/*
* 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.plan.generational;
import org.mmtk.plan.*;
import org.mmtk.policy.CopySpace;
import org.mmtk.policy.Space;
import org.mmtk.utility.deque.*;
import org.mmtk.utility.heap.Map;
import org.mmtk.utility.heap.VMRequest;
import org.mmtk.utility.Log;
import org.mmtk.utility.options.Options;
import org.mmtk.utility.sanitychecker.SanityChecker;
import org.mmtk.utility.statistics.*;
import org.mmtk.vm.Collection;
import org.mmtk.vm.VM;
import org.vmmagic.pragma.*;
import org.vmmagic.unboxed.*;
/**
* This abstract class implements the core functionality of generic
* two-generationa copying collectors. Nursery collections occur when
* either the heap is full or the nursery is full. The nursery size
* is determined by an optional command line argument. If undefined,
* the nursery size is "infinite", so nursery collections only occur
* when the heap is full (this is known as a flexible-sized nursery
* collector). Thus both fixed and flexible nursery sizes are
* supported. Full heap collections occur when the nursery size has
* dropped to a statically defined threshold,
* <code>NURSERY_THRESHOLD</code><p>
*
* See also Plan.java for general comments on local vs global plan
* classes.
*/
@Uninterruptible
public abstract class Gen extends StopTheWorld {
/*****************************************************************************
*
* Constants
*/
protected static final float SURVIVAL_ESTIMATE = 0.8f; // est yield
protected static final float MATURE_FRACTION = 0.5f; // est yield
private static final float WORST_CASE_COPY_EXPANSION = 1.5f; // worst case for addition of one word overhead due to address based hashing
public static final boolean IGNORE_REMSETS = false;
public static final boolean USE_NON_HEAP_OBJECT_REFERENCE_WRITE_BARRIER = false;
public static final boolean USE_OBJECT_BARRIER_FOR_AASTORE = false; // choose between slot and object barriers
public static final boolean USE_OBJECT_BARRIER_FOR_PUTFIELD = false; // choose between slot and object barriers
public static final boolean USE_OBJECT_BARRIER = USE_OBJECT_BARRIER_FOR_AASTORE || USE_OBJECT_BARRIER_FOR_PUTFIELD;
/** Fraction of available virtual memory to give to the nursery (if contiguous) */
protected static final float NURSERY_VM_FRACTION = 0.15f;
/** Switch between a contiguous and discontiguous nursery (experimental) */
static final boolean USE_DISCONTIGUOUS_NURSERY = false;
// Allocators
public static final int ALLOC_NURSERY = ALLOC_DEFAULT;
public static final int ALLOC_MATURE = StopTheWorld.ALLOCATORS + 1;
public static final int ALLOC_MATURE_MINORGC = StopTheWorld.ALLOCATORS + 2;
public static final int ALLOC_MATURE_MAJORGC = StopTheWorld.ALLOCATORS + 3;
public static final int SCAN_NURSERY = 0;
public static final int SCAN_MATURE = 1;
/*****************************************************************************
*
* Class fields
*/
/* Statistics */
protected static final BooleanCounter fullHeap = new BooleanCounter("majorGC", true, true);
private static final Timer fullHeapTime = new Timer("majorGCTime", false, true);
protected static final EventCounter wbFast;
protected static final EventCounter wbSlow;
public static final SizeCounter nurseryMark;
public static final SizeCounter nurseryCons;
/** The nursery space is where all new objects are allocated by default */
private static final VMRequest vmRequest = USE_DISCONTIGUOUS_NURSERY ? VMRequest.create() : VMRequest.create(NURSERY_VM_FRACTION, true);
public static final CopySpace nurserySpace = new CopySpace("nursery", DEFAULT_POLL_FREQUENCY, false, vmRequest);
public static final int NURSERY = nurserySpace.getDescriptor();
private static final Address NURSERY_START = nurserySpace.getStart();
/*****************************************************************************
*
* Instance fields
*/
/* status fields */
public boolean gcFullHeap = false;
public boolean nextGCFullHeap = false;
/* The trace object */
public final Trace nurseryTrace = new Trace(metaDataSpace);
/**
* Remset pools
*/
public final SharedDeque modbufPool = new SharedDeque("modBufs",metaDataSpace, 1);
public final SharedDeque remsetPool = new SharedDeque("remSets",metaDataSpace, 1);
public final SharedDeque arrayRemsetPool = new SharedDeque("arrayRemSets",metaDataSpace, 2);
/*
* Class initializer
*/
static {
if (GATHER_WRITE_BARRIER_STATS) {
wbFast = new EventCounter("wbFast");
wbSlow = new EventCounter("wbSlow");
} else {
wbFast = null;
wbSlow = null;
}
if (Stats.GATHER_MARK_CONS_STATS) {
nurseryMark = new SizeCounter("nurseryMark", true, true);
nurseryCons = new SizeCounter("nurseryCons", true, true);
} else {
nurseryMark = null;
nurseryCons = null;
}
}
/*****************************************************************************
*
* Collection
*/
/**
* Force the next collection to be full heap.
