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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_HANDLE_H_
     18 #define ART_RUNTIME_HANDLE_H_
     19 
     20 #include "base/casts.h"
     21 #include "base/logging.h"
     22 #include "base/macros.h"
     23 #include "base/value_object.h"
     24 #include "stack.h"
     25 
     26 namespace art {
     27 
     28 class Thread;
     29 
     30 template<class T> class Handle;
     31 
     32 // Handles are memory locations that contain GC roots. As the mirror::Object*s within a handle are
     33 // GC visible then the GC may move the references within them, something that couldn't be done with
     34 // a wrap pointer. Handles are generally allocated within HandleScopes. Handle is a super-class
     35 // of MutableHandle and doesn't support assignment operations.
     36 template<class T>
     37 class Handle : public ValueObject {
     38  public:
     39   Handle() : reference_(nullptr) {
     40   }
     41 
     42   ALWAYS_INLINE Handle(const Handle<T>& handle) : reference_(handle.reference_) {
     43   }
     44 
     45   ALWAYS_INLINE Handle<T>& operator=(const Handle<T>& handle) {
     46     reference_ = handle.reference_;
     47     return *this;
     48   }
     49 
     50   ALWAYS_INLINE explicit Handle(StackReference<T>* reference) : reference_(reference) {
     51   }
     52 
     53   ALWAYS_INLINE T& operator*() const SHARED_REQUIRES(Locks::mutator_lock_) {
     54     return *Get();
     55   }
     56 
     57   ALWAYS_INLINE T* operator->() const SHARED_REQUIRES(Locks::mutator_lock_) {
     58     return Get();
     59   }
     60 
     61   ALWAYS_INLINE T* Get() const SHARED_REQUIRES(Locks::mutator_lock_) {
     62     return down_cast<T*>(reference_->AsMirrorPtr());
     63   }
     64 
     65   ALWAYS_INLINE jobject ToJObject() const SHARED_REQUIRES(Locks::mutator_lock_) {
     66     if (UNLIKELY(reference_->AsMirrorPtr() == nullptr)) {
     67       // Special case so that we work with null handles.
     68       return nullptr;
     69     }
     70     return reinterpret_cast<jobject>(reference_);
     71   }
     72 
     73   ALWAYS_INLINE StackReference<mirror::Object>* GetReference() {
     74     return reference_;
     75   }
     76 
     77   ALWAYS_INLINE const StackReference<mirror::Object>* GetReference() const {
     78     return reference_;
     79   }
     80 
     81  protected:
     82   template<typename S>
     83   explicit Handle(StackReference<S>* reference)
     84       : reference_(reference) {
     85   }
     86   template<typename S>
     87   explicit Handle(const Handle<S>& handle)
     88       : reference_(handle.reference_) {
     89   }
     90 
     91   StackReference<mirror::Object>* reference_;
     92 
     93  private:
     94   friend class BuildGenericJniFrameVisitor;
     95   template<class S> friend class Handle;
     96   friend class HandleScope;
     97   template<class S> friend class HandleWrapper;
     98   template<size_t kNumReferences> friend class StackHandleScope;
     99 };
    100 
    101 // Handles that support assignment.
    102 template<class T>
    103 class MutableHandle : public Handle<T> {
    104  public:
    105   MutableHandle() {
    106   }
    107 
    108   ALWAYS_INLINE MutableHandle(const MutableHandle<T>& handle)
    109       SHARED_REQUIRES(Locks::mutator_lock_)
    110       : Handle<T>(handle.reference_) {
    111   }
    112 
    113   ALWAYS_INLINE MutableHandle<T>& operator=(const MutableHandle<T>& handle)
    114       SHARED_REQUIRES(Locks::mutator_lock_) {
    115     Handle<T>::operator=(handle);
    116     return *this;
    117   }
    118 
    119   ALWAYS_INLINE explicit MutableHandle(StackReference<T>* reference)
    120       SHARED_REQUIRES(Locks::mutator_lock_)
    121       : Handle<T>(reference) {
    122   }
    123 
    124   ALWAYS_INLINE T* Assign(T* reference) SHARED_REQUIRES(Locks::mutator_lock_) {
    125     StackReference<mirror::Object>* ref = Handle<T>::GetReference();
    126     T* old = down_cast<T*>(ref->AsMirrorPtr());
    127     ref->Assign(reference);
    128     return old;
    129   }
    130 
    131   template<typename S>
    132   explicit MutableHandle(const MutableHandle<S>& handle) SHARED_REQUIRES(Locks::mutator_lock_)
    133       : Handle<T>(handle) {
    134   }
    135 
    136   template<typename S>
    137   explicit MutableHandle(StackReference<S>* reference) SHARED_REQUIRES(Locks::mutator_lock_)
    138       : Handle<T>(reference) {
    139   }
    140 
    141  private:
    142   friend class BuildGenericJniFrameVisitor;
    143   friend class HandleScope;
    144   template<class S> friend class HandleWrapper;
    145   template<size_t kNumReferences> friend class StackHandleScope;
    146 };
    147 
    148 // A special case of Handle that only holds references to null. Invalid when if it goes out of
    149 // scope. Example: Handle<T> h = ScopedNullHandle<T> will leave h being undefined.
    150 template<class T>
    151 class ScopedNullHandle : public Handle<T> {
    152  public:
    153   ScopedNullHandle() : Handle<T>(&null_ref_) {}
    154 
    155  private:
    156   StackReference<mirror::Object> null_ref_;
    157 };
    158 
    159 }  // namespace art
    160 
    161 #endif  // ART_RUNTIME_HANDLE_H_
    162