[AlwaysOnTop] Proof of concept (#14360)

Co-authored-by: Niels Laute <niels.laute@live.nl>

src/modules/alwaysontop/AlwaysOnTop/main.cpp

@@ -0,0 +1,62 @@
+#include "pch.h"
+
+#include <common/utils/ProcessWaiter.h>
+#include <common/utils/window.h>
+#include <common/utils/UnhandledExceptionHandler_x64.h>
+
+#include <common/utils/logger_helper.h>
+
+#include <AlwaysOnTop.h>
+#include <trace.h>
+
+// Non-localizable
+const std::wstring moduleName = L"AlwaysOnTop";
+const std::wstring internalPath = L"";
+const std::wstring instanceMutexName = L"Local\\PowerToys_AlwaysOnTop_InstanceMutex";
+
+int WINAPI wWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ PWSTR lpCmdLine, _In_ int nCmdShow)
+{
+    winrt::init_apartment();
+    LoggerHelpers::init_logger(moduleName, internalPath, LogSettings::alwaysOnTopLoggerName);
+    InitUnhandledExceptionHandler_x64();    
+
+    auto mutex = CreateMutex(nullptr, true, instanceMutexName.c_str());
+    if (mutex == nullptr)
+    {
+        Logger::error(L"Failed to create mutex. {}", get_last_error_or_default(GetLastError()));
+    }
+
+    if (GetLastError() == ERROR_ALREADY_EXISTS)
+    {
+        return 0;
+    }
+
+    std::wstring pid = std::wstring(lpCmdLine);
+    if (!pid.empty())
+    {
+        auto mainThreadId = GetCurrentThreadId();
+        ProcessWaiter::OnProcessTerminate(pid, [mainThreadId](int err) {
+            if (err != ERROR_SUCCESS)
+            {
+                Logger::error(L"Failed to wait for parent process exit. {}", get_last_error_or_default(err));
+            }
+            else
+            {
+                Logger::trace(L"PowerToys runner exited.");
+            }
+
+            Logger::trace(L"Exiting AlwaysOnTop");
+            PostThreadMessage(mainThreadId, WM_QUIT, 0, 0);
+        });
+    }
+
+    Trace::RegisterProvider();
+
+    AlwaysOnTop app;
+
+    run_message_loop();
+
+    Trace::UnregisterProvider();
+    
+    return 0;
+}