Pump the message queue on frozen windows

.github/actions/spelling/expect/expect.txt

@@ -481,6 +481,7 @@ directio
 DIRECTX
 DISABLEDELAYEDEXPANSION
 DISABLENOSCROLL
+DISPATCHNOTIFY
 DISPLAYATTRIBUTE
 DISPLAYATTRIBUTEPROPERTY
 DISPLAYCHANGE

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -535,23 +535,19 @@ void AppHost::LastTabClosed(const winrt::Windows::Foundation::IInspectable& /*se
     {
         _windowLogic.ClearPersistedWindowState();
     }
-
-    // If the user closes the last tab, in the last window, _by closing the tab_
-    // (not by closing the whole window), we need to manually persist an empty
-    // window state here. That will cause the terminal to re-open with the usual
-    // settings (not the persisted state)
-    if (args.ClearPersistedState() &&
-        _windowManager.GetNumberOfPeasants() == 1)
-    {
-        _windowLogic.ClearPersistedWindowState();
-    }
-
     // Remove ourself from the list of peasants so that we aren't included in
     // any future requests. This will also mean we block until any existing
     // event handler finishes.
     _windowManager.SignalClose(_peasant);
 
-    PostQuitMessage(0);
+    if (Utils::IsWindows11())
+    {
+        PostQuitMessage(0);
+    }
+    else
+    {
+        PostMessageW(_window->GetInteropHandle(), WM_REFRIGERATE, 0, 0);
+    }
 }
 
 LaunchPosition AppHost::_GetWindowLaunchPosition()

src/cascadia/WindowsTerminal/AppHost.h

@@ -11,6 +11,8 @@
 class AppHost : public std::enable_shared_from_this<AppHost>
 {
 public:
+    static constexpr DWORD WM_REFRIGERATE = WM_APP + 0;
+
     AppHost(const winrt::TerminalApp::AppLogic& logic,
             winrt::Microsoft::Terminal::Remoting::WindowRequestedArgs args,
             const winrt::Microsoft::Terminal::Remoting::WindowManager& manager,

src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp

@@ -26,6 +26,11 @@ NonClientIslandWindow::NonClientIslandWindow(const ElementTheme& requestedTheme)
 {
 }
 
+NonClientIslandWindow::~NonClientIslandWindow()
+{
+    Close();
+}
+
 void NonClientIslandWindow::Close()
 {
     // Avoid further callbacks into XAML/WinUI-land after we've Close()d the DesktopWindowXamlSource

src/cascadia/WindowsTerminal/NonClientIslandWindow.h

@@ -30,6 +30,7 @@ class NonClientIslandWindow : public IslandWindow
     static constexpr const int topBorderVisibleHeight = 1;
 
     NonClientIslandWindow(const winrt::Windows::UI::Xaml::ElementTheme& requestedTheme) noexcept;
+    ~NonClientIslandWindow() override;
 
     void Refrigerate() noexcept override;
 

src/cascadia/WindowsTerminal/WindowEmperor.cpp

@@ -584,15 +584,6 @@ 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/WindowThread.cpp

@@ -4,6 +4,8 @@
 #include "pch.h"
 #include "WindowThread.h"
 
+using namespace winrt::Microsoft::Terminal::Remoting;
+
 WindowThread::WindowThread(winrt::TerminalApp::AppLogic logic,
                            winrt::Microsoft::Terminal::Remoting::WindowRequestedArgs args,
                            winrt::Microsoft::Terminal::Remoting::WindowManager manager,
@@ -81,17 +83,6 @@ void WindowThread::RundownForExit()
     _pumpRemainingXamlMessages();
 }
 
-void WindowThread::ThrowAway()
-{
-    // raise the signal to unblock KeepWarm. We won't have a host, so we'll drop
-    // out of the message loop to eventually RundownForExit.
-    //
-    // This should only be called when the app is fully quitting. After this is
-    // called on any thread, on win10, we won't be able to call into XAML
-    // anymore.
-    _microwaveBuzzer.notify_one();
-}
-
 // Method Description:
 // - Check if we should keep this window alive, to try it's message loop again.
 //   If we were refrigerated for later, then this will block the thread on the
@@ -108,29 +99,24 @@ bool WindowThread::KeepWarm()
         return true;
     }
 
