EventLoopProxy is !Sync on macOS

[WilliamVenner]

I'm pretty sure CFRunLoopSourceSignal, CFRunLoopGetMain and CFRunLoopWakeUp are thread-safe on macOS.

std::sync::mpsc::Sender became Sync in Rust 1.72.0.

If we want to support older Rust versions, would it not be worth swapping std mpsc for crossbeam-channel in order to support sending user events from other threads?

If not a bug, then this is also a bit of an undocumented footgun. I didn't really expect EventLoopProxy to be !Sync, isn't the whole idea for sending events from other threads? Sure, I guess users can just wrap it in a Mutex, but that's introducing somewhat needlessly complicated platform-specific code downstream, and I don't think that's the intention.

[WilliamVenner]

Nevermind, I think this is intentional, and Rust 1.72.0 caused platform differences in winit that lead to EventLoopProxy becoming auto Sync on some platforms.