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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ART_RUNTIME_MIRROR_OBJECT_REFERENCE_H_
     18 #define ART_RUNTIME_MIRROR_OBJECT_REFERENCE_H_
     19 
     20 #include "base/mutex.h"  // For Locks::mutator_lock_.
     21 #include "globals.h"
     22 
     23 namespace art {
     24 namespace mirror {
     25 
     26 class Object;
     27 
     28 // Classes shared with the managed side of the world need to be packed so that they don't have
     29 // extra platform specific padding.
     30 #define MANAGED PACKED(4)
     31 
     32 // Value type representing a reference to a mirror::Object of type MirrorType.
     33 template<bool kPoisonReferences, class MirrorType>
     34 class MANAGED ObjectReference {
     35  public:
     36   MirrorType* AsMirrorPtr() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     37     return UnCompress();
     38   }
     39 
     40   void Assign(MirrorType* other) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     41     reference_ = Compress(other);
     42   }
     43 
     44   void Clear() {
     45     reference_ = 0;
     46     DCHECK(IsNull());
     47   }
     48 
     49   bool IsNull() const {
     50     return reference_ == 0;
     51   }
     52 
     53   uint32_t AsVRegValue() const {
     54     return reference_;
     55   }
     56 
     57  protected:
     58   ObjectReference<kPoisonReferences, MirrorType>(MirrorType* mirror_ptr)
     59       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
     60       : reference_(Compress(mirror_ptr)) {
     61   }
     62 
     63   // Compress reference to its bit representation.
     64   static uint32_t Compress(MirrorType* mirror_ptr) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     65     uintptr_t as_bits = reinterpret_cast<uintptr_t>(mirror_ptr);
     66     return static_cast<uint32_t>(kPoisonReferences ? -as_bits : as_bits);
     67   }
     68 
     69   // Uncompress an encoded reference from its bit representation.
     70   MirrorType* UnCompress() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     71     uintptr_t as_bits = kPoisonReferences ? -reference_ : reference_;
     72     return reinterpret_cast<MirrorType*>(as_bits);
     73   }
     74 
     75   friend class Object;
     76 
     77   // The encoded reference to a mirror::Object.
     78   uint32_t reference_;
     79 };
     80 
     81 // References between objects within the managed heap.
     82 template<class MirrorType>
     83 class MANAGED HeapReference : public ObjectReference<kPoisonHeapReferences, MirrorType> {
     84  public:
     85   static HeapReference<MirrorType> FromMirrorPtr(MirrorType* mirror_ptr)
     86       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     87     return HeapReference<MirrorType>(mirror_ptr);
     88   }
     89  private:
     90   HeapReference<MirrorType>(MirrorType* mirror_ptr) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
     91       : ObjectReference<kPoisonHeapReferences, MirrorType>(mirror_ptr) {}
     92 };
     93 
     94 // Standard compressed reference used in the runtime. Used for StackReference and GC roots.
     95 template<class MirrorType>
     96 class MANAGED CompressedReference : public mirror::ObjectReference<false, MirrorType> {
     97  public:
     98   CompressedReference<MirrorType>() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
     99       : mirror::ObjectReference<false, MirrorType>(nullptr) {}
    100 
    101   static CompressedReference<MirrorType> FromMirrorPtr(MirrorType* p)
    102       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    103     return CompressedReference<MirrorType>(p);
    104   }
    105 
    106  private:
    107   CompressedReference<MirrorType>(MirrorType* p) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
    108       : mirror::ObjectReference<false, MirrorType>(p) {}
    109 };
    110 
    111 }  // namespace mirror
    112 }  // namespace art
    113 
    114 #endif  // ART_RUNTIME_MIRROR_OBJECT_REFERENCE_H_
    115