When an application is responding slowly and you switch away from tha…

…t application, NVDA is now much more responsive in other applications in most cases.

This is done by filtering out events from background windows in most cases to avoid freezes when a background app is unresponsive. One hard-coded exception is when background progress bar reporting is enabled, in which case background valueChange events are allowed.
To facilitate this, eventHandler.shouldAcceptEvent was introduced.
eventHandler.requestEvents was also added to request particular events that are blocked by default; e.g. show events from a specific control or certain events even when in the background.
Fixes #3831.

source/IAccessibleHandler.py

@@ -140,6 +140,12 @@ def flushEvents(self):
 #A place to store live IAccessible NVDAObjects, that can be looked up by their window,objectID,childID event params.
 liveNVDAObjectTable=weakref.WeakValueDictionary()
 
+# #3831: Stuff related to deferring of events for foreground changes.
+# See pumpAll for details.
+MAX_FOREGROUND_DEFERS=2
+_deferUntilForegroundWindow = None
+_foregroundDefers = 0
+
 IAccessibleRolesToNVDARoles={
 	oleacc.ROLE_SYSTEM_WINDOW:controlTypes.ROLE_WINDOW,
 	oleacc.ROLE_SYSTEM_CLIENT:controlTypes.ROLE_PANE,
@@ -567,9 +573,15 @@ def winEventCallback(handle,eventID,window,objectID,childID,threadID,timestamp):
 			#Move up the ancestry to find the real mozilla Window and use that
 			if winUser.getClassName(window)=='MozillaDropShadowWindowClass':
 				return
-		#We never want to see foreground events for the Program Manager or Shell (task bar) 
-		if eventID==winUser.EVENT_SYSTEM_FOREGROUND and windowClassName in ("Progman","Shell_TrayWnd"):
-			return
+		if eventID==winUser.EVENT_SYSTEM_FOREGROUND:
+			#We never want to see foreground events for the Program Manager or Shell (task bar) 
+			if windowClassName in ("Progman","Shell_TrayWnd"):
+				return
+			# #3831: Event handling can be deferred if Windows takes a while to change the foreground window.
+			# See pumpAll for details.
+			global _deferUntilForegroundWindow,_foregroundDefers
+			_deferUntilForegroundWindow=window
+			_foregroundDefers=0
 		if windowClassName=="MSNHiddenWindowClass":
 			# HACK: Events get fired by this window in Windows Live Messenger 2009 when it starts.
 			# If we send a WM_NULL to this window at this point (which happens in accessibleObjectFromEvent), Messenger will silently exit (#677).
@@ -632,11 +644,6 @@ def processFocusWinEvent(window,objectID,childID,force=False):
 	# as this is a child control and the SDM MSAA events don't handle child controls.
 	if childID==0 and not windowClassName.startswith('bosa_sdm') and winUser.getClassName(winUser.getAncestor(window,winUser.GA_PARENT)).startswith('bosa_sdm'):
 		return False
-	rootWindow=winUser.getAncestor(window,winUser.GA_ROOT)
-	# If this window is not within the foreground window and this window or its root window is not a popup window, and this window's root window is not the highest in the z-order
-	if not winUser.isDescendantWindow(winUser.getForegroundWindow(),window) and not (winUser.getWindowStyle(window) & winUser.WS_POPUP or winUser.getWindowStyle(rootWindow)&winUser.WS_POPUP) and winUser.getPreviousWindow(rootWindow)!=0: 
-		# This is a focus event from a background window, so ignore it.
-		return False
 	#Notify appModuleHandler of this new foreground window
 	appModuleHandler.update(winUser.getWindowThreadProcessID(window)[0])
 	#If Java access bridge is running, and this is a java window, then pass it to java and forget about it
@@ -751,10 +758,9 @@ def processForegroundWinEvent(window,objectID,childID):
 	return True
 
 def processShowWinEvent(window,objectID,childID):
-	className=winUser.getClassName(window)
-	#For now we only support 'show' event for tooltips, IMM candidates, notification bars  and other specific notification area alerts as otherwize we get flooded
-	# #4741: TTrayAlert is for Skype.
-	if className in ("Frame Notification Bar","tooltips_class32","mscandui21.candidate","mscandui40.candidate","MSCandUIWindow_Candidate","TTrayAlert") and objectID==winUser.OBJID_CLIENT:
+	# eventHandler.shouldAcceptEvent only accepts show events for a few specific cases.
+	# Narrow this further to only accept events for clients or custom objects.
+	if objectID==winUser.OBJID_CLIENT or objectID>0:
 		NVDAEvent=winEventToNVDAEvent(winUser.EVENT_OBJECT_SHOW,window,objectID,childID)
 		if NVDAEvent:
 			eventHandler.queueEvent(*NVDAEvent)
@@ -831,12 +837,31 @@ def initialize():
 			log.error("initialize: could not register callback for event %s (%s)"%(eventType,winEventIDsToNVDAEventNames[eventType]))
 
