Delete own peer with a common class PhantomReference

Question

As Hans Boehm in the conversation "Google I / O '17" How to manage your own C ++ - memory in Android "offers to use PhantomReferenceto ensure the correct removal of their own peer nodes.

In a linked video for 18 min 57 sec, he shows an example of the implementation of an object registering itself in a class PhantomReferencefor its type. This class PhantomReference, then it shows 19 min 49 sec . So I copied his approach to my example. See below.

Although this approach works fine, it does not scale. I will need to create quite a few objects, and I have not found a way to create a base class (for my objects or PhantomReference) that will accept any objects and will correctly process its own deletion.

How to create a common base class PhantomReferencethat can call its own static method for the provided object?

I tried to convert generic PhantomReference, but the static static deletion method impedes implementation.

My WorkViewModel

import android.databinding.*;

public class WorkViewModel extends BaseObservable
{
  private long _nativeHandle;

  public WorkViewModel(Database database, int workId)
  {
    _nativeHandle = create(database.getNativeHandle(), workId);
    WorkViewModelPhantomReference.register(this, _nativeHandle);
  }

  private static native long create(long databaseHandle, int workId);
  static native void delete(long nativeHandle);

  @Bindable
  public native int getWorkId();
  public native void setWorkId(int workId);
}

My WorkViewModelPhantomReference

import java.lang.ref.*;
import java.util.*;

public class WorkViewModelPhantomReference extends PhantomReference<WorkViewModel>
{
  private static Set<WorkViewModelPhantomReference> phantomReferences = new HashSet<WorkViewModelPhantomReference>();
  private static ReferenceQueue<WorkViewModel> garbageCollectedObjectsQueue = new ReferenceQueue<WorkViewModel>();
  private long _nativeHandle;

  private WorkViewModelPhantomReference(WorkViewModel workViewModel, long nativeHandle)
  {
    super(workViewModel, garbageCollectedObjectsQueue);
    _nativeHandle = nativeHandle;
  }

  public static void register(WorkViewModel workViewModel, long nativeHandle)
  {
    phantomReferences.add(new WorkViewModelPhantomReference(workViewModel, nativeHandle));
  }

  public static void deleteOrphanedNativePeerObjects()
  {
    WorkViewModelPhantomReference reference;

    while((reference = (WorkViewModelPhantomReference)garbageCollectedObjectsQueue.poll()) != null)
    {
      WorkViewModel.delete(reference._nativeHandle);
      phantomReferences.remove(reference);
    }
  }
}

Answer 1

API- Java 9s Cleaner, , , PhantomReference, , . , static. , .. Cleanable, , , clear() clean() :

public class Cleaner {
    public interface Cleanable {
        void clean();
    }
    public static Cleanable register(Object o, Runnable r) {
        CleanerReference c = new CleanerReference(
                Objects.requireNonNull(o), Objects.requireNonNull(r));
        phantomReferences.add(c);
        return c;
    }
    private static final Set<CleanerReference> phantomReferences
                                             = ConcurrentHashMap.newKeySet();
    private static final ReferenceQueue<Object> garbageCollectedObjectsQueue
                                              = new ReferenceQueue<>();

    static final class CleanerReference extends PhantomReference<Object>
                                        implements Cleanable {
        private final Runnable cleaningAction;

        CleanerReference(Object referent, Runnable action) {
            super(referent, garbageCollectedObjectsQueue);
            cleaningAction = action;
        }
        public void clean() {
            if(phantomReferences.remove(this)) {
                super.clear();
                cleaningAction.run();
            }
        }
    }
    public static void deleteOrphanedNativePeerObjects() {
        CleanerReference reference;
        while((reference=(CleanerReference)garbageCollectedObjectsQueue.poll()) != null) {
            reference.clean();
        }
    }
}

Java 8; ConcurrentHashMap.newKeySet() , Collections.newSetFromMap(new ConcurrentHashMap<CleanerReference,Boolean>()).

deleteOrphanedNativePeerObjects(), , , , , , .

Runnable , Cleanable , , , .

public class WorkViewModel extends BaseObservable implements AutoCloseable
{
    private long _nativeHandle;
    Cleaner.Cleanable cleanable;

    public WorkViewModel(Database database, int workId)
    {
      _nativeHandle = create(database.getNativeHandle(), workId);
      cleanable = createCleanable(this, _nativeHandle);
    }
    private static Cleaner.Cleanable createCleanable(Object o, long _nativeHandle) {
        return Cleaner.register(o, () -> delete(_nativeHandle));
    }

    @Override
    public void close() {
        cleanable.clean();
    }

    private static native long create(long databaseHandle, int workId);
    static native void delete(long nativeHandle);

    @Bindable
    public native int getWorkId();
    public native void setWorkId(int workId);

}

AutoCloseable, try -with-resources, close() , . , , phantom Set , , . close() , .

, , , .

- , Runnable ; , phantom. , this, static . this , . Object, .