mojo/public/cpp/bindings/lib/shared_data.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_SHARED_DATA_H_
   6 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_SHARED_DATA_H_
   7
   8 #include "mojo/public/cpp/system/macros.h"
   9
  10 namespace mojo {
  11 namespace internal {
  12
  13 // Used to allocate an instance of T that can be shared via reference counting.
  14 template <typename T>
  15 class SharedData {
  16  public:
  17   ~SharedData() {
  18     holder_->Release();
  19   }
  20
  21   SharedData() : holder_(new Holder()) {
  22   }
  23
  24   explicit SharedData(const T& value) : holder_(new Holder(value)) {
  25   }
  26
  27   SharedData(const SharedData<T>& other) : holder_(other.holder_) {
  28     holder_->Retain();
  29   }
  30
  31   SharedData<T>& operator=(const SharedData<T>& other) {
  32     if (other.holder_ == holder_)
  33       return *this;
  34     holder_->Release();
  35     holder_ = other.holder_;
  36     holder_->Retain();
  37     return *this;
  38   }
  39
  40   void reset() {
  41     holder_->Release();
  42     holder_ = new Holder();
  43   }
  44
  45   void reset(const T& value) {
  46     holder_->Release();
  47     holder_ = new Holder(value);
  48   }
  49
  50   void set_value(const T& value) {
  51     holder_->value = value;
  52   }
  53   T* mutable_value() {
  54     return &holder_->value;
  55   }
  56   const T& value() const {
  57     return holder_->value;
  58   }
  59
  60  private:
  61   class Holder {
  62    public:
  63     Holder() : value(), ref_count_(1) {
  64     }
  65     Holder(const T& value) : value(value), ref_count_(1) {
  66     }
  67
  68     void Retain() { ++ref_count_; }
  69     void Release() { if (--ref_count_ == 0) delete this; }
  70
  71     T value;
  72
  73    private:
  74     int ref_count_;
  75     MOJO_DISALLOW_COPY_AND_ASSIGN(Holder);
  76   };
  77
  78   Holder* holder_;
  79 };
  80
  81 }  // namespace internal
  82 }  // namespace mojo
  83
  84 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SHARED_DATA_H_