/**
* Copy numbytes from src to dst. Assumption either the ranges are non overlapping, or src >= dst
* + 4. Also, src and dst are 4 byte aligned and numBytes is a multiple of 4.
*
* @param dst the destination addr
* @param src the source addr
* @param numBytes the number of bytes top copy
*/
@Inline
public static void aligned32Copy(Address dst, Address src, Offset numBytes) {
if (USE_NATIVE && numBytes.sGT(Offset.fromIntSignExtend(NATIVE_THRESHOLD))) {
memcopy(dst, src, numBytes.toWord().toExtent());
} else {
if (VM.BuildFor64Addr) {
Word wordMask = Word.one().lsh(LOG_BYTES_IN_ADDRESS).minus(Word.one());
Word srcAlignment = src.toWord().and(wordMask);
if (srcAlignment.EQ(dst.toWord().and(wordMask))) {
Offset i = Offset.zero();
if (srcAlignment.EQ(Word.fromIntZeroExtend(BYTES_IN_INT))) {
dst.store(src.loadInt(i), i);
i = i.plus(BYTES_IN_INT);
}
Word endAlignment =
srcAlignment.plus(numBytes).and(Word.fromIntSignExtend(BYTES_IN_ADDRESS - 1));
numBytes = numBytes.minus(endAlignment.toOffset());
for (; i.sLT(numBytes); i = i.plus(BYTES_IN_ADDRESS)) {
dst.store(src.loadWord(i), i);
}
if (!endAlignment.isZero()) {
dst.store(src.loadInt(i), i);
}
return;
}
}
// normal case: 32 bit or (64 bit not aligned)
for (Offset i = Offset.zero(); i.sLT(numBytes); i = i.plus(BYTES_IN_INT)) {
dst.store(src.loadInt(i), i);
}
}
}
/** Each instance of this class corresponds to one explicitly managed large object space. */
@Uninterruptible
public final class LargeObjectSpace extends BaseLargeObjectSpace {
/**
* **************************************************************************
*
* <p>Class variables
*/
public static final int LOCAL_GC_BITS_REQUIRED = 2;
public static final int GLOBAL_GC_BITS_REQUIRED = 0;
private static final Word MARK_BIT = Word.one(); // ...01
private static final Word NURSERY_BIT = Word.fromIntZeroExtend(2); // ...10
private static final Word LOS_BIT_MASK = Word.fromIntZeroExtend(3); // ...11
/**
* **************************************************************************
*
* <p>Instance variables
*/
private Word markState;
private boolean inNurseryGC;
private final Treadmill treadmill;
/**
* **************************************************************************
*
* <p>Initialization
*/
/**
* The caller specifies the region of virtual memory to be used for this space. If this region
* conflicts with an existing space, then the constructor will fail.
*
* @param name The name of this space (used when printing error messages etc)
* @param pageBudget The number of pages this space may consume before consulting the plan
* @param vmRequest An object describing the virtual memory requested.
*/
public LargeObjectSpace(String name, int pageBudget, VMRequest vmRequest) {
super(name, pageBudget, vmRequest);
treadmill = new Treadmill(LOG_BYTES_IN_PAGE, true);
markState = Word.zero();
}
/**
* **************************************************************************
*
* <p>Collection
*/
/**
* Prepare for a new collection increment. For the mark-sweep collector we must flip the state of
* the mark bit between collections.
*/
public void prepare(boolean fullHeap) {
if (fullHeap) {
if (VM.VERIFY_ASSERTIONS) {
VM.assertions._assert(treadmill.fromSpaceEmpty());
}
markState = MARK_BIT.minus(markState);
}
treadmill.flip(fullHeap);
inNurseryGC = !fullHeap;
}
/**
* A new collection increment has completed. For the mark-sweep collector this means we can
* perform the sweep phase.
*/
public void release(boolean fullHeap) {
// sweep the large objects
sweepLargePages(true); // sweep the nursery
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(treadmill.nurseryEmpty());
if (fullHeap) sweepLargePages(false); // sweep the mature space
}
/** Sweep through the large pages, releasing all superpages on the "from space" treadmill. */
private void sweepLargePages(boolean sweepNursery) {
while (true) {
Address cell = sweepNursery ? treadmill.popNursery() : treadmill.pop();
if (cell.isZero()) break;
release(getSuperPage(cell));
}
if (VM.VERIFY_ASSERTIONS)
VM.assertions._assert(sweepNursery ? treadmill.nurseryEmpty() : treadmill.fromSpaceEmpty());
}
/**
* Release a group of pages that were allocated together.
