perf: prevent random freezes of the ui (#563)

timers were on the main thread, creating indeterministic freezes

src/logic/BackgroundWork.swift

@@ -8,6 +8,7 @@ class BackgroundWork {
     static var crashReportsQueue: DispatchQueue!
     static var accessibilityEventsThread: BackgroundThreadWithRunLoop!
     static var mouseEventsThread: BackgroundThreadWithRunLoop!
+    static var systemPermissionsThread: BackgroundThreadWithRunLoop!
 
     // we cap concurrent tasks to .processorCount to avoid thread explosion on the .global queue
     static let globalSemaphore = DispatchSemaphore(value: ProcessInfo.processInfo.processorCount)
@@ -21,6 +22,10 @@ class BackgroundWork {
         accessibilityEventsThread = BackgroundThreadWithRunLoop("accessibilityEventsThread", .userInteractive)
         mouseEventsThread = BackgroundThreadWithRunLoop("mouseEventsThread", .userInteractive)
     }
+
+    static func startSystemPermissionThread() {
+        systemPermissionsThread = BackgroundThreadWithRunLoop("systemPermissionsThread", .utility)
+    }
 }
 
 extension DispatchQueue {

src/logic/SystemPermissions.swift

@@ -42,12 +42,13 @@ class SystemPermissions {
     }
 
     static func observePermissionsPostStartup() {
-        timer = Timer.scheduledTimer(withTimeInterval: 5, repeats: true, block: { _ in
+        timer = Timer(timeInterval: 5, repeats: true, block: { _ in
             if !(accessibilityIsGranted() && screenRecordingIsGranted()) {
                 App.app.restart()
             }
         })
         timer.tolerance = 4.9
+        CFRunLoopAddTimer(BackgroundWork.systemPermissionsThread.runLoop, timer, .defaultMode)
     }
 
     static func observePermissionsPreStartup(_ startupBlock: @escaping () -> Void) {
@@ -55,23 +56,26 @@ class SystemPermissions {
             // this call triggers the permission prompt, however it's the only way to force the app to be listed with a checkbox
             SLSRequestScreenCaptureAccess()
         }
-        timer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true, block: { _ in
+        timer = Timer(timeInterval: 0.1, repeats: true) { _ in
             let accessibility = accessibilityIsGranted()
             let screenRecording = screenRecordingIsGranted()
-            if accessibility && screenRecording {
-                permissionsWindow.close()
-                timer.invalidate()
-                startupBlock()
-            } else {
-                if accessibility != permissionsWindow.accessibilityView.isPermissionGranted {
-                    permissionsWindow.accessibilityView.updatePermissionStatus(accessibility)
-                }
-                if #available(OSX 10.15, *), screenRecording != permissionsWindow.screenRecordingView.isPermissionGranted {
-                    permissionsWindow.screenRecordingView.updatePermissionStatus(screenRecording)
+            DispatchQueue.main.async {
+                if accessibility && screenRecording {
+                    permissionsWindow.close()
+                    timer.invalidate()
+                    startupBlock()
+                } else {
+                    if accessibility != permissionsWindow.accessibilityView.isPermissionGranted {
+                        permissionsWindow.accessibilityView.updatePermissionStatus(accessibility)
+                    }
+                    if #available(OSX 10.15, *), screenRecording != permissionsWindow.screenRecordingView.isPermissionGranted {
+                        permissionsWindow.screenRecordingView.updatePermissionStatus(screenRecording)
+                    }
                 }
             }
-        })
+        }
         timer.tolerance = 0.09
+        CFRunLoopAddTimer(BackgroundWork.systemPermissionsThread.runLoop, timer, .defaultMode)
     }
 
     static func ensurePermissionsAreGranted(_ continueAppStartup: @escaping () -> Void) {

src/ui/App.swift

@@ -41,6 +41,7 @@ class App: AppCenterApplication, NSApplicationDelegate {
         PFMoveToApplicationsFolderIfNecessary()
         #endif
         AXUIElement.setGlobalTimeout()
+        BackgroundWork.startSystemPermissionThread()
         SystemPermissions.ensurePermissionsAreGranted { [weak self] in
             guard let self = self else { return }
             BackgroundWork.start()

src/ui/permission-window/PermissionsWindow.swift

@@ -4,8 +4,8 @@ class PermissionsWindow: NSWindow, NSWindowDelegate {
     var accessibilityView: PermissionView!
     var screenRecordingView: PermissionView!
 
-    override init(contentRect: NSRect, styleMask style: StyleMask, backing backingStoreType: BackingStoreType, defer flag: Bool) {
-        super.init(contentRect: .zero, styleMask: style, backing: backingStoreType, defer: flag)
+    convenience init() {
+        self.init(contentRect: .zero, styleMask: [.titled, .miniaturizable, .closable], backing: .buffered, defer: false)
         delegate = self
         setupWindow()
         setupView()