fix high CPU usage #1481

src/api-wrappers/AXUIElement.swift

@@ -21,7 +21,7 @@ func retryAxCallUntilTimeout_(_ group: DispatchGroup?, _ timeoutInSeconds: Doubl
     } catch {
         let timePassedInSeconds = Double(DispatchTime.now().uptimeNanoseconds - startTime.uptimeNanoseconds) / 1_000_000_000
         if timePassedInSeconds < timeoutInSeconds {
-            BackgroundWork.axCallsQueue.asyncAfter(deadline: .now() + .milliseconds(10)) {
+            BackgroundWork.axCallsQueue.asyncAfter(deadline: .now() + .milliseconds(250)) {
                 retryAxCallUntilTimeout_(group, timeoutInSeconds, fn, startTime)
             }
         }

src/logic/Applications.swift

@@ -18,6 +18,7 @@ class Applications {
         addInitialRunningApplications()
         addInitialRunningApplicationsWindows()
         WorkspaceEvents.observeRunningApplications()
+        WorkspaceEvents.registerFrontAppChangeNote()
     }
 
     static func addInitialRunningApplications() {
@@ -104,7 +105,30 @@ class Applications {
     private static func isActualApplication(_ app: NSRunningApplication) -> Bool {
         // an app can start with .activationPolicy == .prohibited, then transition to != .prohibited later
         // an app can be both activationPolicy == .accessory and XPC (e.g. com.apple.dock.etci)
-        return (isNotXpc(app) || isAndroidEmulator(app)) && !app.processIdentifier.isZombie()
+        return (isNotXpc(app) || isAndroidEmulator(app)) && !app.processIdentifier.isZombie() && isAnWindowApplication(app)
+    }
+
+    private static func isAnWindowApplication(_ app: NSRunningApplication) -> Bool {
+        if (app.isActive) {
+            // Because we only add the application when we receive the didActivateApplicationNotification.
+            // So here is actually the handling for the case wasLaunchedBeforeAltTab=false. For applications where wasLaunchedBeforeAltTab=true, the majority of isActive is false.
+            // The reason for not using axUiElement.windows() here as a way to determine if it is a window application is that
+            // When we receive the didActivateApplicationNotification notification, the application may still be loading and axUiElement.windows() will throw an exception
+            // So we use isActive to determine if it is a window application, even if the application is not frontmost, isActive is still true at this time
+            return true;
+        } else {
+            do {
+                // For wasLaunchedBeforeAltTab=true, we assume that those apps are all launched, if they are programs with windows.
+                // Even if it has 0 windows at this point, axUiElement.windows() will not throw an exception. If they are programs without windows, then axUiElement.windows() will throw an exception.
+                // Here I consider there is an edge case where AltTab is starting up and this program has been loading, then it is possible that axUiElement.windows() will throw an exception.
+                // I'm not quite sure if this happens, but even if it does, then after restarting this application, AltTab captures its window without any problem. I think this happens rarely.
+                let axUiElement = AXUIElementCreateApplication(app.processIdentifier)
+                try axUiElement.windows()
+                return true
+            } catch {
+                return false
+            }
+        }
     }
 
     private static func isNotXpc(_ app: NSRunningApplication) -> Bool {

src/logic/events/WorkspaceEvents.swift

@@ -14,11 +14,30 @@ class WorkspaceEvents {
         let diff = Array(workspaceApps.symmetricDifference(previousValueOfRunningApps))
         if change.kind == .insertion {
             debugPrint("OS event", "apps launched", diff.map { ($0.processIdentifier, $0.bundleIdentifier) })
-            Applications.addRunningApplications(diff)
         } else if change.kind == .removal {
             debugPrint("OS event", "apps quit", diff.map { ($0.processIdentifier, $0.bundleIdentifier) })
             Applications.removeRunningApplications(diff)
+            previousValueOfRunningApps = workspaceApps
+        }
+    }
+
+    static func registerFrontAppChangeNote() {
+        NSWorkspace.shared.notificationCenter.addObserver(self, selector: #selector(receiveFrontAppChangeNote(_:)), name: NSWorkspace.didActivateApplicationNotification, object: nil)
+    }
+
+    // We add apps when we receive a didActivateApplicationNotification notification, not when we receive an apps launched, because any app will have an apps launched notification.
+    // But we are only interested in apps that have windows. We think that since an app can be activated, it must have a window, and subscribing to its window event makes sense and is likely to work, even if it requires multiple retries to subscribe.
+    // I'm not very sure if there is an edge case, but so far testing down the line has not revealed it.
+    // When we receive the didActivateApplicationNotification notification, NSRunningApplication.isActive=true, even if the app is not the frontmost window anymore.
+    // If we go to add the application when we receive the message of apps launched, at this time NSRunningApplication.isActive may be false, and try axUiElement.windows() may also throw an exception.
+    // For those background applications, we don't receive notifications of didActivateApplicationNotification until they have their own window. For example, those menu bar applications.
+    @objc static func receiveFrontAppChangeNote(_ notification: Notification) {
+        if let application = notification.userInfo?["NSWorkspaceApplicationKey"] as? NSRunningApplication {
+            debugPrint("OS event", "didActivateApplicationNotification", application.bundleIdentifier)
+            let workspaceApps = Set(NSWorkspace.shared.runningApplications)
+            let diff = Array(workspaceApps.symmetricDifference(previousValueOfRunningApps))
+            Applications.addRunningApplications(diff)
+            previousValueOfRunningApps = workspaceApps
         }
-        previousValueOfRunningApps = workspaceApps
     }
 }