Use mutex to force single instance.

src/windows/InstanceMutex.cpp

@@ -0,0 +1,32 @@
+#include "InstanceMutex.hpp"
+
+void InstanceMutex::Close()
+{
+	if (m_handle)
+	{
+		CloseHandle(m_handle);
+		m_handle = NULL;
+	}
+}
+
+HRESULT InstanceMutex::Init()
+{
+#ifdef DISABLE_SINGLE_INSTANCE
+	return 0;
+#else
+
+	SetLastError(NO_ERROR);
+	m_handle = CreateMutex(NULL, TRUE, L"DiscordMessenger");
+
+	const DWORD error = GetLastError();
+	if (error == ERROR_ALREADY_EXISTS)
+		Close();
+
+	return error;
+#endif
+}
+
+InstanceMutex::~InstanceMutex()
+{
+	Close();
+}

src/windows/InstanceMutex.hpp

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <windows.h>
+
+class InstanceMutex
+{
+private:
+	HANDLE m_handle = NULL;
+
+	void Close();
+
+public:
+	HRESULT Init();
+	~InstanceMutex();
+};

src/windows/Main.cpp

@@ -25,11 +25,11 @@
 #include "ProgressDialog.hpp"
 #include "AutoComplete.hpp"
 #include "ShellNotification.hpp"
+#include "InstanceMutex.hpp"
 #include "../discord/LocalSettings.hpp"
 #include "../discord/WebsocketClient.hpp"
 #include "../discord/UpdateChecker.hpp"
 
-#include <tlhelp32.h>
 #include <system_error>
 
 // proportions:
@@ -1437,7 +1437,7 @@ LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
 			GetShellNotification()->Callback(wParam, lParam);
 			break;
 		}
-		case SW_RESTORE:
+		case WM_RESTORE:
 			GetFrontend()->RestoreWindow();
 			break;
 	}
@@ -1573,59 +1573,28 @@ HTTPClient* GetHTTPClient()
 	return g_pHTTPClient;
 }
 
-//https://stackoverflow.com/a/48207646
-static void GetAllWindowsFromProcessID(const DWORD dwProcessID, std::vector <HWND>& vhWnds)
-{
-	HWND hCurWnd = NULL;
-	do
-	{
-		hCurWnd = FindWindowEx(NULL, hCurWnd, NULL, NULL);
-		DWORD dwProcID = 0;
-		GetWindowThreadProcessId(hCurWnd, &dwProcID);
-		if (dwProcID == dwProcessID)
-		{
-			vhWnds.push_back(hCurWnd);
-		}
-	} while (hCurWnd != NULL);
-}
+InstanceMutex g_instanceMutex;
 
-static bool CheckExistingProcesses()
+static bool ForceSingleInstance(LPCWSTR pClassName)
 {
-	TCHAR fileNameRaw[MAX_PATH];
-	GetModuleFileName(NULL, fileNameRaw, MAX_PATH);
-	TCHAR* fileName = PathFindFileName(fileNameRaw);
-
-	PROCESSENTRY32 processEntry32;
-	processEntry32.dwSize = sizeof(PROCESSENTRY32);
+	HRESULT hResult = g_instanceMutex.Init();
 
-	HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
-	const DWORD selfPid = GetCurrentProcessId();
+	if (hResult != ERROR_ALREADY_EXISTS)
+		return false;
 
-	if (Process32First(snapshot, &processEntry32))
+	HWND hWnd = FindWindow(pClassName, NULL);
+	if (hWnd)
 	{
-		while (Process32Next(snapshot, &processEntry32))
-		{
-			if (!_tcscmp(processEntry32.szExeFile, fileName) && processEntry32.th32ProcessID != selfPid)
-			{
-				std::vector<HWND> windows;
-				GetAllWindowsFromProcessID(processEntry32.th32ProcessID, windows);
-
-				for (HWND window : windows) {
-					SendMessage(window, SW_RESTORE, 0, 0);
-				}
-
-				return true;
-			}
-		}
+		SendMessage(hWnd, WM_RESTORE, 0, 0);
 	}
-
-	CloseHandle(snapshot);
-	return false;
+	return true;
 }
 
 int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR pCmdLine, int nShowCmd)
 {
-	if (CheckExistingProcesses())
+	LPCWSTR pClassName = TEXT("DiscordMessengerClass");
+
+	if (ForceSingleInstance(pClassName))
 		return 0;
 
 	g_hInstance = hInstance;
@@ -1657,7 +1626,7 @@ int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR pCmdLin
 
 	wc.lpfnWndProc   = WindowProc;
 	wc.hInstance     = hInstance;
-	wc.lpszClassName = TEXT("DiscordMessengerClass");
+	wc.lpszClassName = pClassName;
 	wc.hbrBackground = g_backgroundBrush;
 	wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
 	wc.hIcon         = g_Icon = LoadIcon(hInstance, MAKEINTRESOURCE(DMIC(IDI_ICON)));

src/windows/WindowMessages.hpp

@@ -67,4 +67,5 @@ enum eWmUserMsgs
 	WM_RECREATEMEMBERLIST,
 
 	WM_UPDATETEXTSIZE = WM_APP, // used by the MessageEditor
+	WM_RESTORE,
 };

vs/DiscordMessenger.vcxproj

@@ -504,6 +504,7 @@
     <ClInclude Include="..\src\windows\GuildLister.hpp" />
     <ClInclude Include="..\src\windows\ImageLoader.hpp" />
     <ClInclude Include="..\src\windows\ImageViewer.hpp" />
+    <ClInclude Include="..\src\windows\InstanceMutex.hpp" />
     <ClInclude Include="..\src\windows\LoadingMessage.hpp" />
     <ClInclude Include="..\src\windows\LogonDialog.hpp" />
     <ClInclude Include="..\src\windows\Main.hpp" />
@@ -568,6 +569,7 @@
     <ClCompile Include="..\src\windows\GuildLister.cpp" />
     <ClCompile Include="..\src\windows\ImageLoader.cpp" />
     <ClCompile Include="..\src\windows\ImageViewer.cpp" />
+    <ClCompile Include="..\src\windows\InstanceMutex.cpp" />
     <ClCompile Include="..\src\windows\LoadingMessage.cpp" />
     <ClCompile Include="..\src\windows\LogonDialog.cpp" />
     <ClCompile Include="..\src\windows\Main.cpp" />

vs/DiscordMessenger.vcxproj.filters

@@ -629,6 +629,9 @@
     <ClInclude Include="..\src\discord\DiscordClientConfig.hpp">
       <Filter>Header Files\Discord</Filter>
     </ClInclude>
+    <ClInclude Include="..\src\windows\InstanceMutex.hpp">
+      <Filter>Header Files\Windows</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="..\src\windows\ProfileView.cpp">
@@ -799,5 +802,8 @@
     <ClCompile Include="..\src\discord\DiscordClientConfig.cpp">
       <Filter>Source Files\Discord</Filter>
     </ClCompile>
+    <ClCompile Include="..\src\windows\InstanceMutex.cpp">
+      <Filter>Source Files\Windows</Filter>
+    </ClCompile>
   </ItemGroup>
 </Project>