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::thread;

    use cocoa::appkit::NSApplication;

    unsafe {
        let app = cocoa::appkit::NSApp();
        let t = thread::spawn(|| {
            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()
    }
}