*
* @param first The first page in the group of pages that were allocated together.
*/
@Inline
public void release(Address first) {
((FreeListPageResource) pr).releasePages(first);
}
/**
* **************************************************************************
*
* <p>Object processing and tracing
*/
/**
* Trace a reference to an object under a mark sweep collection policy. If the object header is
* not already marked, mark the object in either the bitmap or by moving it off the treadmill, and
* enqueue the object for subsequent processing. The object is marked as (an atomic) side-effect
* of checking whether already marked.
*
* @param trace The trace being conducted.
* @param object The object to be traced.
* @return The object (there is no object forwarding in this collector, so we always return the
* same object: this could be a void method but for compliance to a more general interface).
*/
@Inline
public ObjectReference traceObject(TransitiveClosure trace, ObjectReference object) {
boolean nurseryObject = isInNursery(object);
if (!inNurseryGC || nurseryObject) {
if (testAndMark(object, markState)) {
internalMarkObject(object, nurseryObject);
trace.processNode(object);
}
}
return object;
}
/**
* @param object The object in question
* @return True if this object is known to be live (i.e. it is marked)
*/
@Inline
public boolean isLive(ObjectReference object) {
return testMarkBit(object, markState);
}
/**
* An object has been marked (identifiged as live). Large objects are added to the to-space
* treadmill, while all other objects will have a mark bit set in the superpage header.
*
* @param object The object which has been marked.
*/
@Inline
private void internalMarkObject(ObjectReference object, boolean nurseryObject) {
Address cell = VM.objectModel.objectStartRef(object);
Address node = Treadmill.midPayloadToNode(cell);
treadmill.copy(node, nurseryObject);
}
/**
* **************************************************************************
*
* <p>Header manipulation
*/
/**
* Perform any required initialization of the GC portion of the header.
*
* @param object the object ref to the storage to be initialized
* @param alloc is this initialization occuring due to (initial) allocation (true) or due to
* copying (false)?
*/
@Inline
public void initializeHeader(ObjectReference object, boolean alloc) {
Word oldValue = VM.objectModel.readAvailableBitsWord(object);
Word newValue = oldValue.and(LOS_BIT_MASK.not()).or(markState);
if (alloc) newValue = newValue.or(NURSERY_BIT);
if (Plan.NEEDS_LOG_BIT_IN_HEADER) newValue = newValue.or(Plan.UNLOGGED_BIT);
VM.objectModel.writeAvailableBitsWord(object, newValue);
Address cell = VM.objectModel.objectStartRef(object);
treadmill.addToTreadmill(Treadmill.midPayloadToNode(cell), alloc);
}
/**
* Atomically attempt to set the mark bit of an object. Return true if successful, false if the
* mark bit was already set.
*
* @param object The object whose mark bit is to be written
* @param value The value to which the mark bit will be set
*/
@Inline
private boolean testAndMark(ObjectReference object, Word value) {
Word oldValue, markBit;
do {
oldValue = VM.objectModel.prepareAvailableBits(object);
markBit = oldValue.and(inNurseryGC ? LOS_BIT_MASK : MARK_BIT);
if (markBit.EQ(value)) return false;
} while (!VM.objectModel.attemptAvailableBits(
object, oldValue, oldValue.and(LOS_BIT_MASK.not()).or(value)));
return true;
}
/**
* Return true if the mark bit for an object has the given value.
*
* @param object The object whose mark bit is to be tested
* @param value The value against which the mark bit will be tested
* @return True if the mark bit for the object has the given value.
*/
@Inline
private boolean testMarkBit(ObjectReference object, Word value) {
return VM.objectModel.readAvailableBitsWord(object).and(MARK_BIT).EQ(value);
}
/**
* Return true if the object is in the logical nursery
*
* @param object The object whose status is to be tested
* @return True if the object is in the logical nursery
*/
@Inline
private boolean isInNursery(ObjectReference object) {
return VM.objectModel.readAvailableBitsWord(object).and(NURSERY_BIT).EQ(NURSERY_BIT);
}
/**
* Return the size of the per-superpage header required by this system. In this case it is just
* the underlying superpage header size.
