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 "class.h"
#include "object.h"
#include "object_callbacks.h"
#include "thread.h"

namespace art {

namespace gc {

class ReferenceProcessor;
class ReferenceQueue;

}  // namespace gc

struct ReferenceOffsets;
struct ReferenceClassOffsets;
struct FinalizerReferenceOffsets;

namespace mirror {
class ReferenceClass;

// 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_);

  static ReferenceClass* GetJavaLangRefReference() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    CHECK(java_lang_ref_Reference_ != nullptr);
    return ReadBarrier::BarrierForRoot<mirror::ReferenceClass, kWithReadBarrier>(
        &java_lang_ref_Reference_);
  }
  static void SetClass(ReferenceClass* klass);
  static void ResetClass(void);
  static void VisitRoots(RootCallback* callback, void* arg);

 private:
  // Note: This avoids a read barrier, it should only be used by the GC.
  HeapReference<Object>* GetReferentReferenceAddr() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    return GetFieldObjectReferenceAddr<kDefaultVerifyFlags>(ReferentOffset());
  }

  // 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:

  static ReferenceClass* java_lang_ref_Reference_;

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

// Tightly coupled with the ReferenceProcessor to provide switch for slow/fast path. Consistency
// is maintained by ReferenceProcessor.
class MANAGED ReferenceClass : public Class {
 public:
  static MemberOffset DisableIntrinsicOffset() {
    return OFFSET_OF_OBJECT_MEMBER(ReferenceClass, disable_intrinsic_);
  }
  static MemberOffset SlowPathEnabledOffset() {
    return OFFSET_OF_OBJECT_MEMBER(ReferenceClass, slow_path_enabled_);
  }

  void Init() {
    disable_intrinsic_ = false;
    slow_path_enabled_ = false;
  }

  bool GetSlowPathEnabled() const {
    return slow_path_enabled_;
  }
  void SetSlowPathEnabled(bool enabled) {
    slow_path_enabled_ = enabled;
  }

 private:
  int32_t disable_intrinsic_;
  int32_t slow_path_enabled_;
  // allows runtime to safely enable/disable intrinsics fast path for benchmarking

  friend struct art::ReferenceClassOffsets;  // for verifying offset information
  DISALLOW_IMPLICIT_CONSTRUCTORS(ReferenceClass);
};

// 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_