1 files changed, 142 insertions, 0 deletions
diff --git a/ipc/mscom/WeakRef.h b/ipc/mscom/WeakRef.h
new file mode 100644
index 0000000000..ba87eecb70
--- /dev/null
+++ b/ipc/mscom/WeakRef.h
@@ -0,0 +1,142 @@
+/* -*- 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_WeakRef_h
+#define mozilla_mscom_WeakRef_h
+
+#include <guiddef.h>
+#include <unknwn.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/RefPtr.h"
+#include "nsISupportsImpl.h"
+
+/**
+ * Thread-safe weak references for COM that works pre-Windows 8 and do not
+ * require WinRT.
+ */
+
+namespace mozilla {
+namespace mscom {
+
+struct IWeakReferenceSource;
+class WeakReferenceSupport;
+
+namespace detail {
+
+class SharedRef final {
+ public:
+  explicit SharedRef(WeakReferenceSupport* aSupport);
+  void Lock();
+  void Unlock();
+
+  HRESULT ToStrongRef(IWeakReferenceSource** aOutStringReference);
+  HRESULT Resolve(REFIID aIid, void** aOutStrongReference);
+  void Clear();
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedRef)
+
+  SharedRef(const SharedRef&) = delete;
+  SharedRef(SharedRef&&) = delete;
+  SharedRef& operator=(const SharedRef&) = delete;
+  SharedRef& operator=(SharedRef&&) = delete;
+
+ private:
+  ~SharedRef();
+
+ private:
+  CRITICAL_SECTION mCS;
+  WeakReferenceSupport* mSupport;
+};
+
+}  // namespace detail
+
+// {F841AEFA-064C-49A4-B73D-EBD14A90F012}
+DEFINE_GUID(IID_IWeakReference, 0xf841aefa, 0x64c, 0x49a4, 0xb7, 0x3d, 0xeb,
+            0xd1, 0x4a, 0x90, 0xf0, 0x12);
+
+struct IWeakReference : public IUnknown {
+  virtual STDMETHODIMP ToStrongRef(
+      IWeakReferenceSource** aOutStrongReference) = 0;
+  virtual STDMETHODIMP Resolve(REFIID aIid, void** aOutStrongReference) = 0;
+};
+
+// {87611F0C-9BBB-4F78-9D43-CAC5AD432CA1}
+DEFINE_GUID(IID_IWeakReferenceSource, 0x87611f0c, 0x9bbb, 0x4f78, 0x9d, 0x43,
+            0xca, 0xc5, 0xad, 0x43, 0x2c, 0xa1);
+
+struct IWeakReferenceSource : public IUnknown {
+  virtual STDMETHODIMP GetWeakReference(IWeakReference** aOutWeakRef) = 0;
+};
+
+class WeakRef;
+
+class WeakReferenceSupport : public IWeakReferenceSource {
+ public:
+  enum class Flags { eNone = 0, eDestroyOnMainThread = 1 };
+
+  // IUnknown
+  STDMETHODIMP QueryInterface(REFIID riid, void** ppv) override;
+  STDMETHODIMP_(ULONG) AddRef() override;
+  STDMETHODIMP_(ULONG) Release() override;
+
+  // IWeakReferenceSource
+  STDMETHODIMP GetWeakReference(IWeakReference** aOutWeakRef) override;
+
+ protected:
+  explicit WeakReferenceSupport(Flags aFlags);
+  virtual ~WeakReferenceSupport() = default;
+
+  virtual HRESULT WeakRefQueryInterface(REFIID aIid,
+                                        IUnknown** aOutInterface) = 0;
+
+  class MOZ_RAII StabilizeRefCount final {
+   public:
+    explicit StabilizeRefCount(WeakReferenceSupport& aObject);
+    ~StabilizeRefCount();
+
+    StabilizeRefCount(const StabilizeRefCount&) = delete;
+    StabilizeRefCount(StabilizeRefCount&&) = delete;
+    StabilizeRefCount& operator=(const StabilizeRefCount&) = delete;
+    StabilizeRefCount& operator=(StabilizeRefCount&&) = delete;
+
+   private:
+    WeakReferenceSupport& mObject;
+  };
+
+  friend class StabilizeRefCount;
+
+ private:
+  RefPtr<detail::SharedRef> mSharedRef;
+  ULONG mRefCnt;
+  Flags mFlags;
+};
+
+class WeakRef final : public IWeakReference {
+ public:
+  // IUnknown
+  STDMETHODIMP QueryInterface(REFIID riid, void** ppv) override;
+  STDMETHODIMP_(ULONG) AddRef() override;
+  STDMETHODIMP_(ULONG) Release() override;
+
+  // IWeakReference
+  STDMETHODIMP ToStrongRef(IWeakReferenceSource** aOutStrongReference) override;
+  STDMETHODIMP Resolve(REFIID aIid, void** aOutStrongReference) override;
+
+  explicit WeakRef(RefPtr<detail::SharedRef>& aSharedRef);
+
+ private:
+  ~WeakRef() = default;
+
+  Atomic<ULONG> mRefCnt;
+  RefPtr<detail::SharedRef> mSharedRef;
+};
+
+}  // namespace mscom
+}  // namespace mozilla
+
+#endif  // mozilla_mscom_WeakRef_h