/* * This file is part of the Jikes RVM project (http://jikesrvm.org). * * This file is licensed to You under the Eclipse Public License (EPL); * You may not use this file except in compliance with the License. You * may obtain a copy of the License at * * http://www.opensource.org/licenses/eclipse-1.0.php * * See the COPYRIGHT.txt file distributed with this work for information * regarding copyright ownership. */ package java.lang.ref; import static org.jikesrvm.mm.mminterface.Barriers.NEEDS_OBJECT_GETFIELD_BARRIER; import static org.jikesrvm.mm.mminterface.Barriers.NEEDS_OBJECT_PUTFIELD_BARRIER; import org.jikesrvm.classloader.RVMType; import org.jikesrvm.mm.mminterface.Barriers; import org.jikesrvm.runtime.Magic; import org.vmmagic.pragma.Entrypoint; import org.vmmagic.pragma.Inline; import org.vmmagic.pragma.Uninterruptible; import org.vmmagic.pragma.ReferenceFieldsVary; import org.vmmagic.unboxed.Address; /** * The JikesRVM implementation of the java.lang.ref.Reference class. */ @ReferenceFieldsVary public abstract class Reference<T> { /** * The underlying object. This field is a Address so it will not * be automatically kept alive by the garbage collector.<p> * * Set and maintained by the ReferenceProcessor class. */ @Entrypoint private Address _referent; /** * Link to the next entry on the queue. If this is {@code null}, this * reference is not enqueued. Otherwise it points to the next * reference. The last reference on a queue will point to itself * (not to {@code null}, that value is used to mark a not enqueued * reference). This field and its semantics is defined by the * default implementation of java.lang.ref.ReferenceQueue in the GNU * classpath release. * @see java.lang.ref.ReferenceQueue */ Reference nextOnQueue; /** * The queue this reference is registered on. This is null, if this * wasn't registered to any queue or reference was already enqueued. */ ReferenceQueue<T> queue; Reference(T ref) { } Reference(T ref, ReferenceQueue<T> q) { if (q == null) throw new NullPointerException(); queue = q; } /** * Returns the object, this reference refers to. * @return the object, this reference refers to, or null if the * reference was cleared. */ @SuppressWarnings("unchecked") // This method requires an unchecked cast public T get() { return (T)getInternal(); } /** * Takes the passed address and (atomically) performs any read barrier actions * before returning it as an object. * * @param tmp The non-zero referent address * @return The referent object. */ @Uninterruptible @Inline Object getInternal() { if (RVMType.JavaLangRefReferenceReferenceField.madeTraced()) { if (NEEDS_OBJECT_GETFIELD_BARRIER) { return Barriers.objectFieldRead(this, RVMType.JavaLangRefReferenceReferenceField.getOffset(), RVMType.JavaLangRefReferenceReferenceField.getId()); } else { return Magic.getObjectAtOffset(this, RVMType.JavaLangRefReferenceReferenceField.getOffset(), RVMType.JavaLangRefReferenceReferenceField.getId()); } } else { Address tmp = _referent; if (tmp.isZero()) { return null; } else { Object ref = Magic.addressAsObject(tmp); if (Barriers.NEEDS_JAVA_LANG_REFERENCE_READ_BARRIER) { ref = Barriers.javaLangReferenceReadBarrier(ref); } return ref; } } } public void clear() { if (RVMType.JavaLangRefReferenceReferenceField.madeTraced()) { if (NEEDS_OBJECT_PUTFIELD_BARRIER) { Barriers.objectFieldWrite(this, null, RVMType.JavaLangRefReferenceReferenceField.getOffset(), RVMType.JavaLangRefReferenceReferenceField.getId()); } else { Magic.setObjectAtOffset(this, RVMType.JavaLangRefReferenceReferenceField.getOffset(), null, RVMType.JavaLangRefReferenceReferenceField.getId()); } } } public boolean isEnqueued() { return nextOnQueue != null; } /* * This method requires external synchronization. * The logically uninterruptible pragma is a bold faced lie; * injecting it for now to avoid a warning message during the build * that users might find confusing. We think the problem is actually * not a 'real' problem... * FIXME update comment */ public boolean enqueue() { if (nextOnQueue == null && queue != null) { queue.enqueue(this); queue = null; return true; } return false; } @Uninterruptible public final boolean enqueueInternal() { if (nextOnQueue == null && queue != null) { queue.enqueueInternal(this); queue = null; return true; } return false; } // TODO: Harmony void dequeue() { return; } }