com.oracle.svm.core.heap

Class DiscoverableReference

java.lang.Object

com.oracle.svm.core.heap.DiscoverableReference

Direct Known Subclasses:

FeebleReference

public class DiscoverableReference
extends Object

This class is the plumbing under java.lang.ref.Reference. Instances of this class are discovered by the collector and put on a list. The list can then be inspected to implement java.lang.ref.Reference-like operations. Instances of DiscoverableReference are treated specially by the collector.

• The "referent" field will *not* be followed during live object discovery. It is a Pointer, not an Object.
• During live object discovery, each DiscoverableReference will be added to the "discovered" list.
• If the object referenced by the referent field is not live at the end of a collection, the "referent" field will be set to null.
• If the object referenced by the referent field is live at the end of a collection, the referent field is updated if the object moved.
• If the object referenced by the referent field is live at the end of a collection, the DiscoverableReference will be removed from the discovered list.

After a collection, anyone who is interested can run down the discovered list and do something with each DiscoverableReference. On top of this, I think you could build PhantomReference and WeakReference classes by adding a getReferent() method that returned the referent as an Object. See FeebleReference and FeebleReferenceList. Reference classes that subsequently promote their referent (SoftReference and FinalReference) would be more complicated. All the state that is needed to build lists, etc., is allocated in the DiscoverableReference instances, because space can not be allocated for lists during a collection.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	DiscoverableReference.TestingBackDoor For testing and debugging.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	DiscoverableReference(Object referent) Constructor for sub-classes.

Method Summary

Modifier and Type	Method and Description
void	clean()
void	clear() Clear the referent.
boolean	getIsDiscovered()
DiscoverableReference	getNextDiscoverableReference() Read access to the next field.
org.graalvm.word.Pointer	getReferentPointer() Read access to the referent, as a Pointer.
DiscoverableReference	prependToDiscoveredReference(DiscoverableReference newNext) Push a DiscoverableReference onto the list.
void	setReferentPointer(org.graalvm.word.Pointer value) Write access to the referent, as a Pointer.

Methods inherited from class java.lang.Object

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

Constructor Detail

DiscoverableReference

protected DiscoverableReference(Object referent)

Constructor for sub-classes. Only sub-types of this base type should be constructed.

Parameters:

referent - The Object to be tracked by this DiscoverableReference.

Method Detail

prependToDiscoveredReference

public DiscoverableReference prependToDiscoveredReference(DiscoverableReference newNext)

Push a DiscoverableReference onto the list.

clear

public void clear()

Clear the referent.

getReferentPointer

public org.graalvm.word.Pointer getReferentPointer()

Read access to the referent, as a Pointer. This is the low-level access for the garbage collector, so no barriers are used.

setReferentPointer

public void setReferentPointer(org.graalvm.word.Pointer value)

Write access to the referent, as a Pointer. This is the low-level access for the garbage collector, so no barriers are used.

getNextDiscoverableReference

public DiscoverableReference getNextDiscoverableReference()

Read access to the next field. Must use ObjectAccess to read the field because it is written with ObjectAccess only.

getIsDiscovered

public boolean getIsDiscovered()

clean

public void clean()