fn setup_control_flow_observers()

in src/platform_impl/ios/event_loop.rs [204:296]

• 74 lines of code
• 1 McCabe index (conditional complexity)

fn setup_control_flow_observers() {
    unsafe {
        // begin is queued with the highest priority to ensure it is processed before other observers
        extern "C" fn control_flow_begin_handler(
            _: CFRunLoopObserverRef,
            activity: CFRunLoopActivity,
            _: *mut c_void,
        ) {
            unsafe {
                #[allow(non_upper_case_globals)]
                match activity {
                    kCFRunLoopAfterWaiting => app_state::handle_wakeup_transition(),
                    kCFRunLoopEntry => unimplemented!(), // not expected to ever happen
                    _ => unreachable!(),
                }
            }
        }

        // Core Animation registers its `CFRunLoopObserver` that performs drawing operations in
        // `CA::Transaction::ensure_implicit` with a priority of `0x1e8480`. We set the main_end
        // priority to be 0, in order to send MainEventsCleared before RedrawRequested. This value was
        // chosen conservatively to guard against apple using different priorities for their redraw
        // observers in different OS's or on different devices. If it so happens that it's too
        // conservative, the main symptom would be non-redraw events coming in after `MainEventsCleared`.
        //
        // The value of `0x1e8480` was determined by inspecting stack traces and the associated
        // registers for every `CFRunLoopAddObserver` call on an iPad Air 2 running iOS 11.4.
        //
        // Also tested to be `0x1e8480` on iPhone 8, iOS 13 beta 4.
        extern "C" fn control_flow_main_end_handler(
            _: CFRunLoopObserverRef,
            activity: CFRunLoopActivity,
            _: *mut c_void,
        ) {
            unsafe {
                #[allow(non_upper_case_globals)]
                match activity {
                    kCFRunLoopBeforeWaiting => app_state::handle_main_events_cleared(),
                    kCFRunLoopExit => unimplemented!(), // not expected to ever happen
                    _ => unreachable!(),
                }
            }
        }

        // end is queued with the lowest priority to ensure it is processed after other observers
        extern "C" fn control_flow_end_handler(
            _: CFRunLoopObserverRef,
            activity: CFRunLoopActivity,
            _: *mut c_void,
        ) {
            unsafe {
                #[allow(non_upper_case_globals)]
                match activity {
                    kCFRunLoopBeforeWaiting => app_state::handle_events_cleared(),
                    kCFRunLoopExit => unimplemented!(), // not expected to ever happen
                    _ => unreachable!(),
                }
            }
        }

        let main_loop = CFRunLoopGetMain();

        let begin_observer = CFRunLoopObserverCreate(
            ptr::null_mut(),
            kCFRunLoopEntry | kCFRunLoopAfterWaiting,
            1, // repeat = true
            CFIndex::min_value(),
            control_flow_begin_handler,
            ptr::null_mut(),
        );
        CFRunLoopAddObserver(main_loop, begin_observer, kCFRunLoopDefaultMode);

        let main_end_observer = CFRunLoopObserverCreate(
            ptr::null_mut(),
            kCFRunLoopExit | kCFRunLoopBeforeWaiting,
            1, // repeat = true
            0, // see comment on `control_flow_main_end_handler`
            control_flow_main_end_handler,
            ptr::null_mut(),
        );
        CFRunLoopAddObserver(main_loop, main_end_observer, kCFRunLoopDefaultMode);

        let end_observer = CFRunLoopObserverCreate(
            ptr::null_mut(),
            kCFRunLoopExit | kCFRunLoopBeforeWaiting,
            1, // repeat = true
            CFIndex::max_value(),
            control_flow_end_handler,
            ptr::null_mut(),
        );
        CFRunLoopAddObserver(main_loop, end_observer, kCFRunLoopDefaultMode);
    }
}