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