ipc/mscom/Aggregation.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_mscom_Aggregation_h
   8 #define mozilla_mscom_Aggregation_h
   9
  10 #include "mozilla/Attributes.h"
  11
  12 #include <stddef.h>
  13 #include <unknwn.h>
  14
  15 namespace mozilla {
  16 namespace mscom {
  17
  18 /**
  19  * This is used for stabilizing a COM object's reference count during
  20  * construction when that object aggregates other objects. Since the aggregated
  21  * object(s) may AddRef() or Release(), we need to artifically boost the
  22  * refcount to prevent premature destruction. Note that we increment/decrement
  23  * instead of AddRef()/Release() in this class because we want to adjust the
  24  * refcount without causing any other side effects (like object destruction).
  25  */
  26 template <typename RefCntT>
  27 class MOZ_RAII StabilizedRefCount {
  28  public:
  29   explicit StabilizedRefCount(RefCntT& aRefCnt) : mRefCnt(aRefCnt) {
  30     ++aRefCnt;
  31   }
  32
  33   ~StabilizedRefCount() { --mRefCnt; }
  34
  35   StabilizedRefCount(const StabilizedRefCount&) = delete;
  36   StabilizedRefCount(StabilizedRefCount&&) = delete;
  37   StabilizedRefCount& operator=(const StabilizedRefCount&) = delete;
  38   StabilizedRefCount& operator=(StabilizedRefCount&&) = delete;
  39
  40  private:
  41   RefCntT& mRefCnt;
  42 };
  43
  44 namespace detail {
  45
  46 template <typename T>
  47 class InternalUnknown : public IUnknown {
  48  public:
  49   STDMETHODIMP QueryInterface(REFIID aIid, void** aOutInterface) override {
  50     return This()->InternalQueryInterface(aIid, aOutInterface);
  51   }
  52
  53   STDMETHODIMP_(ULONG) AddRef() override { return This()->InternalAddRef(); }
  54
  55   STDMETHODIMP_(ULONG) Release() override { return This()->InternalRelease(); }
  56
  57  private:
  58   T* This() {
  59     return reinterpret_cast<T*>(reinterpret_cast<char*>(this) -
  60                                 offsetof(T, mInternalUnknown));
  61   }
  62 };
  63
  64 }  // namespace detail
  65 }  // namespace mscom
  66 }  // namespace mozilla
  67
  68 #define DECLARE_AGGREGATABLE(Type)                                      \
  69  public:                                                                \
  70   STDMETHODIMP QueryInterface(REFIID riid, void** ppv) override {       \
  71     return mOuter->QueryInterface(riid, ppv);                           \
  72   }                                                                     \
  73   STDMETHODIMP_(ULONG) AddRef() override { return mOuter->AddRef(); }   \
  74   STDMETHODIMP_(ULONG) Release() override { return mOuter->Release(); } \
  75                                                                         \
  76  protected:                                                             \
  77   STDMETHODIMP InternalQueryInterface(REFIID riid, void** ppv);         \
  78   STDMETHODIMP_(ULONG) InternalAddRef();                                \
  79   STDMETHODIMP_(ULONG) InternalRelease();                               \
  80   friend class mozilla::mscom::detail::InternalUnknown<Type>;           \
  81   mozilla::mscom::detail::InternalUnknown<Type> mInternalUnknown
  82
  83 #endif  // mozilla_mscom_Aggregation_h