code: Create mutexes to prevent Windows (un)installer from continuing

Might fix the problem where people uninstall StreamFX while they still have OBS Studio open with StreamFX loaded. InnoSetup appears to ignore this in /VERYSILENT, so this is an additional guard against that.

source/plugin.cpp

@@ -136,7 +136,6 @@ MODULE_EXPORT void obs_module_unload(void)
 			_streamfx_gfx_opengl.reset();
 		}
 
-
 		DLOG_INFO("Unloaded Version %s", STREAMFX_VERSION_STRING);
 	} catch (std::exception const& ex) {
 		DLOG_ERROR("Unexpected exception in function '%s': %s", __FUNCTION_NAME__, ex.what());

source/windll.cpp

@@ -4,9 +4,25 @@
 
 #include "warning-disable.hpp"
 #include <Windows.h>
+#include <mutex>
 #include "warning-enable.hpp"
 
-BOOL WINAPI DllMain(HINSTANCE, DWORD, LPVOID)
+std::shared_ptr<void> local_mutex;
+std::shared_ptr<void> global_mutex;
+
+BOOL WINAPI DllMain(HINSTANCE, DWORD dwReason, LPVOID)
 {
+	if (dwReason == DLL_PROCESS_ATTACH) {
+		// Prevent installer from progressing while StreamFX is still active.
+		local_mutex  = std::shared_ptr<void>(CreateMutexW(NULL, TRUE, L"Local\\StreamFX-Setup"), [](HANDLE p) {
+            ReleaseMutex(p);
+            CloseHandle(p);
+        });
+		global_mutex = std::shared_ptr<void>(CreateMutexW(NULL, TRUE, L"Global\\StreamFX-Setup"), [](HANDLE p) {
+			ReleaseMutex(p);
+			CloseHandle(p);
+		});
+	}
+
 	return TRUE;
 }