perf: throttle all window/app ax calls

src/api-wrappers/AXUIElement.swift

@@ -15,8 +15,12 @@ extension AXUIElement {
     private static let axCallsRetriesQueueTimeoutInSeconds = Float(6)
     // once an app is unresponsive, let's ignore other AX calls for it to avoid congestion
     private static var axCallsRetriesQueueUnresponsiveAppsMap = ConcurrentMap<String, UInt64>()
-    // some events like window resizing trigger in quick succession. We debounce those
+    private static var throttleMap = ConcurrentMap<String, ThrottleState>()
-    private static var eventsDebounceMap = ConcurrentMap<String, DispatchWorkItem>()
+
+    private struct ThrottleState {
+        let time: UInt64
+        var tailScheduled: Bool
+    }
 
     static func setGlobalTimeout() {
         AXUIElementSetMessagingTimeout(AXUIElementCreateSystemWide(), globalMessagingTimeoutInSeconds)
@@ -31,73 +35,70 @@ extension AXUIElement {
     }
 
     /// if the window server is busy, it may not reply to AX calls. We retry right before the call times-out and returns a bogus value
-    static func retryAxCallUntilTimeout(file: String = #file, function: String = #function, line: Int = #line, context: String = "", after: DispatchTime? = nil, debounceType: DebounceType? = nil, pid: pid_t? = nil, wid: CGWindowID? = nil, retriesQueue: Bool = false, startTimeInNanoseconds: UInt64 = DispatchTime.now().uptimeNanoseconds, callType: AXCallType, block: @escaping () throws -> Void) {
+    static func retryAxCallUntilTimeout(file: String = #file, function: String = #function, line: Int = #line, context: String = "", after: DispatchTime? = nil, pid: pid_t? = nil, wid: CGWindowID? = nil, retriesQueue: Bool = false, startTimeInNanoseconds: UInt64 = DispatchTime.now().uptimeNanoseconds, callType: AXCallType, block: @escaping () throws -> Void) {
-        let closure = { retryAxCallUntilTimeout_(file: file, function: function, line: line, context: context, after: after, debounceType: debounceType, pid: pid, wid: wid, retriesQueue: retriesQueue, startTimeInNanoseconds: startTimeInNanoseconds, callType: callType, block: block) }
+        let closure = { retryAxCallUntilTimeout_(file: file, function: function, line: line, context: context, after: after, pid: pid, wid: wid, retriesQueue: retriesQueue, startTimeInNanoseconds: startTimeInNanoseconds, callType: callType, block: block) }
-        let queue = callType == .updateAppWindows ? BackgroundWork.axCallsManualDiscoveryQueue : (retriesQueue ? BackgroundWork.axCallsRetriesQueue : BackgroundWork.axCallsFirstAttemptQueue)
+        let queue = (callType == .updateAppWindows ? BackgroundWork.axCallsManualDiscoveryQueue
+            : (retriesQueue ? BackgroundWork.axCallsRetriesQueue
+                : BackgroundWork.axCallsFirstAttemptQueue))!
+        if callType == .updateWindowFromAxEvent || callType == .updateWindowFromManualDiscovery {
+            guard let wid else { Logger.error { (callType, context, file, function, line) }; return }
+            if throttleOrProceed(key: "\(callType.rawValue)-wid-\(wid)", queue: queue, closure: closure) { return }
+        }
+        if callType == .updateApp || callType == .updateAppWindows || callType == .updateAppFocusedWindow {
+            guard let pid else { Logger.error { (callType, context, file, function, line) }; return }
+            if throttleOrProceed(key: "\(callType.rawValue)-pid-\(pid)", queue: queue, closure: closure) { return }
+        }
         if let after {
-            queue!.addOperationAfter(deadline: after, block: closure)
+            queue.addOperationAfter(deadline: after, block: closure)
-        } else if let debounceType, let wid {
-            let debounceMapKey = "\(debounceType.rawValue)\(wid)"
-            let workItem = DispatchWorkItem {
-                closure()
-                eventsDebounceMap.withLock { $0[debounceMapKey] = nil }
-            }
-            eventsDebounceMap.withLock {
-                $0[debounceMapKey]?.cancel()
-                $0[debounceMapKey] = workItem
-            }
-            queue!.addOperationAfter(deadline: .now() + humanPerceptionDelay) {
-                workItem.perform()
-            }
         } else {
-            queue!.addOperation(closure)
+            queue.addOperation(closure)
         }
     }
 
