceToNextForwardableRegion(space);
}
}
/**
* Perform the compacting phase of the collection.
*/
public void compact() {
if (regions.isZero()) return;
toCursor.init(regions);
fromCursor.init(regions);
/* Loop through active regions or until the last region */
while (fromCursor.isValid()) {
if (VERBOSE) {
Log.write("Compacting from region "); Log.write(fromCursor.getRegion());
Log.write(" to region "); Log.writeln(toCursor.getRegion());
}
/* Loop through the objects in the region */
while (fromCursor.hasMoreObjects()) {
ObjectReference current = fromCursor.advanceToObject();
fromCursor.advanceToObjectEnd(current);
ObjectReference copyTo = MarkCompactSpace.getForwardingPointer(current);
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!copyTo.toAddress().EQ(Address.fromIntZeroExtend(VM.ALIGNMENT_VALUE)));
if (!copyTo.isNull() && Space.isInSpace(MC.MARK_COMPACT, copyTo)) {
if (VM.VERIFY_ASSERTIONS) {
if (MarkCompactSpace.isMarked(current)) {
Log.write("Object "); Log.write(current);
Log.writeln(" is marked during the compact phase");
}
VM.assertions._assert(!MarkCompactSpace.isMarked(current));
}
if (!toCursor.isInRegion(copyTo)) {
// Update metadata and move on
toCursor.finishAndAdvanceToNextRegion();
}
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(toCursor.isInRegion(copyTo));
toCursor.copy(current, copyTo);
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(toCursor.isInRegion(copyTo));
MarkCompactSpace.setForwardingPointer(copyTo, ObjectReference.nullReference());
}
}
fromCursor.advanceToNextRegion();
}
/* Fix up the last object pointer etc */
toCursor.finish();
/*
* Return unused pages to the global page resource
*/
Address region = toCursor.snip();
while (!region.isZero()) {
Address nextRegion = MarkCompactLocal.getNextRegion(region);
space.release(region);
region = nextRegion;
}
}
}