1 files changed, 83 insertions, 0 deletions
diff --git a/ipc/mscom/Aggregation.h b/ipc/mscom/Aggregation.h
new file mode 100644
index 0000000000..ca171e39cc
--- /dev/null
+++ b/ipc/mscom/Aggregation.h
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_mscom_Aggregation_h
+#define mozilla_mscom_Aggregation_h
+
+#include "mozilla/Attributes.h"
+
+#include <stddef.h>
+#include <unknwn.h>
+
+namespace mozilla {
+namespace mscom {
+
+/**
+ * This is used for stabilizing a COM object's reference count during
+ * construction when that object aggregates other objects. Since the aggregated
+ * object(s) may AddRef() or Release(), we need to artifically boost the
+ * refcount to prevent premature destruction. Note that we increment/decrement
+ * instead of AddRef()/Release() in this class because we want to adjust the
+ * refcount without causing any other side effects (like object destruction).
+ */
+template <typename RefCntT>
+class MOZ_RAII StabilizedRefCount {
+ public:
+  explicit StabilizedRefCount(RefCntT& aRefCnt) : mRefCnt(aRefCnt) {
+    ++aRefCnt;
+  }
+
+  ~StabilizedRefCount() { --mRefCnt; }
+
+  StabilizedRefCount(const StabilizedRefCount&) = delete;
+  StabilizedRefCount(StabilizedRefCount&&) = delete;
+  StabilizedRefCount& operator=(const StabilizedRefCount&) = delete;
+  StabilizedRefCount& operator=(StabilizedRefCount&&) = delete;
+
+ private:
+  RefCntT& mRefCnt;
+};
+
+namespace detail {
+
+template <typename T>
+class InternalUnknown : public IUnknown {
+ public:
+  STDMETHODIMP QueryInterface(REFIID aIid, void** aOutInterface) override {
+    return This()->InternalQueryInterface(aIid, aOutInterface);
+  }
+
+  STDMETHODIMP_(ULONG) AddRef() override { return This()->InternalAddRef(); }
+
+  STDMETHODIMP_(ULONG) Release() override { return This()->InternalRelease(); }
+
+ private:
+  T* This() {
+    return reinterpret_cast<T*>(reinterpret_cast<char*>(this) -
+                                offsetof(T, mInternalUnknown));
+  }
+};
+
+}  // namespace detail
+}  // namespace mscom
+}  // namespace mozilla
+
+#define DECLARE_AGGREGATABLE(Type)                                      \
+ public:                                                                \
+  STDMETHODIMP QueryInterface(REFIID riid, void** ppv) override {       \
+    return mOuter->QueryInterface(riid, ppv);                           \
+  }                                                                     \
+  STDMETHODIMP_(ULONG) AddRef() override { return mOuter->AddRef(); }   \
+  STDMETHODIMP_(ULONG) Release() override { return mOuter->Release(); } \
+                                                                        \
+ protected:                                                             \
+  STDMETHODIMP InternalQueryInterface(REFIID riid, void** ppv);         \
+  STDMETHODIMP_(ULONG) InternalAddRef();                                \
+  STDMETHODIMP_(ULONG) InternalRelease();                               \
+  friend class mozilla::mscom::detail::InternalUnknown<Type>;           \
+  mozilla::mscom::detail::InternalUnknown<Type> mInternalUnknown
+
+#endif  // mozilla_mscom_Aggregation_h