Rust

As someone who has tried doing multithreaded design with Arc/Mutex, this is a complete nightmare.

I myself often use channels. And pass owned data around.

I don't think anyone argues that Arc+interior-mutation is ideal. But it's the over-the-top language like "complete nightmare" that some may take issue with.

Note that I again make the distinction between Mutex, and all interior mutation primitives. Because Mutex is indeed a bad choice in many cases. and over-usage of it may indeed be a signal that we have a developer who's not comfortable with Rust's ownership/borrowing semantics.

You constantly get into deadlocks and performance is abysmal, because Mutex is serializing access (so it’s not really async or multithreaded any more).

• Same note about Mutex specifically as above.
• Avoiding deadlocks can definitely be a challenge, true. But I wouldn't say it's often an insurmountable one.
• What crate did you use for interior mutability, async-lock, tokio, parking_lot, or just std?