gstreamer-rs/examples/src/examples-common.rs

/// macOS has a specific requirement that there must be a run loop running on the main thread in
/// order to open windows and use OpenGL, and that the global NSApplication instance must be
/// initialized.

/// On macOS this launches the callback function on a thread.
/// On other platforms it's just executed immediately.
#[cfg(not(target_os = "macos"))]
pub fn run<T, F: FnOnce() -> T + Send + 'static>(main: F) -> T
where
    T: Send + 'static,
{
    main()
}

#[cfg(target_os = "macos")]
pub fn run<T, F: FnOnce() -> T + Send + 'static>(main: F) -> T
where
    T: Send + 'static,
{
    use std::{
        ffi::c_void,
        sync::mpsc::{channel, Sender},
        thread,
    };

    use cocoa::{
        appkit::{NSApplication, NSWindow},
        base::id,
        delegate,
    };
    use objc::{
        class, msg_send,
        runtime::{Object, Sel},
        sel, sel_impl,
    };

    unsafe {
        let app = cocoa::appkit::NSApp();
        let (send, recv) = channel::<()>();

        extern "C" fn on_finish_launching(this: &Object, _cmd: Sel, _notification: id) {
            let send = unsafe {
                let send_pointer = *this.get_ivar::<*const c_void>("send");
                let boxed = Box::from_raw(send_pointer as *mut Sender<()>);
                *boxed
            };
            send.send(()).unwrap();
        }

        let delegate = delegate!("AppDelegate", {
            app: id = app,
            send: *const c_void = Box::into_raw(Box::new(send)) as *const c_void,
            (applicationDidFinishLaunching:) => on_finish_launching as extern fn(&Object, Sel, id)
        });
        app.setDelegate_(delegate);

        let t = thread::spawn(move || {
            // Wait for the NSApp to launch to avoid possibly calling stop_() too early
            recv.recv().unwrap();

            let res = main();

            let app = cocoa::appkit::NSApp();
            app.stop_(cocoa::base::nil);

            // Stopping the event loop requires an actual event
            let event = cocoa::appkit::NSEvent::otherEventWithType_location_modifierFlags_timestamp_windowNumber_context_subtype_data1_data2_(
                cocoa::base::nil,
                cocoa::appkit::NSEventType::NSApplicationDefined,
                cocoa::foundation::NSPoint { x: 0.0, y: 0.0 },
                cocoa::appkit::NSEventModifierFlags::empty(),
                0.0,
                0,
                cocoa::base::nil,
                cocoa::appkit::NSEventSubtype::NSApplicationActivatedEventType,
                0,
                0,
            );
            app.postEvent_atStart_(event, cocoa::base::YES);

            res
        });

        app.run();

        t.join().unwrap()
    }
}