zcpointer.h

   1 // Copyright 2016 Google Inc. All rights reserved.
   2 //
   3 // Licensed under the Apache License, Version 2.0 (the "License");
   4 // you may not use this file except in compliance with the License.
   5 // You may obtain a copy of the License at
   6 //
   7 //     http://www.apache.org/licenses/LICENSE-2.0
   8 //
   9 // Unless required by applicable law or agreed to in writing, software
  10 // distributed under the License is distributed on an "AS IS" BASIS,
  11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 // See the License for the specific language governing permissions and
  13 // limitations under the License.
  14
  15 #include <limits>
  16 #include <memory>
  17 #include <forward_list>
  18
  19 namespace zc {
  20
  21 #if defined(ZCPOINTER_TRACK_REFS) && ZCPOINTER_TRACK_REFS
  22
  23 template <typename T> class ref;
  24
  25 namespace internal {
  26
  27 template <typename T>
  28 class OwnedPtrDeleter {
  29  public:
  30   OwnedPtrDeleter() {}
  31   ~OwnedPtrDeleter() {}
  32
  33   OwnedPtrDeleter(OwnedPtrDeleter&& other) : refs_(std::move(other.refs_)) {
  34   }
  35
  36   void operator()(T* t) const {
  37     for (auto& ref : refs_) {
  38       ref->MarkDeleted();
  39     }
  40     delete t;
  41   }
  42
  43  protected:
  44   friend class ref<T>;
  45
  46   void AddRef(ref<T>* ref) {
  47     refs_.push_front(ref);
  48   }
  49
  50   void RemoveRef(ref<T>* ref) {
  51     refs_.remove(ref);
  52   }
  53
  54  private:
  55   std::forward_list<ref<T>*> refs_;
  56 };
  57
  58 void RaiseUseAfterFree(const char* error) __attribute__((noreturn));
  59
  60 }  // namespace internal
  61
  62 template <typename T>
  63 class owned : public std::unique_ptr<T, internal::OwnedPtrDeleter<T>> {
  64  private:
  65   using Deleter = internal::OwnedPtrDeleter<T>;
  66
  67  public:
  68   using std::unique_ptr<T, Deleter>::unique_ptr;
  69
  70   ref<T> get() {
  71     return ref<T>(*this);
  72   }
  73
  74  private:
  75   T* get() const {
  76     return this->std::unique_ptr<T, Deleter>::get();
  77   }
  78 };
  79
  80 template <typename T>
  81 class ref {
  82  public:
  83   ref() : ptr_(DeletedSentinel()) {}
  84
  85   explicit ref(owned<T>& o) : ptr_(&o) {
  86     ptr_->get_deleter().AddRef(this);
  87   }
  88
  89   ref(const ref<T>& o) {
  90     *this = o;
  91   }
  92
  93   ref<T>& operator=(const ref<T>& o) {
  94     ptr_ = o.ptr_;
  95     if (!IsDeleted()) {
  96       ptr_->get_deleter().AddRef(this);
  97     }
  98     return *this;
  99   }
 100
 101   ~ref() {
 102     ptr_->get_deleter().RemoveRef(this);
 103     MarkDeleted();
 104   }
 105
 106   T* operator->() const {
 107     CheckDeleted();
 108     return ptr_->operator->();
 109   }
 110
 111  protected:
 112   friend class internal::OwnedPtrDeleter<T>;
 113
 114   void MarkDeleted() {
 115     ptr_ = DeletedSentinel();
 116   }
 117
 118  private:
 119   void CheckDeleted() const {
 120     if (IsDeleted()) {
 121       internal::RaiseUseAfterFree("attempt to access deleted pointer");
 122     }
 123   }
 124
 125   bool IsDeleted() const {
 126     return ptr_ == DeletedSentinel();
 127   }
 128
 129   inline static owned<T>* DeletedSentinel() {
 130     return reinterpret_cast<owned<T>*>(std::numeric_limits<uintptr_t>::max());
 131   }
 132
 133   owned<T>* ptr_;
 134 };
 135
 136 #else
 137
 138 template <typename T>
 139 using owned = std::unique_ptr<T>;
 140
 141 template <typename T>
 142 using ref = T*;
 143
 144 #endif
 145
 146 }  // namespace zc