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:
StabilizedRefCount(RefCntT & aRefCnt)29   explicit StabilizedRefCount(RefCntT& aRefCnt) : mRefCnt(aRefCnt) {
30     ++aRefCnt;
31   }
32 
~StabilizedRefCount()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:
QueryInterface(REFIID aIid,void ** aOutInterface)49   STDMETHODIMP QueryInterface(REFIID aIid, void** aOutInterface) override {
50     return This()->InternalQueryInterface(aIid, aOutInterface);
51   }
52 
AddRef()53   STDMETHODIMP_(ULONG) AddRef() override { return This()->InternalAddRef(); }
54 
Release()55   STDMETHODIMP_(ULONG) Release() override { return This()->InternalRelease(); }
56 
57  private:
This()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
84