code review updates

Author: atavism

windows/runner/main.cpp

@@ -10,6 +10,11 @@ namespace {
 
 constexpr const wchar_t kSingleInstanceMutexName[] =
     L"Local\\org.getlantern.lantern.single-instance";
+constexpr const wchar_t kSingleInstanceReadyEventName[] =
+    L"Local\\org.getlantern.lantern.window-ready";
+constexpr DWORD kWindowReadyTimeoutMs = 5000;
+constexpr DWORD kActivationRetryTimeoutMs = 1000;
+constexpr DWORD kActivationRetryIntervalMs = 100;
 
 }  // namespace
 
@@ -21,10 +26,14 @@ int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
     CreateAndAttachConsole();
   }
 
+  SingleInstanceReadyEvent window_ready(kSingleInstanceReadyEventName);
   SingleInstanceLock single_instance(kSingleInstanceMutexName);
   if (!single_instance.IsPrimaryInstance()) {
-    ActivateExistingLanternWindow();
-    return EXIT_SUCCESS;
+    window_ready.Wait(kWindowReadyTimeoutMs);
+    return ActivateExistingLanternWindowWithRetry(kActivationRetryTimeoutMs,
+                                                  kActivationRetryIntervalMs)
+               ? EXIT_SUCCESS
+               : EXIT_FAILURE;
   }
   if (ActivateExistingLanternWindow()) {
     return EXIT_SUCCESS;
@@ -48,6 +57,7 @@ int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
     return EXIT_FAILURE;
   }
   window.SetQuitOnClose(true);
+  window_ready.Signal();
 
   ::MSG msg;
   while (::GetMessage(&msg, nullptr, 0, 0)) {

windows/runner/single_instance.cpp

@@ -64,6 +64,29 @@ bool SingleInstanceLock::IsPrimaryInstance() const {
   return is_primary_instance_;
 }
 
+SingleInstanceReadyEvent::SingleInstanceReadyEvent(const wchar_t* event_name) {
+  event_ = CreateEventW(nullptr, TRUE, FALSE, event_name);
+}
+
+SingleInstanceReadyEvent::~SingleInstanceReadyEvent() {
+  if (event_ != nullptr) {
+    CloseHandle(event_);
+  }
+}
+
+void SingleInstanceReadyEvent::Signal() {
+  if (event_ != nullptr) {
+    SetEvent(event_);
+  }
+}
+
+bool SingleInstanceReadyEvent::Wait(DWORD timeout_ms) const {
+  if (event_ == nullptr) {
+    return false;
+  }
+  return WaitForSingleObject(event_, timeout_ms) == WAIT_OBJECT_0;
+}
+
 bool ActivateExistingLanternWindow() {
   HWND existing_window = FindExistingLanternWindow();
   if (existing_window == nullptr) {
@@ -105,3 +128,27 @@ bool ActivateExistingLanternWindow() {
   }
   return true;
 }
+
+bool ActivateExistingLanternWindowWithRetry(DWORD timeout_ms,
+                                            DWORD retry_interval_ms) {
+  const ULONGLONG deadline = GetTickCount64() + timeout_ms;
+
+  do {
+    if (ActivateExistingLanternWindow()) {
+      return true;
+    }
+
+    const ULONGLONG now = GetTickCount64();
+    if (now >= deadline) {
+      break;
+    }
+
+    DWORD sleep_ms = static_cast<DWORD>(deadline - now);
+    if (sleep_ms > retry_interval_ms) {
+      sleep_ms = retry_interval_ms;
+    }
+    Sleep(sleep_ms);
+  } while (true);
+
+  return false;
+}

windows/runner/single_instance.h

@@ -18,6 +18,23 @@ class SingleInstanceLock {
   bool is_primary_instance_ = true;
 };
 
+class SingleInstanceReadyEvent {
+ public:
+  explicit SingleInstanceReadyEvent(const wchar_t* event_name);
+  ~SingleInstanceReadyEvent();
+
+  SingleInstanceReadyEvent(const SingleInstanceReadyEvent&) = delete;
+  SingleInstanceReadyEvent& operator=(const SingleInstanceReadyEvent&) = delete;
+
+  void Signal();
+  bool Wait(DWORD timeout_ms) const;
+
+ private:
+  HANDLE event_ = nullptr;
+};
+
 bool ActivateExistingLanternWindow();
+bool ActivateExistingLanternWindowWithRetry(DWORD timeout_ms,
+                                            DWORD retry_interval_ms);
 
 #endif  // RUNNER_SINGLE_INSTANCE_H_