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two-phase initialization support to prevent double-destruction on handing out this pointer in ctor (#1130)
* two-phase initialization support to prevent double-destruction on handing out this pointer in ctor * PR feedback - primarily to hide/downplay the need to support Xaml with two-phase init * should Release on exception * remove unnecessary test case * PR feedback * use smart pointer instead of raw delete
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-27
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13 files changed

+202
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‎cppwinrt/component_writers.h‎

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@@ -860,7 +860,9 @@ catch (...) { return winrt::to_hresult(); }
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{
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auto format = R"(
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#if defined(WINRT_FORCE_INCLUDE_%_XAML_G_H) || __has_include("%.xaml.g.h")
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#include "%.xaml.g.h"
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#else
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namespace winrt::@::implementation

‎nuget/readme.md‎

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@@ -77,6 +77,41 @@ To customize common C++/WinRT project properties:
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* expand the Common Properties item
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* select the C++/WinRT property page
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## InitializeComponent
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In older versions of C++/WinRT, Xaml objects called InitializeComponent from constructors. This can lead to memory corruption if InitializeComponent throws an exception.
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```cpp
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void MainPage::MainPage()
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{
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// This pattern should no longer be used
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InitializeComponent();
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}
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```
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C++/WinRT now calls InitializeComponent automatically and safely, after object construction. Explicit calls to InitializeComponent from constructors in existing code should now be removed. Multiple calls to InitializeComponent are idempotent.
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If a Xaml object needs to access a Xaml property during initialization, it should override InitializeComponent:
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```cpp
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void MainPage::InitializeComponent()
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{
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// Call base InitializeComponent() to register with the Xaml runtime
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MainPageT::InitializeComponent();
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// Can now access Xaml properties
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MyButton().Content(box_value(L"Click"));
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}
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```
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A non-Xaml object can also participate in two-phase construction by defining an InitializeComponent method.
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```cpp
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void MyComponent::InitializeComponent()
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{
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// Execute initialization logic that may throw
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}
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```
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## Troubleshooting
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The msbuild verbosity level maps to msbuild message importance as follows:

‎strings/base_implements.h‎

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@@ -1218,6 +1218,29 @@ namespace winrt::impl
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};
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#endif
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template<typename T>
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class has_initializer
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{
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template <typename U, typename = decltype(std::declval<U>().InitializeComponent())> static constexpr bool get_value(int) { return true; }
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template <typename> static constexpr bool get_value(...) { return false; }
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public:
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static constexpr bool value = get_value<T>(0);
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};
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template<typename T, typename... Args>
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T* create_and_initialize(Args&&... args)
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{
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com_ptr<T> instance{ new heap_implements<T>(std::forward<Args>(args)...), take_ownership_from_abi };
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if constexpr (has_initializer<T>::value)
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{
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instance->InitializeComponent();
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}
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return instance.detach();
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}
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inline com_ptr<IStaticLifetimeCollection> get_static_lifetime_map()
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{
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auto const lifetime_factory = get_activation_factory<impl::IStaticLifetime>(L"Windows.ApplicationModel.Core.CoreApplication");
@@ -1233,7 +1256,7 @@ namespace winrt::impl
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if constexpr (!has_static_lifetime_v<D>)
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{
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return { to_abi<result_type>(new heap_implements<D>), take_ownership_from_abi };
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return { to_abi<result_type>(create_and_initialize<D>()), take_ownership_from_abi };
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}
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else
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{
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return { result, take_ownership_from_abi };
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}
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result_type object{ to_abi<result_type>(new heap_implements<D>), take_ownership_from_abi };
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result_type object{ to_abi<result_type>(create_and_initialize<D>()), take_ownership_from_abi };
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static slim_mutex lock;
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slim_lock_guard const guard{ lock };
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}
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else if constexpr (impl::has_composable<D>::value)
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{
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impl::com_ref<I> result{ to_abi<I>(new impl::heap_implements<D>(std::forward<Args>(args)...)), take_ownership_from_abi };
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impl::com_ref<I> result{ to_abi<I>(impl::create_and_initialize<D>(std::forward<Args>(args)...)), take_ownership_from_abi };
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return result.template as<typename D::composable>();
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}
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else if constexpr (impl::has_class_type<D>::value)
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{
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static_assert(std::is_same_v<I, default_interface<typename D::class_type>>);
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return typename D::class_type{ to_abi<I>(new impl::heap_implements<D>(std::forward<Args>(args)...)), take_ownership_from_abi };
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return typename D::class_type{ to_abi<I>(impl::create_and_initialize<D>(std::forward<Args>(args)...)), take_ownership_from_abi };
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}
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else
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{
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return impl::com_ref<I>{ to_abi<I>(new impl::heap_implements<D>(std::forward<Args>(args)...)), take_ownership_from_abi };
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return impl::com_ref<I>{ to_abi<I>(impl::create_and_initialize<D>(std::forward<Args>(args)...)), take_ownership_from_abi };
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}
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}
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@@ -1325,7 +1348,7 @@ WINRT_EXPORT namespace winrt
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}
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else
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{
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return { new impl::heap_implements<D>(std::forward<Args>(args)...), take_ownership_from_abi };
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return { impl::create_and_initialize<D>(std::forward<Args>(args)...), take_ownership_from_abi };
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}
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}
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‎test/test/initialize.cpp‎