-    private static func retryAxCallUntilTimeout_(file: String, function: String, line: Int, context: String, after: DispatchTime?, debounceType: DebounceType?, pid: pid_t?, wid: CGWindowID?, retriesQueue: Bool, startTimeInNanoseconds: UInt64, callType: AXCallType, block: @escaping () throws -> Void) {
+    private static func retryAxCallUntilTimeout_(file: String, function: String, line: Int, context: String, after: DispatchTime?, pid: pid_t?, wid: CGWindowID?, retriesQueue: Bool, startTimeInNanoseconds: UInt64, callType: AXCallType, block: @escaping () throws -> Void) {
         // attempt the AX call
         if (try? block()) != nil {
             return
         }
-        // do we already have ongoing retries for this pid? The app is likely unresponsive
+        // give up?
-        // if their are common updates, we avoid congestion by only retrying the latest update
-        if let pid, callType == .updateWindow || callType == .updateAppWindows {
-            let unresponsiveAppsMapKey = "\(callType.rawValue)\(pid)"
-            let time = axCallsRetriesQueueUnresponsiveAppsMap.withLock { $0[unresponsiveAppsMapKey] }
-            if let time {
-                if startTimeInNanoseconds > time {
-                    // new most recent call; replace and retry
-                    axCallsRetriesQueueUnresponsiveAppsMap.withLock { $0[unresponsiveAppsMapKey] = startTimeInNanoseconds }
-                } else if startTimeInNanoseconds == time {
-                    // most recent call; retry
-                } else {
-                    // old call which has been replaced; ignore
-                    return
-                }
-            } else {
-                // first call; set and retry
-                axCallsRetriesQueueUnresponsiveAppsMap.withLock { $0[unresponsiveAppsMapKey] = startTimeInNanoseconds }
-            }
-        }
-        // should we give up?
         let timePassedInSeconds = Float(DispatchTime.now().uptimeNanoseconds - startTimeInNanoseconds) / 1_000_000_000
         if timePassedInSeconds >= axCallsRetriesQueueTimeoutInSeconds {
             Logger.info { "AX call failed for more than \(Int(axCallsRetriesQueueTimeoutInSeconds))s. Giving up on it. \(logFromContext(file, function, line, context, callType))" }
-            if let pid, callType == .updateWindow || callType == .updateAppWindows {
-                let unresponsiveAppsMapKey = "\(callType.rawValue)\(pid)"
-                axCallsRetriesQueueUnresponsiveAppsMap.withLock { $0.removeValue(forKey: unresponsiveAppsMapKey) }
-            }
             return
         }
         // retry
         Logger.debug { "(pid:\(pid) wid:\(wid)) \(logFromContext(file, function, line, context, callType))" }
-        retryAxCallUntilTimeout(file: file, function: function, line: line, context: context, after: .now() + humanPerceptionDelay, debounceType: debounceType, pid: pid, wid: wid, retriesQueue: true, startTimeInNanoseconds: startTimeInNanoseconds, callType: callType, block: block)
+        retryAxCallUntilTimeout(file: file, function: function, line: line, context: context, after: .now() + humanPerceptionDelay, pid: pid, wid: wid, retriesQueue: true, startTimeInNanoseconds: startTimeInNanoseconds, callType: callType, block: block)
     }
 
     private static func logFromContext(_ file: String, _ function: String, _ line: Int, _ context: String, _ callType: AXCallType) -> String {
         return "Context: \((file as NSString).lastPathComponent):\(line) \(function) \(String(describing: callType)) \(context)"
     }
 
