[OSX] Crash when moving OpenGL context to another thread

[syrel]

I can't seem to be able to move an OpenGL context to another thread on OSX.

Calling make_current() on a NotCurrent context (even splitted) from a non-main thread results in an illegal hardware instruction.

Any ideas?

Here is a modified window.rs example:

mod support;

use glutin::event::{Event, WindowEvent};
use glutin::event_loop::{ControlFlow, EventLoop};
use glutin::window::WindowBuilder;
use glutin::ContextBuilder;

use std::{thread, time};

fn main() {
    let el = EventLoop::new();
    let wb = WindowBuilder::new().with_title("A fantastic window!");

    let windowed_context =
        ContextBuilder::new().build_windowed(wb, &el).unwrap();

    thread::spawn(move || {
        thread::sleep(time::Duration::from_secs(1));
        let windowed_context =
            unsafe { windowed_context.make_current().unwrap() };

        println!(
            "Pixel format of the window's GL context: {:?}",
            windowed_context.get_pixel_format()
        );
    });

    el.run(move |event, _, control_flow| {
        println!("{:?}", event);
        *control_flow = ControlFlow::Wait;

        match event {
            Event::LoopDestroyed => return,
            Event::WindowEvent { event, .. } => match event {
                WindowEvent::CloseRequested => {
                    *control_flow = ControlFlow::Exit
                }
                _ => (),
            },
            _ => (),
        }
    });
}

[syrel]

It appears to crash during NSOpenGLContext update being called from a non-ui thread.
macOS Catalina 10.15.5 Beta (19F62f)

Process 5385 stopped
* thread #8, stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
    frame #0: 0x00007fff32709c3d AppKit`-[NSOpenGLContext update] + 525
AppKit`-[NSOpenGLContext update]:
->  0x7fff32709c3d <+525>: ud2    
    0x7fff32709c3f <+527>: movq   %rax, %r14
    0x7fff32709c42 <+530>: jmp    0x7fff32709c4b            ; <+539>
    0x7fff32709c44 <+532>: movq   %rax, %r14

[kchibisov]

I'd need to retest it with macOS, but I think the issue should be there after #1435. Solving it should be possibly though, given that we can use libdispatch to transfer update.

[kchibisov]

I've looked in apple docs for that and it seems that it's fine https://developer.apple.com/documentation/appkit/nsopenglcontext/1436135-update?language=objc

[madsmtm]

We discussed this on Matrix, I could not reproduce the original issue on my machine (running macOS 10.14.6), neither on v0.24.1 nor v0.30.0-beta.1.

Even with the following diff (which is not safe, but for illustration) I did not get the crash:

diff --git a/glutin_examples/examples/window.rs b/glutin_examples/examples/window.rs
index 0b09a8a..0b1e596 100644
--- a/glutin_examples/examples/window.rs
+++ b/glutin_examples/examples/window.rs
@@ -66,17 +66,22 @@ fn main() {
         match event {
             Event::WindowEvent { event, .. } => match event {
                 WindowEvent::Resized(size) => {
-                    if size.width != 0 && size.height != 0 {
-                        // Some platforms like EGL require resizing GL surface to update the size
-                        // Notable platforms here are Wayland and macOS, other don't require it
-                        // and the function is no-op, but it's wise to resize it for portability
-                        // reasons.
-                        gl_window.surface.resize(
-                            &gl_context,
-                            NonZeroU32::new(size.width).unwrap(),
-                            NonZeroU32::new(size.height).unwrap(),
-                        );
-                    }
+                    use glutin::context::{AsRawContext, RawContext};
+                    // `objc = "0.2.7"`
+                    use objc::{msg_send, sel, sel_impl};
+
+                    dbg!(size);
+                    struct ThreadSafe<T>(T);
+                    unsafe impl<T> Send for ThreadSafe<T> {}
+                    let raw = ThreadSafe(gl_context.raw_context());
+                    std::thread::spawn(|| {
+                        let raw = raw;
+                        let raw: *const objc::runtime::Object = match raw.0 {
+                            RawContext::Cgl(x) => x.cast(),
+                        };
+
+                        let _: () = unsafe { msg_send![raw, update] };
+                    });
                 },
                 WindowEvent::CloseRequested => {
                     *control_flow = ControlFlow::Exit;