Rust concurrency: the single-writer principle

Article note: Single-Writer (or "Owner Writes") is _the_ way for doing hardware description language work, and usually the least-awful way to do most parallel programming. We've known that for _at least_ a decade, but software people hate to hear it because it means you have to do actual mental work instead of grunt programming to solve problems. It's really clear why you don't fuck around with contention when you're thinking in terms of "I'm going to have to drive this D flipflop with two different wires, so I need an extra layer of arbitration logic, so I did this wrong."