com.oracle.svm.core.genscavenge

Class ObjectHeaderImpl

java.lang.Object

com.oracle.svm.core.heap.ObjectHeader

com.oracle.svm.core.genscavenge.ObjectHeaderImpl

public class ObjectHeaderImpl
extends ObjectHeader

The low-order 3 bits of an ObjectHeader are used to mark things about this object instance.

The bits have two major purposes: figuring out whether, and how, to copy an object during collections; and (in the CardRememberedSet heap) whether, and how, to maintain remembered sets on oop stores. Since oop stores are (I think) way more common than collections, in this set of bits I'm optimizing for distinguishing needing from not needing remembered set maintenance. On top of that, I have to be able to figure out whether, and how, to copy an object.

One constant through all of this is that objects created by the fast-path don't want to do anything with these bits, so the state 0 0 0 means whatever the fast-path allocation does.

A low-order 0 bit will mean that the object does not need any remembered set maintenance. That leaves me 2 bits to distinguish objects in aligned chunks from objects in unaligned chunks (both of which do move), from native image heap objects and system allocator objects (both of which don't move).

A low-order 1 bit will mean that the object does need remembered set maintenance. That leaves me 2 bits to distinguish objects in aligned chunks from object in unaligned chunks.

Since I need a bit pattern to mark forwarding pointers, I'll lump those with the bits that need remembered set maintenance.

With those guidelines, here are the interpretation of the bits.

Bit value	Remembered set	Storage	Details
0 0 0	No	Aligned	The default setting, used by objects allocated in the young space on the fast-path.
0 0 1	Yes	Aligned	Modest objects in the old space.
0 1 0	No	Unaligned	Used for large arrays in the young space.
0 1 1	Yes	Unaligned	Large arrays in the old space. I don't distinguish arrays of primitives from arrays of objects. There won't be any oop stores to the arrays of primitives.
1 0 0	No	System	Objects allocated by system allocators.
1 0 1	--	--	This value is unused.
1 1 0	No	native image	Objects allocated in the native image heap.
1 1 1	--	--	The upper bits are a forwarding pointer

Field Summary

Fields inherited from class com.oracle.svm.core.heap.ObjectHeader

BITS_CLEAR, BITS_MASK

Method Summary

Modifier and Type	Method and Description
static int	classifyHeader(org.graalvm.word.UnsignedWord header) Debugging: Classifies a header so I can decide how much to trust it.
org.graalvm.word.WordBase	formatHub(DynamicHub hub, boolean rememberedSet, boolean unaligned)
Object	getForwardedObject(org.graalvm.word.Pointer ptr) Extract a forwarded Object from a header.
org.graalvm.word.Pointer	getForwardingPointer(org.graalvm.word.Pointer objectPointer) Extract a forwarding Pointer from a header.
protected static org.graalvm.word.UnsignedWord	getHeaderBitsFromHeader(org.graalvm.word.UnsignedWord header) This method returns the header bits from a header that has already been read from an object.
protected static org.graalvm.word.UnsignedWord	getHeaderBitsFromHeaderCarefully(org.graalvm.word.UnsignedWord header)
static ObjectHeaderImpl	getObjectHeaderImpl()
static boolean	hasRememberedSet(org.graalvm.word.UnsignedWord header) Is this the header of an object with a remembered set?
protected static boolean	headerBitsEqual(org.graalvm.word.UnsignedWord headerBits, org.graalvm.word.UnsignedWord specifiedBits) Test if an object header has the specified bits.
protected void	installForwardingPointer(Object original, Object copy) Install in an Object, a forwarding pointer to a different Object.
protected boolean	isAlignedHeader(org.graalvm.word.UnsignedWord header)
protected boolean	isAlignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
boolean	isAlignedObject(Object o)
protected boolean	isBootImage(Object o)
protected boolean	isBootImageCarefully(Object o)
protected boolean	isBootImageHeaderBits(org.graalvm.word.UnsignedWord headerBits)
protected boolean	isCardRememberedSetAlignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
protected boolean	isCardRememberedSetUnalignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
static boolean	isConsumedHeapChunkZapped(org.graalvm.word.UnsignedWord header)
boolean	isForwardedHeader(org.graalvm.word.UnsignedWord header) Is this header a forwarding pointer?
protected boolean	isForwardedHeaderBits(org.graalvm.word.UnsignedWord headerBits) Is this header a forwarding pointer?
boolean	isHeapAllocated(Object o)
protected boolean	isHeapAllocatedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
static boolean	isHeapObjectUnaligned(org.graalvm.word.UnsignedWord header) Is this the header of an unaligned heap object? Note: the header can only be from a heap object.
boolean	isNonHeapAllocated(Object o)
boolean	isNonHeapAllocatedCarefully(Object o)
boolean	isNonHeapAllocatedHeader(org.graalvm.word.UnsignedWord header)
protected boolean	isNonHeapAllocatedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
protected boolean	isNoRememberedSetAlignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
protected boolean	isNoRememberedSetUnalignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
protected boolean	isPointerToForwardedObject(org.graalvm.word.Pointer p) Predicate on a Pointer to a header.
protected boolean	isPointerToForwardedObjectCarefully(org.graalvm.word.Pointer p)
static boolean	isProducedHeapChunkZapped(org.graalvm.word.UnsignedWord header)
protected boolean	isUnalignedHeader(org.graalvm.word.UnsignedWord header)
protected boolean	isUnalignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)
boolean	isUnalignedObject(Object o)
Log	objectHeaderToLog(Object obj, Log log) Log an object header.
static DynamicHub	readDynamicHubFromObjectCarefully(Object o)
protected static org.graalvm.word.UnsignedWord	readHeaderBitsFromObject(Object o) This method reads the header from the object and returns the header bits.
protected static org.graalvm.word.UnsignedWord	readHeaderBitsFromObjectCarefully(Object o) This method reads the header from the object and returns the header bits.
static org.graalvm.word.UnsignedWord	readHeaderFromObjectCarefully(Object o)
static org.graalvm.word.UnsignedWord	readHeaderFromPointerCarefully(org.graalvm.word.Pointer p)
long	setBootImageOnLong(long l) A special method for use during native image construction.
protected void	setCardRememberedSetAligned(Object o)
protected void	setCardRememberedSetUnaligned(Object o)
protected static void	setHeaderBitsOnObject(Object o, org.graalvm.word.UnsignedWord headerBits) Set the specified bits in the header of an object.
void	setUnaligned(Object o) Objects are aligned by default.
String	toStringFromHeader(org.graalvm.word.UnsignedWord header) Debugging.