-    // If we're refrigerated, then wait on the microwave signal, which will be
-    // raised when we get re-heated by another thread to reactivate us.
-
-    if (_warmWindow != nullptr)
+    // Even when the _host has been destroyed the HWND will continue receiving messages, in particular WM_DISPATCHNOTIFY at least once a second. This is important to Windows as it keeps your room warm.
+    MSG msg;
+    for (;;)
     {
-        std::unique_lock lock(_microwave);
-        _microwaveBuzzer.wait(lock);
-
-        // If ThrowAway() was called, then the buzzer will be signalled without
-        // setting a new _host. In that case, the app is quitting, for real. We
-        // just want to exit with false.
-        const bool reheated = _host != nullptr;
-        if (reheated)
+        if (!GetMessageW(&msg, nullptr, 0, 0))
+        {
+            return false;
+        }
+        // We're using a single window message (WM_REFRIGERATE) to indicate both
+        // state transitions. In this case, the window is actually being woken up.
+        if (msg.message == AppHost::WM_REFRIGERATE)
         {
             _UpdateSettingsRequestedToken = _host->UpdateSettingsRequested([this]() { _UpdateSettingsRequestedHandlers(); });
             // Re-initialize the host here, on the window thread
             _host->Initialize();
+            return true;
         }
-        return reheated;
-    }
-    else
-    {
-        return false;
+        DispatchMessageW(&msg);
     }
 }
 
@@ -154,24 +140,22 @@ void WindowThread::Refrigerate()
 
 // Method Description:
 // - "Reheat" this thread for reuse. We'll build a new AppHost, and pass in the
-//   existing window to it. We'll then trigger the _microwaveBuzzer, so KeepWarm
-//   (which is on the UI thread) will get unblocked, and we can initialize this
-//   window.
-void WindowThread::Microwave(
-    winrt::Microsoft::Terminal::Remoting::WindowRequestedArgs args,
-    winrt::Microsoft::Terminal::Remoting::Peasant peasant)
+//   existing window to it. We'll then wake up the thread stuck in KeepWarm().
+void WindowThread::Microwave(WindowRequestedArgs args, Peasant peasant)
 {
+    const auto hwnd = _warmWindow->GetInteropHandle();
+
     _peasant = std::move(peasant);
     _args = std::move(args);
 
-    _host = std::make_shared<::AppHost>(_appLogic,
-                                        _args,
-                                        _manager,
-                                        _peasant,
-                                        std::move(_warmWindow));
+    _host = std::make_shared<AppHost>(_appLogic,
+                                      _args,
+                                      _manager,
+                                      _peasant,
+                                      std::move(_warmWindow));
 
     // raise the signal to unblock KeepWarm and start the window message loop again.
-    _microwaveBuzzer.notify_one();
+    PostMessageW(hwnd, AppHost::WM_REFRIGERATE, 0, 0);
 }
 
 winrt::TerminalApp::TerminalWindow WindowThread::Logic()
@@ -198,6 +182,15 @@ int WindowThread::_messagePump()
 
     while (GetMessageW(&message, nullptr, 0, 0))
     {
+        // We're using a single window message (WM_REFRIGERATE) to indicate both
+        // state transitions. In this case, the window is actually being refrigerated.
+        // This will break us out of our main message loop we'll eventually start
+        // the loop in WindowThread::KeepWarm to await a call to Microwave().
+        if (message.message == AppHost::WM_REFRIGERATE)
+        {
+            break;
+        }
+
         // GH#638 (Pressing F7 brings up both the history AND a caret browsing message)
         // The Xaml input stack doesn't allow an application to suppress the "caret browsing"
         // dialog experience triggered when you press F7. Official recommendation from the Xaml

src/cascadia/WindowsTerminal/WindowThread.h

@@ -22,7 +22,6 @@ class WindowThread : public std::enable_shared_from_this<WindowThread>
     void Microwave(
         winrt::Microsoft::Terminal::Remoting::WindowRequestedArgs args,
         winrt::Microsoft::Terminal::Remoting::Peasant peasant);
-    void ThrowAway();
 
     uint64_t PeasantID();
 
@@ -43,8 +42,6 @@ class WindowThread : public std::enable_shared_from_this<WindowThread>
     winrt::event_token _UpdateSettingsRequestedToken;
 
     std::unique_ptr<::IslandWindow> _warmWindow{ nullptr };
-    std::mutex _microwave;
-    std::condition_variable _microwaveBuzzer;
 
     int _messagePump();
     void _pumpRemainingXamlMessages();