+    private static func throttleOrProceed(key: String, queue: LabeledOperationQueue, closure: @escaping () -> Void) -> Bool {
+        let windowNs: UInt64 = 1_000_000_000
+        return throttleMap.withLock { map in
+            let now = DispatchTime.now().uptimeNanoseconds
+            if let state = map[key] {
+                let elapsed = now >= state.time ? (now - state.time) : windowNs // treat “time in future” as throttled
+                if elapsed < windowNs {
+                    if !state.tailScheduled {
+                        map[key] = ThrottleState(time: state.time, tailScheduled: true)
+
+                        let remaining = windowNs - elapsed
+                        queue.addOperationAfter(deadline: .now() + .nanoseconds(Int(remaining))) {
+                            throttleMap.withLock { $0[key] = nil }
+                            closure()
+                        }
+                    }
+                    return true
+                }
+            }
+            map[key] = ThrottleState(time: now, tailScheduled: false)
+            return false
+        }
+    }
+
     @discardableResult
     func subscribeToNotification(_ axObserver: AXObserver, _ notification: String, _ callback: (() -> Void)? = nil) throws -> Bool {
         let result = AXObserverAddNotification(axObserver, self, notification as CFString, nil)
@@ -116,7 +117,10 @@ extension AXUIElement {
         case subscribeToAppNotification
         case subscribeToWindowNotification
         case subscribeToDockNotification
-        case updateWindow
+        case updateWindowFromAxEvent
+        case updateWindowFromManualDiscovery
+        case updateApp
+        case updateAppFocusedWindow
         case updateAppWindows
         case updateDockBadges
         case axEventEntrypoint
@@ -316,8 +320,3 @@ struct AXAttributes {
     var position: CGPoint?
     var size: CGSize?
 }
-
-enum DebounceType: Int {
-    case windowResizedOrMoved
-    case windowTitleChanged
-}

src/logic/Application.swift

@@ -167,23 +167,29 @@ class Application: NSObject {
                 return
             }
             for axWindow in axWindows {
-                let wid = try axWindow.cgWindowId()
+                guard let wid = try? axWindow.cgWindowId() else { continue }
-                guard wid != 0 && wid != App.app.thumbnailsPanel.windowNumber  else { continue } // some bogus "windows" have wid 0
+                AXUIElement.retryAxCallUntilTimeout(context: debugId, pid: pid, wid: wid, callType: .updateWindowFromManualDiscovery) { [weak self] in
-                let level = wid.level()
+                    try self?.manuallyUpdateWindow(axWindow, wid)
-                let a = try axWindow.attributes([kAXTitleAttribute, kAXSubroleAttribute, kAXRoleAttribute, kAXSizeAttribute, kAXPositionAttribute, kAXFullscreenAttribute, kAXMinimizedAttribute])
-                DispatchQueue.main.async { [weak self] in
-                    guard let self else { return }
-                    let findOrCreate = Windows.findOrCreate(axWindow, wid, self, level, a.title, a.subrole, a.role, a.size, a.position, a.isFullscreen, a.isMinimized)
-                    guard let window = findOrCreate.0 else { return }
-                    if findOrCreate.1 {
-                        Logger.info { "manuallyUpdateWindows found a new window:\(window.debugId)" }
-                        App.app.refreshOpenUiAfterExternalEvent([window])
-                    }
                 }
             }
         }
     }
 
+    func manuallyUpdateWindow(_ axWindow: AXUIElement, _ wid: CGWindowID) throws {
+        guard wid != 0 && wid != App.app.thumbnailsPanel.windowNumber else { return } // some bogus "windows" have wid 0
+        let level = wid.level()
+        let a = try axWindow.attributes([kAXTitleAttribute, kAXSubroleAttribute, kAXRoleAttribute, kAXSizeAttribute, kAXPositionAttribute, kAXFullscreenAttribute, kAXMinimizedAttribute])
+        DispatchQueue.main.async { [weak self] in
+            guard let self else { return }
+            let findOrCreate = Windows.findOrCreate(axWindow, wid, self, level, a.title, a.subrole, a.role, a.size, a.position, a.isFullscreen, a.isMinimized)
+            guard let window = findOrCreate.0 else { return }
+            if findOrCreate.1 {
+                Logger.info { "manuallyUpdateWindows found a new window:\(window.debugId)" }
+                App.app.refreshOpenUiAfterExternalEvent([window])
+            }
+        }
+    }
+
     @discardableResult
     func addWindowlessWindowIfNeeded() -> Window? {
         guard runningApplication.activationPolicy == .regular && !runningApplication.isTerminated

