1 files changed, 137 insertions, 0 deletions
diff --git a/mozglue/misc/DynamicallyLinkedFunctionPtr.h b/mozglue/misc/DynamicallyLinkedFunctionPtr.h
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+++ b/mozglue/misc/DynamicallyLinkedFunctionPtr.h
@@ -0,0 +1,137 @@
+/* -*- 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_DynamicallyLinkedFunctionPtr_h
+#define mozilla_DynamicallyLinkedFunctionPtr_h
+
+#include <windows.h>
+
+#include <utility>
+
+#include "mozilla/Attributes.h"
+
+namespace mozilla {
+namespace detail {
+
+template <typename T>
+struct FunctionPtrCracker;
+
+template <typename R, typename... Args>
+struct FunctionPtrCracker<R (*)(Args...)> {
+  using ReturnT = R;
+  using FunctionPtrT = R (*)(Args...);
+};
+
+#if defined(_M_IX86)
+template <typename R, typename... Args>
+struct FunctionPtrCracker<R(__stdcall*)(Args...)> {
+  using ReturnT = R;
+  using FunctionPtrT = R(__stdcall*)(Args...);
+};
+
+template <typename R, typename... Args>
+struct FunctionPtrCracker<R(__fastcall*)(Args...)> {
+  using ReturnT = R;
+  using FunctionPtrT = R(__fastcall*)(Args...);
+};
+#endif  // defined(_M_IX86)
+
+template <typename T>
+class DynamicallyLinkedFunctionPtrBase {
+ public:
+  using ReturnT = typename FunctionPtrCracker<T>::ReturnT;
+  using FunctionPtrT = typename FunctionPtrCracker<T>::FunctionPtrT;
+
+  DynamicallyLinkedFunctionPtrBase(const wchar_t* aLibName,
+                                   const char* aFuncName)
+      : mModule(::LoadLibraryW(aLibName)), mFunction(nullptr) {
+    if (!mModule) {
+      return;
+    }
+
+    mFunction =
+        reinterpret_cast<FunctionPtrT>(::GetProcAddress(mModule, aFuncName));
+
+    if (!mFunction) {
+      // Since the function doesn't exist, there is no point in holding a
+      // reference to mModule anymore.
+      ::FreeLibrary(mModule);
+      mModule = nullptr;
+    }
+  }
+
+  DynamicallyLinkedFunctionPtrBase(const DynamicallyLinkedFunctionPtrBase&) =
+      delete;
+  DynamicallyLinkedFunctionPtrBase& operator=(
+      const DynamicallyLinkedFunctionPtrBase&) = delete;
+
+  DynamicallyLinkedFunctionPtrBase(DynamicallyLinkedFunctionPtrBase&&) = delete;
+  DynamicallyLinkedFunctionPtrBase& operator=(
+      DynamicallyLinkedFunctionPtrBase&&) = delete;
+
+  template <typename... Args>
+  ReturnT operator()(Args&&... args) const {
+    return mFunction(std::forward<Args>(args)...);
+  }
+
+  explicit operator bool() const { return !!mFunction; }
+
+ protected:
+  HMODULE mModule;
+  FunctionPtrT mFunction;
+};
+
+}  // namespace detail
+
+/**
+ * In most cases, this class is the one that you want to use for resolving a
+ * dynamically-linked function pointer. It should be instantiated as a static
+ * local variable.
+ *
+ * NB: It has a trivial destructor, so the DLL that is loaded is never freed.
+ * Assuming that this function is called fairly often, this is the most
+ * sensible option. OTOH, if the function you are calling is a one-off, or the
+ * static local requirement is too restrictive, use DynamicallyLinkedFunctionPtr
+ * instead.
+ */
+template <typename T>
+class MOZ_STATIC_LOCAL_CLASS StaticDynamicallyLinkedFunctionPtr final
+    : public detail::DynamicallyLinkedFunctionPtrBase<T> {
+ public:
+  StaticDynamicallyLinkedFunctionPtr(const wchar_t* aLibName,
+                                     const char* aFuncName)
+      : detail::DynamicallyLinkedFunctionPtrBase<T>(aLibName, aFuncName) {}
+
+  /**
+   * We only offer this operator for the static local case, as it is not
+   * possible for this object to be destroyed while the returned pointer is
+   * being held.
+   */
+  operator typename detail::DynamicallyLinkedFunctionPtrBase<T>::FunctionPtrT()
+      const {
+    return this->mFunction;
+  }
+};
+
+template <typename T>
+class MOZ_NON_PARAM MOZ_NON_TEMPORARY_CLASS DynamicallyLinkedFunctionPtr final
+    : public detail::DynamicallyLinkedFunctionPtrBase<T> {
+ public:
+  DynamicallyLinkedFunctionPtr(const wchar_t* aLibName, const char* aFuncName)
+      : detail::DynamicallyLinkedFunctionPtrBase<T>(aLibName, aFuncName) {}
+
+  ~DynamicallyLinkedFunctionPtr() {
+    if (!this->mModule) {
+      return;
+    }
+
+    ::FreeLibrary(this->mModule);
+  }
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_DynamicallyLinkedFunctionPtr_h