Don't block an app's main thread when sending typed characters to NVDA

nvdaHelper/interfaces/nvdaControllerInternal/nvdaControllerInternal.idl

@@ -47,10 +47,9 @@ interface NvdaControllerInternal {
 
 /**
  * Notifies NVDA that a character has been typed in this thread.
- * @param threadID the thread the layout change occured in
  * @param ch the character typed.
  */
-	error_status_t __stdcall typedCharacterNotify([in] const long threadID, [in] const wchar_t ch);
+	error_status_t __stdcall typedCharacterNotify([in] const wchar_t ch);
 
 /**
  * Notifies NVDA that text in the given rectangle (in screen coordinates), in the given window, has changed.

nvdaHelper/local/nvdaControllerInternal.c

@@ -24,9 +24,9 @@ error_status_t __stdcall nvdaControllerInternal_inputLangChangeNotify(const long
 	return _nvdaControllerInternal_inputLangChangeNotify(threadID,hkl,layoutString);
 }
 
-error_status_t(__stdcall *_nvdaControllerInternal_typedCharacterNotify)(const long, const wchar_t); 
-error_status_t __stdcall nvdaControllerInternal_typedCharacterNotify(const long threadID, const wchar_t ch) {
-	return _nvdaControllerInternal_typedCharacterNotify(threadID,ch);
+error_status_t(__stdcall *_nvdaControllerInternal_typedCharacterNotify)(const wchar_t); 
+error_status_t __stdcall nvdaControllerInternal_typedCharacterNotify(const wchar_t ch) {
+	return _nvdaControllerInternal_typedCharacterNotify(ch);
 }
 
 

nvdaHelper/remote/injection.cpp

@@ -193,14 +193,32 @@ DWORD WINAPI inprocMgrThreadFunc(LPVOID data) {
 	// Even though we only registered for in-context winEvents, we may still receive some out-of-context events; e.g. console events.
 	// Therefore, we must have a message loop.
 	// Otherwise, any out-of-context events will cause major lag which increases over time.
-	do {
-		// Consume and handle all pending messages.
-		MSG msg;
-		while(PeekMessage(&msg,NULL,0,0,PM_REMOVE)) {
-			TranslateMessage(&msg);
-			DispatchMessage(&msg);
+	// We must also wait in an alertable state so that any APC functions queued to this thread by other NVDAHelper code will be executed.
+	while(true) {
+		const long handleCount = 1;
+		const long WAIT_PENDING_MESSAGES = WAIT_OBJECT_0 + handleCount;
+		DWORD res = MsgWaitForMultipleObjectsEx(
+			handleCount,
+			&nvdaUnregisteredEvent,
+			INFINITE,
+			QS_ALLINPUT,
+			MWMO_ALERTABLE // wait in an alert state so queued APC functions are executed.
+		);
+		if(res == WAIT_PENDING_MESSAGES) {
+			// Consume and handle all pending messages.
+			MSG msg;
+			while(PeekMessage(&msg, nullptr, 0, 0, PM_REMOVE)) {
+				TranslateMessage(&msg);
+				DispatchMessage(&msg);
+			}
+			continue;
+		} else if(res == WAIT_IO_COMPLETION) {
+			// Woke for a queued APC function. Keep going.
+			continue;
 		}
-	} while(MsgWaitForMultipleObjects(1,&nvdaUnregisteredEvent,FALSE,INFINITE,QS_ALLINPUT)==WAIT_OBJECT_0+1);
+		// anything else (the registrationEvent was set, there was an error) means we need to stop.
+		break;
+	}
 	nhAssert(inprocMgrThreadHandle);
 	inprocThreadsLock.acquire();
 	CloseHandle(inprocMgrThreadHandle);

nvdaHelper/remote/nvdaHelperRemote.h

@@ -66,4 +66,7 @@ bool registerWindowsHook(int hookType, HOOKPROC hookProc);
  */
 bool unregisterWindowsHook(int hookType, HOOKPROC hookProc);
 
+// The handle for NVDA's inproc manager thread
+extern HANDLE inprocMgrThreadHandle;
+
 #endif

nvdaHelper/remote/typedCharacter.cpp

@@ -21,14 +21,22 @@ This license can be found at:
 
 HWND typedCharacter_window=NULL;
 
+void __stdcall typedCharacter_apcFunc(ULONG_PTR data) {
+	nvdaControllerInternal_typedCharacterNotify(static_cast<wchar_t>(data));
+}
+
 LRESULT CALLBACK typedCharacter_getMessageHook(int code, WPARAM wParam, LPARAM lParam) {
 	static WPARAM lastCharacter=0;
 	MSG* pmsg=(MSG*)lParam;
 	if(pmsg->message==WM_KEYDOWN) {
 		typedCharacter_window=pmsg->hwnd;
 		lastCharacter=0;
 	} else if((typedCharacter_window!=0)&&(pmsg->message==WM_CHAR)&&(pmsg->hwnd==typedCharacter_window)&&(pmsg->wParam!=lastCharacter)) { 
-		nvdaControllerInternal_typedCharacterNotify(GetCurrentThreadId(),static_cast<wchar_t>(pmsg->wParam));
+		// Instruct NVDA's inproc manager thread to report the typed character to NVDA via rpc.
+
+		// If we were to call the rpc function directly, it might cause a deadlock
+		// if NvDA were to interact with this app's main thread while the rpc function was in progress.
+		QueueUserAPC(typedCharacter_apcFunc, inprocMgrThreadHandle, static_cast<ULONG_PTR>(pmsg->wParam));
 		lastCharacter=pmsg->wParam;
 	}
 	return 0;

source/NVDAHelper.py

@@ -13,6 +13,11 @@
 import config
 
 from ctypes import *
+from ctypes import (
+	WINFUNCTYPE,
+	c_long,
+	c_wchar,
+)
 from ctypes.wintypes import *
 from comtypes import BSTR
 import winUser
@@ -394,8 +399,9 @@ def nvdaControllerInternal_inputLangChangeNotify(threadID,hkl,layoutString):
 	queueHandler.queueFunction(queueHandler.eventQueue,ui.message,msg)
 	return 0
 
-@WINFUNCTYPE(c_long,c_long,c_wchar)
-def nvdaControllerInternal_typedCharacterNotify(threadID,ch):
+
+@WINFUNCTYPE(c_long, c_wchar)
+def nvdaControllerInternal_typedCharacterNotify(ch):
 	focus=api.getFocusObject()
 	if focus.windowClassName!="ConsoleWindowClass":
 		eventHandler.queueEvent("typedCharacter", focus, ch=ch)