src/logic/Window.swift

@@ -87,12 +87,12 @@ class Window {
     private func observeEvents() {
         AXObserverCreate(application.pid, AccessibilityEvents.axObserverCallback, &axObserver)
         guard let axObserver else { return }
-        AXUIElement.retryAxCallUntilTimeout(context: debugId, pid: application.pid, callType: .subscribeToWindowNotification) { [weak self] in
+        AXUIElement.retryAxCallUntilTimeout(context: debugId, pid: application.pid, wid: cgWindowId, callType: .subscribeToWindowNotification) { [weak self] in
             guard let self else { return }
             if try self.axUiElement!.subscribeToNotification(axObserver, Window.notifications.first!) {
                 Logger.debug { "Subscribed to window: \(self.debugId)" }
                 for notification in Window.notifications.dropFirst() {
-                    AXUIElement.retryAxCallUntilTimeout(context: self.debugId, pid: self.application.pid, callType: .subscribeToWindowNotification) { [weak self] in
+                    AXUIElement.retryAxCallUntilTimeout(context: self.debugId, pid: self.application.pid, wid: cgWindowId, callType: .subscribeToWindowNotification) { [weak self] in
                         try self?.axUiElement!.subscribeToNotification(axObserver, notification)
                     }
                 }
@@ -315,7 +315,7 @@ class Window {
     /// some apps will not trigger AXApplicationActivated, where we usually update application.focusedWindow
     /// workaround: we check and possibly do it here
     private func checkIfFocused() {
-        AXUIElement.retryAxCallUntilTimeout(context: debugId, pid: application.pid, callType: .updateWindow) { [weak self] in
+        AXUIElement.retryAxCallUntilTimeout(context: debugId, pid: application.pid, wid: cgWindowId, callType: .updateAppFocusedWindow) { [weak self] in
             guard let self,
                   let focusedWindow = try self.application.axUiElement?.attributes([kAXFocusedWindowAttribute]).focusedWindow,
                   let window = try (Windows.list.first { $0.isEqualRobust(focusedWindow, (try focusedWindow.cgWindowId())) }) else { return }

src/logic/Windows.swift

@@ -10,7 +10,7 @@ class Windows {
     static func updateIsFullscreenOnCurrentSpace() {
         let windowsOnCurrentSpace = list.filter { !$0.isWindowlessApp }
         for window in windowsOnCurrentSpace {
-            AXUIElement.retryAxCallUntilTimeout(context: window.debugId, after: .now() + humanPerceptionDelay, callType: .updateWindow) { [weak window] in
+            AXUIElement.retryAxCallUntilTimeout(context: window.debugId, after: .now() + humanPerceptionDelay, wid: window.cgWindowId, callType: .updateWindowFromAxEvent) { [weak window] in
                 guard let window else { return }
                 // we reuse existing code, to update .isFullscreen, as if there was a kAXWindowResizedNotification
                 try AccessibilityEvents.handleEventWindow(kAXWindowResizedNotification, window.cgWindowId!, window.application.pid, window.axUiElement!)

src/logic/events/AccessibilityEvents.swift

@@ -15,34 +15,40 @@ class AccessibilityEvents {
         let pid = try element.pid()
         Logger.debug { "\(type) pid:\(pid)" }
         if [kAXApplicationActivatedNotification, kAXApplicationHiddenNotification, kAXApplicationShownNotification].contains(type) {
-            try handleEventApp(type, pid, element)
+            AXUIElement.retryAxCallUntilTimeout(context: "(pid:\(pid))", pid: pid, callType: .updateApp) {
+                try handleEventApp(type, pid, element)
+            }
         } else {
-            try handleEventWindowWithDebounceIfNecessary(type, pid, element)
+            let wid = try element.cgWindowId()
+            AXUIElement.retryAxCallUntilTimeout(context: "(pid:\(pid))", pid: pid, wid: wid, callType: .updateWindowFromAxEvent) {
+                try handleEventWindow(type, wid, pid, element)
+            }
         }
     }
 