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@@ -0,0 +1,119 @@
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#include "pch.h"
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using namespace winrt;
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using namespace Windows::Foundation;
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namespace
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{
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class some_exception : public std::exception
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{
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public:
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some_exception() noexcept
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: exception("some_exception", 1)
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{
14+
}
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};
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template<typename D>
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struct InitializeT : implements<D, IStringable>
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{
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bool& m_initialize_called;
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InitializeT(bool& initialize_called) : m_initialize_called(initialize_called)
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{
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}
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~InitializeT()
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{
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}
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void InitializeComponent()
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{
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m_initialize_called = true;
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throw some_exception();
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}
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hstring ToString()
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{
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return {};
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}
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};
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struct Initialize : InitializeT<Initialize>
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{
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Initialize(bool& initialize_called) : InitializeT(initialize_called)
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{
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}
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};
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struct ThrowingDerived : InitializeT<ThrowingDerived>
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{
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ThrowingDerived(bool& initialize_called) : InitializeT(initialize_called)
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{
53+
throw some_exception();
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}
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};
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struct OverriddenInitialize : InitializeT<OverriddenInitialize>
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{
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OverriddenInitialize(bool& initialize_called) : InitializeT(initialize_called)
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{
61+
}
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void InitializeComponent()
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{
65+
m_initialize_called = true;
66+
}
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};
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}
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TEST_CASE("initialize")
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{
72+
// Ensure that failure to initialize is failure to instantiate, with no side effects
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{
74+
bool initialize_called{};
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bool exception_caught{};
76+
try
77+
{
78+
make<Initialize>(initialize_called);
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}
80+
catch (some_exception const&)
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{
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exception_caught = true;
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}
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REQUIRE(initialize_called);
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REQUIRE(exception_caught);
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}
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// Ensure that base is never initialized if exception thrown from derived/base constructor
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{
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bool initialize_called{};
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bool exception_caught{};
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try
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{
94+
make<ThrowingDerived>(initialize_called);
95+
}
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catch (some_exception const&)
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{
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exception_caught = true;
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}
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REQUIRE(!initialize_called);
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REQUIRE(exception_caught);
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}
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// Support for overriding initialization for post-processing (e.g., accessing Xaml properties)
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{
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bool initialize_called{};
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bool exception_caught{};
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try
109+
{
110+
make<OverriddenInitialize>(initialize_called);
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}
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catch (some_exception const&)
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{
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exception_caught = true;
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}
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REQUIRE(initialize_called);
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REQUIRE(!exception_caught);
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}
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}

‎test/test/test.vcxproj‎

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</ClCompile>
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<ClCompile Include="hstring_empty.cpp" />
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<ClCompile Include="iid_ppv_args.cpp" />
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<ClCompile Include="initialize.cpp" />
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<ClCompile Include="inspectable_interop.cpp">
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<PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">NotUsing</PrecompiledHeader>
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<PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">NotUsing</PrecompiledHeader>

‎vsix/ItemTemplates/BlankPage/BlankPage.cpp‎

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@@ -9,11 +9,6 @@ using namespace Windows::UI::Xaml;
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namespace winrt::$rootnamespace$::implementation
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{
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$safeitemname$::$safeitemname$()
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{
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InitializeComponent();
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}
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int32_t $safeitemname$::MyProperty()
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{
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throw hresult_not_implemented();

‎vsix/ItemTemplates/BlankPage/BlankPage.h‎

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@@ -6,7 +6,11 @@ namespace winrt::$rootnamespace$::implementation
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{
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struct $safeitemname$ : $safeitemname$T<$safeitemname$>
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{
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$safeitemname$();
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$safeitemname$()
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{
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// Xaml objects should not call InitializeComponent during construction.
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// See https://github.com/microsoft/cppwinrt/tree/master/nuget#initializecomponent
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}
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int32_t MyProperty();
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void MyProperty(int32_t value);

‎vsix/ItemTemplates/BlankUserControl/BlankUserControl.cpp‎

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namespace winrt::$rootnamespace$::implementation
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{
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$safeitemname$::$safeitemname$()
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{
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InitializeComponent();
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}
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int32_t $safeitemname$::MyProperty()
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{
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throw hresult_not_implemented();

‎vsix/ItemTemplates/BlankUserControl/BlankUserControl.h‎

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@@ -10,7 +10,11 @@ namespace winrt::$rootnamespace$::implementation
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{
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struct $safeitemname$ : $safeitemname$T<$safeitemname$>
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{
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$safeitemname$();
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$safeitemname$()
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{
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// Xaml objects should not call InitializeComponent during construction.
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// See https://github.com/microsoft/cppwinrt/tree/master/nuget#initializecomponent
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}
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int32_t MyProperty();
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void MyProperty(int32_t value);

‎vsix/ProjectTemplates/VC/Windows Universal/BlankApp/App.cpp‎

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@@ -14,12 +14,11 @@ using namespace $safeprojectname$;
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using namespace $safeprojectname$::implementation;
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/// <summary>
17-
/// Initializes the singleton application object. This is the first line of authored code
17+
/// Creates the singleton application object. This is the first line of authored code
1818
/// executed, and as such is the logical equivalent of main() or WinMain().
1919
/// </summary>
2020
App::App()
2121
{
22-
InitializeComponent();
2322
Suspending({ this, &App::OnSuspending });
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2524
#if defined _DEBUG && !defined DISABLE_XAML_GENERATED_BREAK_ON_UNHANDLED_EXCEPTION

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