perf: debounce screen/space events to minimize work

src/logic/events/ScreensEvents.swift

@@ -1,19 +1,52 @@
 import Cocoa
 
 class ScreensEvents {
+    static let debouncerScreenAndSpace = Debouncer(.main)
+
     static func observe() {
         NotificationCenter.default.addObserver(self, selector: #selector(handleEvent), name: NSApplication.didChangeScreenParametersNotification, object: nil)
     }
 
     @objc private static func handleEvent(_ notification: Notification) {
-        Logger.debug { notification.name.rawValue }
-        Spaces.refresh()
-        // a screen added or removed, or screen resolution change can mess up layout; we reset components
-        App.app.resetPreferencesDependentComponents()
-        // a screen added or removed can shuffle windows around Spaces; we refresh them
-        App.app.refreshOpenUi(Windows.list, .refreshUiAfterExternalEvent)
-        Logger.info { "screens:\(NSScreen.screens.map { ($0.uuid() ?? "nil" as CFString, $0.frame) })" }
-        Logger.info { "spaces:\(Spaces.screenSpacesMap)" }
-        Logger.info { "current space:\(Spaces.currentSpaceIndex) (id:\(Spaces.currentSpaceId))" }
+        // screen notifications often arrive in groups (e.g. 2 in a row in a short time)
+        // we debounce to minimize work
+        debouncerScreenAndSpace.debounce(.screenEvent) {
+            Logger.debug { notification.name.rawValue }
+            Spaces.refresh()
+            // a screen added or removed, or screen resolution change can mess up layout; we reset components
+            App.app.resetPreferencesDependentComponents()
+        }
     }
 }
+
+final class Debouncer {
+    private let queue: DispatchQueue
+    private var workItem: DispatchWorkItem?
+    private var contextsBlocks = [DebounceContext: () -> Void]()
+
+    init(_ queue: DispatchQueue) {
+        self.queue = queue
+    }
+
+    func debounce(_ context: DebounceContext, _ block: @escaping () -> Void) {
+        contextsBlocks[context] = block
+        workItem?.cancel()
+        let item = DispatchWorkItem(block: {
+            for block in self.contextsBlocks.values {
+                block()
+            }
+            // ScreensEvents: a screen added or removed can shuffle windows around Spaces; we refresh them
+            // SpacesEvents: if UI was kept open during Space transition, the Spaces may be obsolete; we refresh them
+            App.app.refreshOpenUi(Windows.list, .refreshUiAfterExternalEvent)
+            Logger.info { "screens:\(NSScreen.screens.map { ($0.uuid() ?? "nil" as CFString, $0.frame) })" }
+            Logger.info { "currentSpace:\(Spaces.currentSpaceIndex) (id:\(Spaces.currentSpaceId)) spaces:\(Spaces.screenSpacesMap)" }
+        })
+        workItem = item
+        queue.asyncAfter(deadline: .now() + humanPerceptionDelay, execute: item)
+    }
+}
+
+enum DebounceContext {
+    case spaceEvent
+    case screenEvent
+}

src/logic/events/SpacesEvents.swift

@@ -6,14 +6,13 @@ class SpacesEvents {
     }
 
     @objc private static func handleEvent(_ notification: Notification) {
-        Logger.debug { notification.name.rawValue }
-        // if UI was kept open during Space transition, the Spaces may be obsolete; we refresh them
-        App.app.refreshOpenUi(Windows.list, .refreshUiAfterExternalEvent)
-        Logger.info { "current space:\(Spaces.currentSpaceIndex) (id:\(Spaces.currentSpaceId))" }
-        // Workaround for Safari full-screen videos
-        // when full-screening a video, Safari spawns a second full-screen window called "Safari"
-        // this window doesn't emit resize/move events. It doesn't pass isActualWindow on creation. It's added on focusedWindowChanged
-        // for such cases, we refresh isFullscreen on Space change
-        Windows.updateIsFullscreenOnCurrentSpace()
+        ScreensEvents.debouncerScreenAndSpace.debounce(.spaceEvent) {
+            Logger.debug { notification.name.rawValue }
+            // Workaround for Safari full-screen videos
+            // when full-screening a video, Safari spawns a second full-screen window called "Safari"
+            // this window doesn't emit resize/move events. It doesn't pass isActualWindow on creation. It's added on focusedWindowChanged
+            // for such cases, we refresh isFullscreen on Space change
+            Windows.updateIsFullscreenOnCurrentSpace()
+        }
     }
 }