     private static func handleEventApp(_ type: String, _ pid: pid_t, _ element: AXUIElement) throws {
         let appFocusedWindow = try element.attributes([kAXFocusedWindowAttribute]).focusedWindow
+        let wid = try appFocusedWindow?.cgWindowId()
         DispatchQueue.main.async {
             guard let app = Applications.findOrCreate(pid) else { return }
             Logger.info { "\(type) app:\(app.debugId)" }
             if type == kAXApplicationActivatedNotification {
-                applicationActivated(app, pid, type, appFocusedWindow)
+                applicationActivated(app, pid, type, appFocusedWindow, wid)
             } else if type == kAXApplicationHiddenNotification || type == kAXApplicationShownNotification {
                 applicationHiddenOrShown(app, pid, type)
             }
         }
     }
 
-    private static func applicationActivated(_ app: Application, _ pid: pid_t, _ type: String, _ appFocusedWindow: AXUIElement?) {
+    private static func applicationActivated(_ app: Application, _ pid: pid_t, _ type: String, _ appFocusedWindow: AXUIElement?, _ wid: CGWindowID?) {
         Applications.frontmostPid = pid
         if app.hasBeenActiveOnce != true {
             app.hasBeenActiveOnce = true
         }
-        if let appFocusedWindow {
+        if let appFocusedWindow, let wid {
             // if there is a focusedWindow, we reuse existing code to process it as if it was a kAXFocusedWindowChangedNotification
-            AXUIElement.retryAxCallUntilTimeout(context: "(type:\(type)", callType: .axEventEntrypoint) {
+            AXUIElement.retryAxCallUntilTimeout(context: "\(type) \(app.debugId))", pid: pid, wid: wid, callType: .updateWindowFromAxEvent) {
-                try handleEventWindowWithDebounceIfNecessary(kAXFocusedWindowChangedNotification, pid, appFocusedWindow)
+                try handleEventWindow(kAXFocusedWindowChangedNotification, wid, pid, appFocusedWindow)
             }
         } else {
             App.app.checkIfShortcutsShouldBeDisabled(nil, app)
@@ -67,20 +73,9 @@ class AccessibilityEvents {
         }
     }
 
-    private static func handleEventWindowWithDebounceIfNecessary(_ type: String, _ pid: pid_t, _ element: AXUIElement) throws {
-        let wid = try element.cgWindowId()
-        guard wid != 0 || type == kAXUIElementDestroyedNotification else { return } // some bogus "windows" have wid 0
-        if type == kAXTitleChangedNotification || type == kAXWindowResizedNotification || type == kAXWindowMovedNotification {
-            AXUIElement.retryAxCallUntilTimeout(context: "(wid:\(wid) pid:\(pid))", debounceType: (type == kAXTitleChangedNotification ? .windowTitleChanged : .windowResizedOrMoved), pid: pid, wid: wid, callType: .updateWindow) {
-                try handleEventWindow(type, wid, pid, element)
-            }
-        } else {
-            try handleEventWindow(type, wid, pid, element)
-        }
-    }
-
     static func handleEventWindow(_ type: String, _ wid: CGWindowID, _ pid: pid_t, _ element: AXUIElement) throws {
-        guard wid != App.app.thumbnailsPanel.windowNumber else { return } // don't process events for the thumbnails panel
+        guard wid != 0 || type == kAXUIElementDestroyedNotification,
+              wid != App.app.thumbnailsPanel.windowNumber else { return } // don't process events for the thumbnails panel
         let level = wid.level()
         let a = try element.attributes([kAXTitleAttribute, kAXSubroleAttribute, kAXRoleAttribute, kAXSizeAttribute, kAXPositionAttribute, kAXFullscreenAttribute, kAXMinimizedAttribute])
         DispatchQueue.main.async {