com.oracle.svm.core.genscavenge

Class UnalignedHeapChunk

java.lang.Object

com.oracle.svm.core.genscavenge.UnalignedHeapChunk

public final class UnalignedHeapChunk
extends Object

An UnalignedHeapChunk holds exactly one Object.

An UnalignedHeapChunk does not have a way to map from a Pointer to (or into) the Object they contain to the UnalignedHeapChunk that contains them.

An Object in a UnalignedHeapChunk needs to have a bit set in its DynamicHub to identify it as an Object in a UnalignedHeapChunk, so things like write-barriers don't try to update meta-data. Also so things like the getEnclosingHeapChunk(Object) can tell that the object is in an UnalignedHeapChunk.

Only a slow-path allocation method is available for UnalignedHeapChunks. This is acceptable because UnalignedHeapChunks are for large objects, so the cost of initializing the object dwarfs the cost of slow-path allocation.

The Object in an UnalignedHeapChunk can be promoted from one Space to another by moving the UnalignedHeapChunk from one Space to the other, rather than copying the Object out of the HeapChunk in one Space and into a destination HeapChunk in the other Space. That saves some amount of copying cost for these large objects. An UnalignedHeapChunk is laid out:

 +=================+-------+-------------------------------------+
 | UnalignedHeader | Card  | Object                              |
 | Fields          | Table |                                     |
 +=================+-------+-------------------------------------+
 

The HeapChunk fields can be accessed as declared fields, but the card "table" and the location of the Object are just computed as Pointers. In this implementation, I am only implementing precise card remembered sets, so I only need one entry for the whole Object. But for consistency I am treating it as a 1-element table.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	UnalignedHeapChunk.TestingBackDoor
static interface	UnalignedHeapChunk.UnalignedHeader Additional fields beyond what is in HeapChunk.Header.

Method Summary

Modifier and Type	Method and Description
static org.graalvm.word.Pointer	allocateMemory(UnalignedHeapChunk.UnalignedHeader that, org.graalvm.word.UnsignedWord size) Allocate uninitialized memory within this AlignedHeapChunk.
static void	dirtyCardForObject(Object obj, boolean verifyOnly)
static org.graalvm.word.UnsignedWord	getCommittedObjectMemory(UnalignedHeapChunk.UnalignedHeader that)
static MemoryWalker.HeapChunkAccess<UnalignedHeapChunk.UnalignedHeader>	getMemoryWalkerAccess()
static org.graalvm.word.UnsignedWord	getOverhead()
static boolean	walkDirtyObjects(UnalignedHeapChunk.UnalignedHeader that, ObjectVisitor visitor, boolean clean)
static boolean	walkObjects(UnalignedHeapChunk.UnalignedHeader that, ObjectVisitor visitor)
static boolean	walkObjectsInline(UnalignedHeapChunk.UnalignedHeader that, ObjectVisitor visitor)

Methods inherited from class java.lang.Object

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

Method Detail

getOverhead

public static org.graalvm.word.UnsignedWord getOverhead()

allocateMemory

public static org.graalvm.word.Pointer allocateMemory(UnalignedHeapChunk.UnalignedHeader that,
                                                      org.graalvm.word.UnsignedWord size)

Allocate uninitialized memory within this AlignedHeapChunk.

walkObjects

public static boolean walkObjects(UnalignedHeapChunk.UnalignedHeader that,
                                  ObjectVisitor visitor)

walkObjectsInline

public static boolean walkObjectsInline(UnalignedHeapChunk.UnalignedHeader that,
                                        ObjectVisitor visitor)

dirtyCardForObject

public static void dirtyCardForObject(Object obj,
                                      boolean verifyOnly)

walkDirtyObjects

public static boolean walkDirtyObjects(UnalignedHeapChunk.UnalignedHeader that,
                                       ObjectVisitor visitor,
                                       boolean clean)

getCommittedObjectMemory

public static org.graalvm.word.UnsignedWord getCommittedObjectMemory(UnalignedHeapChunk.UnalignedHeader that)

getMemoryWalkerAccess

public static MemoryWalker.HeapChunkAccess<UnalignedHeapChunk.UnalignedHeader> getMemoryWalkerAccess()