Disable UIA text change events outside of Word, Windows Console, and …

…Windows Terminal (#14067)

Mitigation for #11002.
Blocking #14047.

Summary of the issue:
UIA textChange NVDA events are seldom (if ever) used outside of a few specific situations, but have an extreme performance impact (see #11002).

Description of user facing changes
Improved performance/less chance of NVDA hanging in UIA applications.

Description of development approach
Explicitly do not process UIA textChange events outside of Windows Console, Terminal, and Word. The eventual end goal is to remove TermControl/TermControl2 from UIAHandler.textChangeUIAClassNames in #14047, which will very greatly improve performance in Windows Terminal. (conhost will remain, as there don't seem to be any plans to add notifications, especially as wt is becoming the default).

I'm very reluctant to add a mechanism by which add-ons/app modules can request textChange events unless someone requests it, especially given #11002.

source/UIAHandler/__init__.py

@@ -1,5 +1,5 @@
 # A part of NonVisual Desktop Access (NVDA)
-# Copyright (C) 2008-2021 NV Access Limited, Joseph Lee, Babbage B.V., Leonard de Ruijter, Bill Dengler
+# Copyright (C) 2008-2022 NV Access Limited, Joseph Lee, Babbage B.V., Leonard de Ruijter, Bill Dengler
 # This file is covered by the GNU General Public License.
 # See the file COPYING for more details.
 
@@ -99,6 +99,16 @@
 	"Shell_SystemDialog", # Various dialogs in Windows 10 Settings app
 ]
 
+textChangeUIAAutomationIDs = (
+	"Text Area",  # Windows Console Host
+)
+
+textChangeUIAClassNames = (
+	"_WwG",  # Microsoft Word
+	"TermControl",
+	"TermControl2"
+)
+
 NVDAUnitsToUIAUnits: Dict[str, int] = {
 	textInfos.UNIT_CHARACTER: UIA.TextUnit_Character,
 	textInfos.UNIT_WORD: UIA.TextUnit_Word,
@@ -206,11 +216,9 @@
 autoSelectDetectionAvailable = False
 if winVersion.getWinVer() >= winVersion.WIN10:
 	UIAEventIdsToNVDAEventNames.update({
-		UIA.UIA_Text_TextChangedEventId: "textChange",
 		UIA.UIA_Text_TextSelectionChangedEventId: "caret",
 	})
 	localEventHandlerGroupUIAEventIds.update({
-		UIA.UIA_Text_TextChangedEventId,
 		UIA.UIA_Text_TextSelectionChangedEventId,
 	})
 	autoSelectDetectionAvailable = True
@@ -268,6 +276,7 @@ def __init__(self):
 		super(UIAHandler,self).__init__()
 		self.globalEventHandlerGroup = None
 		self.localEventHandlerGroup = None
+		self.localEventHandlerGroupWithTextChanges = None
 		self._localEventHandlerGroupElements = set()
 		self.MTAThreadInitEvent=threading.Event()
 		self.MTAThreadQueue = Queue()
@@ -403,6 +412,17 @@ def _registerGlobalEventHandlers(self):
 				self.baseCacheRequest,
 				self
 			)
+		if (
+			not utils._shouldSelectivelyRegister()
+			and winVersion.getWinVer() >= winVersion.WIN10
+		):
+			# #14067: Due to poor performance, textChange requires special handling
+			self.globalEventHandlerGroup.AddAutomationEventHandler(
+				UIA.UIA_Text_TextChangedEventId,
+				UIA.TreeScope_Subtree,
+				self.baseCacheRequest,
+				self
+			)
 		# #7984: add support for notification event (IUIAutomation5, part of Windows 10 build 16299 and later).
 		if isinstance(self.clientObject, UIA.IUIAutomation5):
 			self.globalEventHandlerGroup.AddNotificationEventHandler(
@@ -421,21 +441,41 @@ def _registerGlobalEventHandlers(self):
 	def _createLocalEventHandlerGroup(self):
 		if isinstance(self.clientObject, UIA.IUIAutomation6):
 			self.localEventHandlerGroup = self.clientObject.CreateEventHandlerGroup()
+			self.localEventHandlerGroupWithTextChanges = self.clientObject.CreateEventHandlerGroup()
 		else:
 			self.localEventHandlerGroup = utils.FakeEventHandlerGroup(self.clientObject)
+			self.localEventHandlerGroupWithTextChanges = utils.FakeEventHandlerGroup(self.clientObject)
 		self.localEventHandlerGroup.AddPropertyChangedEventHandler(
 			UIA.TreeScope_Ancestors | UIA.TreeScope_Element,
 			self.baseCacheRequest,
 			self,
 			*self.clientObject.IntSafeArrayToNativeArray(localEventHandlerGroupUIAPropertyIds)
 		)
+		self.localEventHandlerGroupWithTextChanges.AddPropertyChangedEventHandler(
+			UIA.TreeScope_Ancestors | UIA.TreeScope_Element,
+			self.baseCacheRequest,
+			self,
+			*self.clientObject.IntSafeArrayToNativeArray(localEventHandlerGroupUIAPropertyIds)
+		)
 		for eventId in localEventHandlerGroupUIAEventIds:
 			self.localEventHandlerGroup.AddAutomationEventHandler(
 				eventId,
 				UIA.TreeScope_Ancestors | UIA.TreeScope_Element,
 				self.baseCacheRequest,
 				self
 			)
+			self.localEventHandlerGroupWithTextChanges.AddAutomationEventHandler(
+				eventId,
+				UIA.TreeScope_Ancestors | UIA.TreeScope_Element,
+				self.baseCacheRequest,
+				self
+			)
+		self.localEventHandlerGroupWithTextChanges.AddAutomationEventHandler(
+			UIA.UIA_Text_TextChangedEventId,
+			UIA.TreeScope_Ancestors | UIA.TreeScope_Element,
+			self.baseCacheRequest,
+			self
+		)
 