Methods inherited from class com.oracle.svm.core.heap.ObjectHeader

clearBits, dynamicHubFromObjectHeader, getHubOffset, getReferenceSize, initializeHeaderOfNewObject, readDynamicHubFromObject, readHeaderFromObject, readHeaderFromPointer, toStringFromObject, writeHeaderToObject

Methods inherited from class java.lang.Object

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

Method Detail

getObjectHeaderImpl

public static ObjectHeaderImpl getObjectHeaderImpl()

isProducedHeapChunkZapped

public static boolean isProducedHeapChunkZapped(org.graalvm.word.UnsignedWord header)

isConsumedHeapChunkZapped

public static boolean isConsumedHeapChunkZapped(org.graalvm.word.UnsignedWord header)

readHeaderFromPointerCarefully

public static org.graalvm.word.UnsignedWord readHeaderFromPointerCarefully(org.graalvm.word.Pointer p)

readHeaderFromObjectCarefully

public static org.graalvm.word.UnsignedWord readHeaderFromObjectCarefully(Object o)

readDynamicHubFromObjectCarefully

public static DynamicHub readDynamicHubFromObjectCarefully(Object o)

formatHub

public org.graalvm.word.WordBase formatHub(DynamicHub hub,
                                           boolean rememberedSet,
                                           boolean unaligned)

isNoRememberedSetAlignedHeaderBits

protected boolean isNoRememberedSetAlignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

isNoRememberedSetUnalignedHeaderBits

protected boolean isNoRememberedSetUnalignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

isBootImage

protected boolean isBootImage(Object o)

isBootImageCarefully

protected boolean isBootImageCarefully(Object o)

isBootImageHeaderBits

protected boolean isBootImageHeaderBits(org.graalvm.word.UnsignedWord headerBits)

setBootImageOnLong

public long setBootImageOnLong(long l)

Description copied from class: ObjectHeader

A special method for use during native image construction.

Specified by:

setBootImageOnLong in class ObjectHeader

isCardRememberedSetAlignedHeaderBits

protected boolean isCardRememberedSetAlignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

setCardRememberedSetAligned

protected void setCardRememberedSetAligned(Object o)

isCardRememberedSetUnalignedHeaderBits

protected boolean isCardRememberedSetUnalignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

setCardRememberedSetUnaligned

protected void setCardRememberedSetUnaligned(Object o)

isForwardedHeaderBits

protected boolean isForwardedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

Is this header a forwarding pointer?

isForwardedHeader

public boolean isForwardedHeader(org.graalvm.word.UnsignedWord header)

Description copied from class: ObjectHeader

Is this header a forwarding pointer?

Specified by:

isForwardedHeader in class ObjectHeader

getForwardingPointer

public org.graalvm.word.Pointer getForwardingPointer(org.graalvm.word.Pointer objectPointer)

Extract a forwarding Pointer from a header.