 def pumpAll():
+	global _deferUntilForegroundWindow,_foregroundDefers
+	if _deferUntilForegroundWindow:
+		# #3831: Sometimes, a foreground event is fired,
+		# but GetForegroundWindow() takes a short while to return this new foreground.
+		if _foregroundDefers<MAX_FOREGROUND_DEFERS and winUser.getForegroundWindow()!=_deferUntilForegroundWindow:
+			# Wait a core cycle before handling events to give the foreground window time to update.
+			core.requestPump()
+			_foregroundDefers+=1
+			return
+		else:
+			# Either the foreground window is now correct
+			# or we've already had the maximum number of defers.
+			# (Sometimes, foreground events are fired even when the foreground hasn't actually changed.)
+			_deferUntilForegroundWindow=None
+
 	#Receive all the winEvents from the limiter for this cycle
 	winEvents=winEventLimiter.flushEvents()
 	focusWinEvents=[]
 	validFocus=False
 	fakeFocusEvent=None
 	for winEvent in winEvents[0-MAX_WINEVENTS:]:
+		# #4001: Ideally, we'd call shouldAcceptEvent in winEventCallback,
+		# but this causes focus issues when starting applications.
+		if not eventHandler.shouldAcceptEvent(winEventIDsToNVDAEventNames[winEvent[0]], windowHandle=winEvent[1]):
+			continue
 		#We want to only pass on one focus event to NVDA, but we always want to use the most recent possible one 
 		if winEvent[0] in (winUser.EVENT_OBJECT_FOCUS,winUser.EVENT_SYSTEM_FOREGROUND):
 			focusWinEvents.append(winEvent)

source/_UIAHandler.py

@@ -188,6 +188,12 @@ def IUIAutomationEventHandler_HandleAutomationEvent(self,sender,eventID):
 			return
 		if not self.isNativeUIAElement(sender):
 			return
+		try:
+			window=sender.cachedNativeWindowHandle
+		except COMError:
+			window=None
+		if window and not eventHandler.shouldAcceptEvent(NVDAEventName,windowHandle=window):
+			return
 		import NVDAObjects.UIA
 		obj=NVDAObjects.UIA.UIA(UIAElement=sender)
 		if not obj or (NVDAEventName=="gainFocus" and not obj.shouldAllowUIAFocusEvent):
@@ -217,6 +223,12 @@ def IUIAutomationFocusChangedEventHandler_HandleFocusChangedEvent(self,sender):
 			# Therefore, don't ignore the event if the last focus object has lost its hasKeyboardFocus state.
 			if self.clientObject.compareElements(sender,lastFocus) and lastFocus.currentHasKeyboardFocus:
 				return
+		try:
+			window=sender.cachedNativeWindowHandle
+		except COMError:
+			window=None
+		if window and not eventHandler.shouldAcceptEvent("gainFocus",windowHandle=window):
+			return
 		obj=NVDAObjects.UIA.UIA(UIAElement=sender)
 		if not obj or not obj.shouldAllowUIAFocusEvent:
 			return
@@ -234,6 +246,12 @@ def IUIAutomationPropertyChangedEventHandler_HandlePropertyChangedEvent(self,sen
 			return
 		if not self.isNativeUIAElement(sender):
 			return
+		try:
+			window=sender.cachedNativeWindowHandle
+		except COMError:
+			window=None
+		if window and not eventHandler.shouldAcceptEvent(NVDAEventName,windowHandle=window):
+			return
 		import NVDAObjects.UIA
 		obj=NVDAObjects.UIA.UIA(UIAElement=sender)
 		if not obj:

source/appModuleHandler.py

@@ -138,6 +138,8 @@ def cleanup():
 		if deadMod in set(o.appModule for o in api.getFocusAncestors()+[api.getFocusObject()] if o and o.appModule):
 			if hasattr(deadMod,'event_appLoseFocus'):
 				deadMod.event_appLoseFocus()
+		import eventHandler
+		eventHandler.handleAppTerminate(deadMod)
 		try:
 			deadMod.terminate()
 		except:

source/eventHandler.py

@@ -14,6 +14,8 @@
 import controlTypes
 from logHandler import log
 import globalPluginHandler
+import config
+import winUser
 