 	def addEventHandlerGroup(self, element, eventHandlerGroup):
 		if isinstance(eventHandlerGroup, UIA.IUIAutomationEventHandlerGroup):
@@ -466,7 +506,23 @@ def func():
 				if not isStillFocus:
 					return
 			try:
-				self.addEventHandlerGroup(element, self.localEventHandlerGroup)
+				if (
+					element.currentClassName in textChangeUIAClassNames
+					or element.CachedAutomationID in textChangeUIAAutomationIDs
+				):
+					group = self.localEventHandlerGroupWithTextChanges
+					logPrefix = "Explicitly"
+				else:
+					group = self.localEventHandlerGroup
+					logPrefix = "Not"
+
+				if _isDebug():
+					log.debugWarning(
+						f"{logPrefix} registering for textChange events from UIA element "
+						f"with class name {repr(element.currentClassName)} "
+						f"and automation ID {repr(element.CachedAutomationID)}"
+					)
+				self.addEventHandlerGroup(element, group)
 			except COMError:
 				log.error("Could not register for UIA events for element", exc_info=True)
 			else:
@@ -500,7 +556,22 @@ def IUIAutomationEventHandler_HandleAutomationEvent(self,sender,eventID):
 			if _isDebug():
 				log.debug("HandleAutomationEvent: Ignored MenuOpenedEvent while focus event pending")
 			return
-		NVDAEventName=UIAEventIdsToNVDAEventNames.get(eventID,None)
+		if eventID == UIA.UIA_Text_TextChangedEventId:
+			if (
+				sender.currentClassName in textChangeUIAClassNames
+				or sender.CachedAutomationID in textChangeUIAAutomationIDs
+			):
+				NVDAEventName = "textChange"
+			else:
+				if _isDebug():
+					log.debugWarning(
+						"HandleAutomationEvent: Dropping textChange event from element "
+						f"with class name {repr(sender.currentClassName)} "
+						f"and automation ID {repr(sender.CachedAutomationID)}"
+					)
+				return
+		else:
+			NVDAEventName = UIAEventIdsToNVDAEventNames.get(eventID, None)
 		if not NVDAEventName:
 			if _isDebug():
 				log.debugWarning(f"HandleAutomationEvent: Don't know how to handle event {eventID}")

user_docs/en/changes.t2t

@@ -47,6 +47,7 @@ What's New in NVDA
 Please refer to [the developer guide https://www.nvaccess.org/files/nvda/documentation/developerGuide.html#API] for information on NVDA's API deprecation and removal process.
 
 - The [NVDA API Announcement mailing list https://groups.google.com/a/nvaccess.org/g/nvda-api/about] was created. (#13999)
+- NVDA no longer processes ``textChange`` events for most UI Automation applications due to their extreme negative performance impact. (#11002, #14067)
 -