*/
public void forceFullHeapCollection() {
nextGCFullHeap = true;
}
/**
* Perform a (global) collection phase.
*
* @param phaseId Collection phase to execute.
*/
@NoInline
public void collectionPhase(short phaseId) {
if (phaseId == SET_COLLECTION_KIND) {
super.collectionPhase(phaseId);
gcFullHeap = requiresFullHeapCollection();
return;
}
if (phaseId == PREPARE) {
nurserySpace.prepare(true);
if (traceFullHeap()){
if (gcFullHeap) {
if (Stats.gatheringStats()) fullHeap.set();
fullHeapTime.start();
}
super.collectionPhase(phaseId);
// we can throw away the remsets (but not modbuf) for a full heap GC
remsetPool.clearDeque(1);
arrayRemsetPool.clearDeque(2);
}
return;
}
if (phaseId == CLOSURE) {
if (!traceFullHeap()) {
nurseryTrace.prepare();
}
return;
}
if (phaseId == RELEASE) {
nurserySpace.release();
modbufPool.clearDeque(1);
remsetPool.clearDeque(1);
arrayRemsetPool.clearDeque(2);
if (!traceFullHeap()) {
nurseryTrace.release();
} else {
super.collectionPhase(phaseId);
if (gcFullHeap) fullHeapTime.stop();
}
nextGCFullHeap = (getPagesAvail() < Options.nurserySize.getMinNursery());
return;
}
super.collectionPhase(phaseId);
}
/**
* This method controls the triggering of a GC. It is called periodically
* during allocation. Returns true to trigger a collection.
*
* @param spaceFull Space request failed, must recover pages within 'space'.
* @return True if a collection is requested by the plan.
*/
public final boolean collectionRequired(boolean spaceFull) {
int nurseryPages = nurserySpace.reservedPages();
if (nurseryPages > Options.nurserySize.getMaxNursery()) {
return true;
}
if (virtualMemoryExhausted())
return true;
return super.collectionRequired(spaceFull);
}
/**
* Determine if this GC should be a full heap collection.
*
* @return True is this GC should be a full heap collection.
*/
protected boolean requiresFullHeapCollection() {
if (collectionTrigger == Collection.EXTERNAL_GC_TRIGGER && Options.fullHeapSystemGC.getValue()) {
return true;
}
if (nextGCFullHeap || collectionAttempt > 1) {
// Forces full heap collection
return true;
}
if (loSpace.allocationFailed() ||
nonMovingSpace.allocationFailed() ||
(USE_CODE_SPACE && (largeCodeSpace.allocationFailed() || smallCodeSpace.allocationFailed()))) {
// We need space from the nursery
return true;
}
if (virtualMemoryExhausted())
return true;
int smallNurseryPages = nurserySpace.committedPages();
int smallNurseryYield = (int)((smallNurseryPages << 1) * SURVIVAL_ESTIMATE);
if (smallNurseryYield < getPagesRequired()) {
// Our total yield is insufficent.
return true;
}
if (nurserySpace.allocationFailed()) {
if (smallNurseryYield < (nurserySpace.requiredPages() << 1)) {
// We have run out of VM pages in the nursery
return true;
}
}
return false;
}
/**
* Independent of how many pages remain in the page budget (a function of
* heap size), we must ensure we never exhaust virtual memory. Therefore
* we must never let the nursery grow to the extent that it can't be
* copied into the mature space.
*
* @return True if the nursery has grown to the extent that it may not be
* able to be copied into the mature space.
*/
private boolean virtualMemoryExhausted() {
return ((int) (nurserySpace.reservedPages()*WORST_CASE_COPY_EXPANSION) >= getMaturePhysicalPagesAvail());
}
/*****************************************************************************
*
* Correctness
*/
/*****************************************************************************
*
* Accounting
*/
/**
* Return the number of pages in use given the pending
* allocation. Simply add the nursery's contribution to that of
* the superclass.