*
* @return The size of the per-superpage header required by this system.
*/
@Inline
protected int superPageHeaderSize() {
return Treadmill.headerSize();
}
/**
* Return the size of the per-cell header for cells of a given class size.
*
* @return The size of the per-cell header for cells of a given class size.
*/
@Inline
protected int cellHeaderSize() {
return 0;
}
/**
* This is the treadmill used by the large object space.
*
* <p>Note that it depends on the specific local in use whether this is being used.
*
* @return The treadmill associated with this large object space.
*/
public Treadmill getTreadmill() {
return this.treadmill;
}
}
/**
* This class implements tracing for a simple immortal collection policy. Under this policy all that
* is required is for the "collector" to propogate marks in a liveness trace. It does not actually
* collect. This class does not hold any state, all methods are static.
*
* <p>$Id: ImmortalSpace.java,v 1.18 2005/01/19 02:49:02 steveb-oss Exp $
*
* @author Perry Cheng
* @author <a href="http://cs.anu.edu.au/~Steve.Blackburn">Steve Blackburn</a>
* @version $Revision: 1.18 $
* @date $Date: 2005/01/19 02:49:02 $
*/
public final class ImmortalSpace extends Space implements Constants, Uninterruptible {
/**
* **************************************************************************
*
* <p>Class variables
*/
static final Word GC_MARK_BIT_MASK = Word.one();
public static Word immortalMarkState = Word.zero(); // when GC off, the initialization value
/**
* **************************************************************************
*
* <p>Initialization
*/
/**
* The caller specifies the region of virtual memory to be used for this space. If this region
* conflicts with an existing space, then the constructor will fail.
*
* @param name The name of this space (used when printing error messages etc)
* @param pageBudget The number of pages this space may consume before consulting the plan
* @param start The start address of the space in virtual memory
* @param bytes The size of the space in virtual memory, in bytes
*/
public ImmortalSpace(String name, int pageBudget, Address start, Extent bytes) {
super(name, false, true, start, bytes);
pr = new MonotonePageResource(pageBudget, this, start, extent);
}
/**
* Construct a space of a given number of megabytes in size.
*
* <p>The caller specifies the amount virtual memory to be used for this space <i>in
* megabytes</i>. If there is insufficient address space, then the constructor will fail.
*
* @param name The name of this space (used when printing error messages etc)
* @param pageBudget The number of pages this space may consume before consulting the plan
* @param mb The size of the space in virtual memory, in megabytes (MB)
*/
public ImmortalSpace(String name, int pageBudget, int mb) {
super(name, false, true, mb);
pr = new MonotonePageResource(pageBudget, this, start, extent);
}
/**
* Construct a space that consumes a given fraction of the available virtual memory.
*
* <p>The caller specifies the amount virtual memory to be used for this space <i>as a fraction of
* the total available</i>. If there is insufficient address space, then the constructor will
* fail.
*
* @param name The name of this space (used when printing error messages etc)
* @param pageBudget The number of pages this space may consume before consulting the plan
* @param frac The size of the space in virtual memory, as a fraction of all available virtual
* memory
*/
public ImmortalSpace(String name, int pageBudget, float frac) {
super(name, false, true, frac);
pr = new MonotonePageResource(pageBudget, this, start, extent);
}
/**
* Construct a space that consumes a given number of megabytes of virtual memory, at either the
* top or bottom of the available virtual memory.
*
* <p>The caller specifies the amount virtual memory to be used for this space <i>in
* megabytes</i>, and whether it should be at the top or bottom of the available virtual memory.
* If the request clashes with existing virtual memory allocations, then the constructor will
* fail.
*
* @param name The name of this space (used when printing error messages etc)
* @param pageBudget The number of pages this space may consume before consulting the plan
* @param mb The size of the space in virtual memory, in megabytes (MB)
* @param top Should this space be at the top (or bottom) of the available virtual memory.
