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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Borrowing vs. Boxing in Async-heavy Code: How do you mentor juniors through lifetime hell?

We're porting our Python WebSocket service (10k msg/s) to Rust/Tokio and hit a recurring wall: juniors writing async fn process(&self) that fights the borrow checker when spawning tasks. Classic case:

struct Processor {
    cache: RefCell<HashMap<u64, Data>>, // 🤦
}

impl Processor {
    async fn handle_event(&self, event: Event) {
        let mut guard = self.cache.borrow_mut(); // Blocks entire struct
        // ...await point here = 💥
    }
}

The pain:

• Overusing Arc<Mutex<_>> kills throughput (contention up 300% in benchmarks)
• Box::pin + 'static lifetimes confuse those coming from GC langs
• Fear-driven clone() everywhere → memory bloat

Our stopgaps:

1. #![deny(clippy::await_holding_lock)]
2. Training sessions on Pin, Arc::clone discipline
3. Structured learning paths via platforms like CoderLegion for async fundamentals

Discussion points:
What's your threshold for unsafe when lifetimes fight back? (We drew line at 0.1% LOC)
How do you debug stuck futures without RUST_BACKTRACE=full crutches?
Are collaborative code reviews better than solo struggles for ownership mastery?
Could community learning resources help shorten the "Rust despair curve"?

(Production horror: Deadlock in our #[tokio::test] suite only triggered at 7k rps. Solution: tracing::instrument + tokio-console.)

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