Use TerminateProcess to exit early (#16575)

Closes MSFT:46744208

BODGY: If the emperor is being dtor'd, it's because we've gone past the
end of main, and released the ref in main. Then we might run into an
edge case where main releases it's ref to the emperor, but one of the
window threads might be in the process of exiting, and still holding a
strong ref to the emperor. In that case, we can actually end up with
the _window thread_ being the last reference, and calling App::Close
on that thread will crash us with a E_WRONG_THREAD.

This fixes the issue by calling `TerminateProcess` explicitly.

How validated: The ES team manually ran the test pass this was
crashing in a hundred times to make sure this actually fixed it. 

Co-authored-by: Leonard Hecker <lhecker@microsoft.com>

src/cascadia/WindowsTerminal/WindowEmperor.cpp

@@ -34,26 +34,6 @@ WindowEmperor::WindowEmperor() noexcept :
     });
 
     _dispatcher = winrt::Windows::System::DispatcherQueue::GetForCurrentThread();
-
-    // BODGY
-    //
-    // There's a mysterious crash in XAML on Windows 10 if you just let the App
-    // get dtor'd. By all accounts, it doesn't make sense. To mitigate this, we
-    // need to intentionally leak a reference to our App. Crazily, if you just
-    // let the app get cleaned up with the rest of the process when the process
-    // exits, then it doesn't crash. But if you let it get explicitly dtor'd, it
-    // absolutely will crash on exit.
-    //
-    // GH#15410 has more details.
-
-    auto a{ _app };
-    ::winrt::detach_abi(a);
-}
-
-WindowEmperor::~WindowEmperor()
-{
-    _app.Close();
-    _app = nullptr;
 }
 
 void _buildArgsFromCommandline(std::vector<winrt::hstring>& args)
@@ -78,7 +58,7 @@ void _buildArgsFromCommandline(std::vector<winrt::hstring>& args)
     }
 }
 
-bool WindowEmperor::HandleCommandlineArgs(int nCmdShow)
+void WindowEmperor::HandleCommandlineArgs(int nCmdShow)
 {
     std::vector<winrt::hstring> args;
     _buildArgsFromCommandline(args);
@@ -97,13 +77,13 @@ bool WindowEmperor::HandleCommandlineArgs(int nCmdShow)
     const Remoting::CommandlineArgs eventArgs{ args, cwd, gsl::narrow_cast<uint32_t>(nCmdShow), GetEnvironmentStringsW() };
     const auto isolatedMode{ _app.Logic().IsolatedMode() };
     const auto result = _manager.ProposeCommandline(eventArgs, isolatedMode);
+    int exitCode = 0;
 
-    const bool makeWindow = result.ShouldCreateWindow();
-    if (makeWindow)
+    if (result.ShouldCreateWindow())
     {
         _createNewWindowThread(Remoting::WindowRequestedArgs{ result, eventArgs });
-
         _becomeMonarch();
+        WaitForWindows();
     }
     else
     {
@@ -111,11 +91,16 @@ bool WindowEmperor::HandleCommandlineArgs(int nCmdShow)
         if (!res.Message.empty())
         {
             AppHost::s_DisplayMessageBox(res);
-            std::quick_exit(res.ExitCode);
         }
+        exitCode = res.ExitCode;
     }
 
-    return makeWindow;
+    // There's a mysterious crash in XAML on Windows 10 if you just let _app get destroyed (GH#15410).
+    // We also need to ensure that all UI threads exit before WindowEmperor leaves the scope on the main thread (MSFT:46744208).
+    // Both problems can be solved and the shutdown accelerated by using TerminateProcess.
+    // std::exit(), etc., cannot be used here, because those use ExitProcess for unpackaged applications.
+    TerminateProcess(GetCurrentProcess(), gsl::narrow_cast<UINT>(exitCode));
+    __assume(false);
 }
 
 void WindowEmperor::WaitForWindows()
@@ -568,15 +553,6 @@ LRESULT WindowEmperor::_messageHandler(UINT const message, WPARAM const wParam,
 // we'll undoubtedly crash.
 winrt::fire_and_forget WindowEmperor::_close()
 {
-    {
-        auto fridge{ _oldThreads.lock() };
-        for (auto& window : *fridge)
-        {
-            window->ThrowAway();
-        }
-        fridge->clear();
-    }
-
     // Important! Switch back to the main thread for the emperor. That way, the
     // quit will go to the emperor's message pump.
     co_await wil::resume_foreground(_dispatcher);

src/cascadia/WindowsTerminal/WindowEmperor.h

@@ -24,10 +24,9 @@ class WindowEmperor : public std::enable_shared_from_this<WindowEmperor>
 {
 public:
     WindowEmperor() noexcept;
-    ~WindowEmperor();
     void WaitForWindows();
 
-    bool HandleCommandlineArgs(int nCmdShow);
+    void HandleCommandlineArgs(int nCmdShow);
 
 private:
     void _createNewWindowThread(const winrt::Microsoft::Terminal::Remoting::WindowRequestedArgs& args);

src/cascadia/WindowsTerminal/main.cpp

@@ -115,8 +115,5 @@ int __stdcall wWinMain(HINSTANCE, HINSTANCE, LPWSTR, int nCmdShow)
     winrt::init_apartment(winrt::apartment_type::single_threaded);
 
     const auto emperor = std::make_shared<::WindowEmperor>();
-    if (emperor->HandleCommandlineArgs(nCmdShow))
-    {
-        emperor->WaitForWindows();
-    }
+    emperor->HandleCommandlineArgs(nCmdShow);
 }