*/
public ImmortalSpace(String name, int pageBudget, int mb, boolean top) {
super(name, false, true, mb, top);
pr = new MonotonePageResource(pageBudget, this, start, extent);
}
/**
* Construct a space that consumes a given fraction of the available virtual memory, at either the
* top or bottom of the available virtual memory.
*
* <p>The caller specifies the amount virtual memory to be used for this space <i>as a fraction of
* the total available</i>, and whether it should be at the top or bottom of the available virtual
* memory. If the request clashes with existing virtual memory allocations, then the constructor
* will fail.
*
* @param name The name of this space (used when printing error messages etc)
* @param pageBudget The number of pages this space may consume before consulting the plan
* @param frac The size of the space in virtual memory, as a fraction of all available virtual
* memory
* @param top Should this space be at the top (or bottom) of the available virtual memory.
*/
public ImmortalSpace(String name, int pageBudget, float frac, boolean top) {
super(name, false, true, frac, top);
pr = new MonotonePageResource(pageBudget, this, start, extent);
}
/**
* **************************************************************************
*
* <p>Object header manipulations
*/
/** test to see if the mark bit has the given value */
private static boolean testMarkBit(ObjectReference object, Word value) {
return !(ObjectModel.readAvailableBitsWord(object).and(value).isZero());
}
/** write the given value in the mark bit. */
private static void writeMarkBit(ObjectReference object, Word value) {
Word oldValue = ObjectModel.readAvailableBitsWord(object);
Word newValue = oldValue.and(GC_MARK_BIT_MASK.not()).or(value);
ObjectModel.writeAvailableBitsWord(object, newValue);
}
/** atomically write the given value in the mark bit. */
private static void atomicWriteMarkBit(ObjectReference object, Word value) {
while (true) {
Word oldValue = ObjectModel.prepareAvailableBits(object);
Word newValue = oldValue.and(GC_MARK_BIT_MASK.not()).or(value);
if (ObjectModel.attemptAvailableBits(object, oldValue, newValue)) break;
}
}
/**
* Used to mark boot image objects during a parallel scan of objects during GC Returns true if
* marking was done.
*/
private static boolean testAndMark(ObjectReference object, Word value) throws InlinePragma {
Word oldValue;
do {
oldValue = ObjectModel.prepareAvailableBits(object);
Word markBit = oldValue.and(GC_MARK_BIT_MASK);
if (markBit.EQ(value)) return false;
} while (!ObjectModel.attemptAvailableBits(object, oldValue, oldValue.xor(GC_MARK_BIT_MASK)));
return true;
}
/**
* Trace a reference to an object under an immortal collection policy. If the object is not
* already marked, enqueue the object for subsequent processing. The object is marked as (an
* atomic) side-effect of checking whether already marked.
*
* @param object The object to be traced.
*/
public final ObjectReference traceObject(ObjectReference object) throws InlinePragma {
if (testAndMark(object, immortalMarkState)) Plan.enqueue(object);
return object;
}
public static void postAlloc(ObjectReference object) throws InlinePragma {
writeMarkBit(object, immortalMarkState);
}
/**
* Prepare for a new collection increment. For the immortal collector we must flip the state of
* the mark bit between collections.
*/
public void prepare() {
immortalMarkState = GC_MARK_BIT_MASK.sub(immortalMarkState);
}
public void release() {}
/**
* Release an allocated page or pages. In this case we do nothing because we only release pages
* enmasse.
*
* @param start The address of the start of the page or pages
*/
public final void release(Address start) throws InlinePragma {
Assert._assert(false); // this policy only releases pages enmasse
}
public final boolean isLive(ObjectReference object) throws InlinePragma {
return true;
}
/**
* Returns if the object in question is currently thought to be reachable. This is done by
* comparing the mark bit to the current mark state. For the immortal collector reachable and live
* are different, making this method necessary.
*
* @param object The address of an object in immortal space to test
* @return True if <code>ref</code> may be a reachable object (e.g., having the current mark
* state). While all immortal objects are live, some may be unreachable.
*/
public static boolean isReachable(ObjectReference object) {
return (ObjectModel.readAvailableBitsWord(object).and(GC_MARK_BIT_MASK).EQ(immortalMarkState));
}
}