Specified by:

getForwardingPointer in class ObjectHeader

getForwardedObject

public Object getForwardedObject(org.graalvm.word.Pointer ptr)

Extract a forwarded Object from a header.

Specified by:

getForwardedObject in class ObjectHeader

setUnaligned

public void setUnaligned(Object o)

Description copied from class: ObjectHeader

Objects are aligned by default. This marks them as unaligned.

Specified by:

setUnaligned in class ObjectHeader

isNonHeapAllocatedHeaderBits

protected boolean isNonHeapAllocatedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

isNonHeapAllocatedHeader

public boolean isNonHeapAllocatedHeader(org.graalvm.word.UnsignedWord header)

Specified by:

isNonHeapAllocatedHeader in class ObjectHeader

isNonHeapAllocated

public boolean isNonHeapAllocated(Object o)

Specified by:

isNonHeapAllocated in class ObjectHeader

isNonHeapAllocatedCarefully

public boolean isNonHeapAllocatedCarefully(Object o)

isHeapAllocated

public boolean isHeapAllocated(Object o)

Specified by:

isHeapAllocated in class ObjectHeader

isHeapAllocatedHeaderBits

protected boolean isHeapAllocatedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

isAlignedHeaderBits

protected boolean isAlignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

isAlignedHeader

protected boolean isAlignedHeader(org.graalvm.word.UnsignedWord header)

isAlignedObject

public boolean isAlignedObject(Object o)

Specified by:

isAlignedObject in class ObjectHeader

isUnalignedHeaderBits

protected boolean isUnalignedHeaderBits(org.graalvm.word.UnsignedWord headerBits)

isUnalignedHeader

protected boolean isUnalignedHeader(org.graalvm.word.UnsignedWord header)

isUnalignedObject

public boolean isUnalignedObject(Object o)

Specified by:

isUnalignedObject in class ObjectHeader

hasRememberedSet

public static boolean hasRememberedSet(org.graalvm.word.UnsignedWord header)

Is this the header of an object with a remembered set?

Parameters:

header - the full header to be examined.

Returns:

true if the object has a remembered set, false otherwise.

isHeapObjectUnaligned

public static boolean isHeapObjectUnaligned(org.graalvm.word.UnsignedWord header)

Is this the header of an unaligned heap object? Note: the header can only be from a heap object.

Parameters:

header - the full header to be examined.

Returns:

true if the object is unaligned, false otherwise.

installForwardingPointer

protected void installForwardingPointer(Object original,
                                        Object copy)

Install in an Object, a forwarding pointer to a different Object.

isPointerToForwardedObject

protected boolean isPointerToForwardedObject(org.graalvm.word.Pointer p)

Predicate on a Pointer to a header.

isPointerToForwardedObjectCarefully

protected boolean isPointerToForwardedObjectCarefully(org.graalvm.word.Pointer p)

toStringFromHeader

public String toStringFromHeader(org.graalvm.word.UnsignedWord header)

Debugging. But maybe not for use in Log messages that I expect to be optimized away.

Specified by:

toStringFromHeader in class ObjectHeader

readHeaderBitsFromObject

protected static org.graalvm.word.UnsignedWord readHeaderBitsFromObject(Object o)

This method reads the header from the object and returns the header bits.

readHeaderBitsFromObjectCarefully

protected static org.graalvm.word.UnsignedWord readHeaderBitsFromObjectCarefully(Object o)

This method reads the header from the object and returns the header bits.

getHeaderBitsFromHeader

protected static org.graalvm.word.UnsignedWord getHeaderBitsFromHeader(org.graalvm.word.UnsignedWord header)

This method returns the header bits from a header that has already been read from an object.

getHeaderBitsFromHeaderCarefully

protected static org.graalvm.word.UnsignedWord getHeaderBitsFromHeaderCarefully(org.graalvm.word.UnsignedWord header)

setHeaderBitsOnObject

protected static void setHeaderBitsOnObject(Object o,
                                            org.graalvm.word.UnsignedWord headerBits)

Set the specified bits in the header of an object.

headerBitsEqual

protected static boolean headerBitsEqual(org.graalvm.word.UnsignedWord headerBits,
                                         org.graalvm.word.UnsignedWord specifiedBits)

Test if an object header has the specified bits.

classifyHeader

public static int classifyHeader(org.graalvm.word.UnsignedWord header)

Debugging: Classifies a header so I can decide how much to trust it.

• Negative results fail in one way or another.
• Positive results mean the header was valid.

objectHeaderToLog

public Log objectHeaderToLog(Object obj,
                             Log log)

Log an object header.