runtime/mirror/reference.h

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_RUNTIME_MIRROR_REFERENCE_H_
#define ART_RUNTIME_MIRROR_REFERENCE_H_

#include "object.h"

namespace art {

struct ReferenceOffsets;
struct FinalizerReferenceOffsets;

namespace mirror {

// C++ mirror of java.lang.ref.Reference
class MANAGED Reference : public Object {
 public:
  static MemberOffset PendingNextOffset() {
    return OFFSET_OF_OBJECT_MEMBER(Reference, pending_next_);
  }
  static MemberOffset QueueOffset() {
    return OFFSET_OF_OBJECT_MEMBER(Reference, queue_);
  }
  static MemberOffset QueueNextOffset() {
    return OFFSET_OF_OBJECT_MEMBER(Reference, queue_next_);
  }
  static MemberOffset ReferentOffset() {
    return OFFSET_OF_OBJECT_MEMBER(Reference, referent_);
  }

  template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
  Object* GetReferent() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    return GetFieldObjectVolatile<Object, kDefaultVerifyFlags, kReadBarrierOption>(
        ReferentOffset());
  }
  template<bool kTransactionActive>
  void SetReferent(Object* referent) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    SetFieldObjectVolatile<kTransactionActive>(ReferentOffset(), referent);
  }
  template<bool kTransactionActive>
  void ClearReferent() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    SetFieldObjectVolatile<kTransactionActive>(ReferentOffset(), nullptr);
  }

  // Volatile read/write is not necessary since the java pending next is only accessed from
  // the java threads for cleared references. Once these cleared references have a null referent,
  // we never end up reading their pending next from the GC again.
  Reference* GetPendingNext() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    return GetFieldObject<Reference>(PendingNextOffset());
  }
  template<bool kTransactionActive>
  void SetPendingNext(Reference* pending_next) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    SetFieldObject<kTransactionActive>(PendingNextOffset(), pending_next);
  }

  bool IsEnqueued() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    // Since the references are stored as cyclic lists it means that once enqueued, the pending
    // next is always non-null.
    return GetPendingNext() != nullptr;
  }

  bool IsEnqueuable() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);

 private:
  // Field order required by test "ValidateFieldOrderOfJavaCppUnionClasses".
  HeapReference<Reference> pending_next_;  // Note this is Java volatile:
  HeapReference<Object> queue_;  // Note this is Java volatile:
  HeapReference<Reference> queue_next_;  // Note this is Java volatile:
  HeapReference<Object> referent_;  // Note this is Java volatile:

  friend struct art::ReferenceOffsets;  // for verifying offset information
  DISALLOW_IMPLICIT_CONSTRUCTORS(Reference);
};

// C++ mirror of java.lang.ref.FinalizerReference
class MANAGED FinalizerReference : public Reference {
 public:
  static MemberOffset ZombieOffset() {
    return OFFSET_OF_OBJECT_MEMBER(FinalizerReference, zombie_);
  }

  template<bool kTransactionActive>
  void SetZombie(Object* zombie) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    return SetFieldObjectVolatile<kTransactionActive>(ZombieOffset(), zombie);
  }
  Object* GetZombie() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    return GetFieldObjectVolatile<Object>(ZombieOffset());
  }

 private:
  HeapReference<FinalizerReference> next_;
  HeapReference<FinalizerReference> prev_;
  HeapReference<Object> zombie_;

  friend struct art::FinalizerReferenceOffsets;  // for verifying offset information
  DISALLOW_IMPLICIT_CONSTRUCTORS(FinalizerReference);
};

}  // namespace mirror
}  // namespace art

#endif  // ART_RUNTIME_MIRROR_REFERENCE_H_