*
* @return The number of pages reserved given the pending
* allocation, excluding space reserved for copying.
*/
@Override
public int getPagesUsed() {
return (nurserySpace.reservedPages() + super.getPagesUsed());
}
/**
* Return the number of pages available for allocation, <i>assuming
* all future allocation is to the nursery</i>.
*
* @return The number of pages available for allocation, <i>assuming
* all future allocation is to the nursery</i>.
*/
@Override
public int getPagesAvail() {
return super.getPagesAvail() >> 1;
}
/**
* Return the number of pages reserved for copying.
*
* @return The number of pages reserved given the pending
* allocation, including space reserved for copying.
*/
@Override
public int getCollectionReserve() {
return nurserySpace.reservedPages() + super.getCollectionReserve();
}
/**
* Return the number of pages available for allocation into the mature
* space.
*
* @return The number of pages available for allocation into the mature
* space.
*/
public abstract int getMaturePhysicalPagesAvail();
/**
* Calculate the number of pages a collection is required to free to satisfy
* outstanding allocation requests.
*
* @return the number of pages a collection is required to free to satisfy
* outstanding allocation requests.
*/
@Override
public int getPagesRequired() {
/* We don't currently pretenure, so mature space must be zero */
return super.getPagesRequired() + (nurserySpace.requiredPages() << 1);
}
/*****************************************************************************
*
* Miscellaneous
*/
/**
* Return true if the address resides within the nursery
*
* @param addr The object to be tested
* @return true if the address resides within the nursery
*/
@Inline
static boolean inNursery(Address addr) {
if (USE_DISCONTIGUOUS_NURSERY)
return Map.getDescriptorForAddress(addr) == NURSERY;
else
return addr.GE(NURSERY_START);
}
/**
* Return true if the object resides within the nursery
*
* @param obj The object to be tested
* @return true if the object resides within the nursery
*/
@Inline
static boolean inNursery(ObjectReference obj) {
return inNursery(obj.toAddress());
}
/**
* @return Does the mature space do copying ?
*/
protected boolean copyMature() {
return false;
}
/**
* Print pre-collection statistics. In this class we prefix the output
* indicating whether the collection was full heap or not.
*/
public void printPreStats() {
if ((Options.verbose.getValue() >= 1) && (gcFullHeap))
Log.write("[Full heap]");
super.printPreStats();
}
/**
* @return The mature space, set by each subclass of <code>Gen</code>.
*/
protected abstract Space activeMatureSpace();
/**
* @return True if we should trace the whole heap during collection. True if
* we're ignorning remsets or if we're doing a full heap GC.
*/
public final boolean traceFullHeap() {
return IGNORE_REMSETS || gcFullHeap;
}
/**
* @return Is current GC only collecting objects allocated since last GC.
*/
public final boolean isCurrentGCNursery() {
return !gcFullHeap;
}
/**
* @return Is last GC a full collection?
*/
public final boolean lastCollectionFullHeap() {
return gcFullHeap;
}
/**
* @see org.mmtk.plan.Plan#willNeverMove
*
* @param object Object in question
* @return True if the object will never move
*/
@Override
public boolean willNeverMove(ObjectReference object) {
if (Space.isInSpace(NURSERY, object))
return false;
return super.willNeverMove(object);
}
/**
* Return the expected reference count. For non-reference counting
* collectors this becomes a true/false relationship.
*
* @param object The object to check.
* @param sanityRootRC The number of root references to the object.
* @return The expected (root excluded) reference count.
*/
public int sanityExpectedRC(ObjectReference object, int sanityRootRC) {
Space space = Space.getSpaceForObject(object);
// Nursery
if (space == Gen.nurserySpace) {
return SanityChecker.DEAD;
}
// Immortal spaces
if (space == Gen.immortalSpace || space == Gen.vmSpace) {
return space.isReachable(object) ? SanityChecker.ALIVE : SanityChecker.DEAD;
}
// Mature space (nursery collection)
if (VM.activePlan.global().isCurrentGCNursery()) {
return SanityChecker.UNSURE;
}
// Mature space (full heap collection)
return space.isReachable(object) ? SanityChecker.ALIVE : SanityChecker.DEAD;
}
/**
* Register specialized methods.
*/
@Interruptible
protected void registerSpecializedMethods() {
TransitiveClosure.registerSpecializedScan(SCAN_NURSERY, GenNurseryTraceLocal.class);
super.registerSpecializedMethods();
}
}