 #Some dicts to store event counts by name and or obj
 _pendingEventCountsByName={}
@@ -178,3 +180,82 @@ def doPreDocumentLoadComplete(obj):
 			#Focus may be in this new treeInterceptor, so force focus to look up its treeInterceptor
 			focusObject.treeInterceptor=treeInterceptorHandler.getTreeInterceptor(focusObject)
 	return True
+
+#: set of (eventName, processId, windowClassName) of events to accept.
+_acceptEvents = set()
+#: Maps process IDs to sets of events so they can be cleaned up when the process exits.
+_acceptEventsByProcess = {}
+
+def requestEvents(eventName=None, processId=None, windowClassName=None):
+	"""Request that particular events be accepted from a platform API.
+	Normally, L{shouldAcceptEvent} rejects certain events, including
+	most show events, events indicating changes in background processes, etc.
+	This function allows plugins to override this for specific cases;
+	e.g. to receive show events from a specific control or
+	to receive certain events even when in the background.
+	Note that NVDA may block some events at a lower level and doesn't listen for some event types at all.
+	In these cases, you will not be able to override this.
+	This should generally be called when a plugin is instantiated.
+	All arguments must be provided.
+	"""
+	if not eventName or not processId or not windowClassName:
+		raise ValueError("eventName, processId or windowClassName not specified")
+	entry = (eventName, processId, windowClassName)
+	procEvents = _acceptEventsByProcess.get(processId)
+	if not procEvents:
+		procEvents = _acceptEventsByProcess[processId] = set()
+	procEvents.add(entry)
+	_acceptEvents.add(entry)
+
+def handleAppTerminate(appModule):
+	global _acceptEvents
+	events = _acceptEventsByProcess.pop(appModule.processID, None)
+	if not events:
+		return
+	_acceptEvents -= events
+
+def shouldAcceptEvent(eventName, windowHandle=None):
+	"""Check whether an event should be accepted from a platform API.
+	Creating NVDAObjects and executing events can be expensive
+	and might block the main thread noticeably if the object is slow to respond.
+	Therefore, this should be used before NVDAObject creation to filter out any unnecessary events.
+	A platform API handler may do its own filtering before this.
+	"""
+	if not windowHandle:
+		# We can't filter without a window handle.
+		return True
+	key = (eventName,
+		winUser.getWindowThreadProcessID(windowHandle)[0],
+		winUser.getClassName(windowHandle))
+	if key in _acceptEvents:
+		return True
+	if eventName == "valueChange" and config.conf["presentation"]["progressBarUpdates"]["reportBackgroundProgressBars"]:
+		return True
+	if eventName == "show":
+		# Only accept 'show' events for specific cases, as otherwise we get flooded.
+		return winUser.getClassName(windowHandle) in (
+			"Frame Notification Bar", # notification bars
+			"tooltips_class32", # tooltips
+			"mscandui21.candidate", "mscandui40.candidate", "MSCandUIWindow_Candidate", # IMM candidates
+			"TTrayAlert", # #4741: Skype
+		)
+	if eventName == "alert" and winUser.getClassName(winUser.getAncestor(windowHandle, winUser.GA_PARENT)) == "ToastChildWindowClass":
+		# Toast notifications.
+		return True
+	if windowHandle == winUser.getDesktopWindow():
+		# #3897: We fire some events such as switchEnd and menuEnd on the desktop window
+		# because the original window is now invalid.
+		return True
+
+	fg = winUser.getForegroundWindow()
+	if (winUser.isDescendantWindow(fg, windowHandle)
+			# #3899, #3905: Covers cases such as the Firefox Page Bookmarked window and OpenOffice/LibreOffice context menus.
+			or winUser.isDescendantWindow(fg, winUser.getAncestor(windowHandle, winUser.GA_ROOTOWNER))):
+		# This is for the foreground application.
+		return True
+	if (winUser.user32.GetWindowLongW(windowHandle, winUser.GWL_EXSTYLE) & winUser.WS_EX_TOPMOST
+			or winUser.user32.GetWindowLongW(winUser.getAncestor(windowHandle, winUser.GA_ROOT), winUser.GWL_EXSTYLE) & winUser.WS_EX_TOPMOST):
+		# This window or its root is a topmost window.
+		# This includes menus, combo box pop-ups and the task switching list.
+		return True
+	return False

source/winUser.py

@@ -85,6 +85,7 @@ class GUITHREADINFO(Structure):
 WS_HSCROLL=0x100000
 WS_VSCROLL=0x200000
 WS_CAPTION=0xC00000
+WS_EX_TOPMOST=0x00000008
 BS_GROUPBOX=7
 ES_MULTILINE=4
 LBS_OWNERDRAWFIXED=0x0010
@@ -109,6 +110,7 @@ class GUITHREADINFO(Structure):
 #getWindowLong
 GWL_ID=-12
 GWL_STYLE=-16
+GWL_EXSTYLE=-20
 #getWindow
 GW_HWNDNEXT=2
 GW_HWNDPREV=3

user_docs/en/changes.t2t

@@ -29,10 +29,12 @@
 - In browse mode in Internet Explorer and other MSHTML controls, the correct content is now reported when an element appears or changes and is immediately focused. (#5040)
 - In browse mode in Microsoft Word, single letter navigation now updates the braille display and the review cursor as expected. (#4968)
 - In braille, extraneous spaces are no longer displayed between or after indicators for controls and formatting. (#5043)
+- When an application is responding slowly and you switch away from that application, NVDA is now much more responsive in other applications in most cases. (#3831)
 
 
 == Changes for Developers ==
 - You can now injet raw input from a system keyboard that is not handled natively by Windows (e.g. a QWERTY keyboard on a braille display) using the new keyboardHandler.injectRawKeyboardInput function. (#4576)
+- eventHandler.requestEvents has been added to request particular events that are blocked by default; e.g. show events from a specific control or certain events even when in the background. (#3831)
 
 
 = 2015.2 =