Rust offers several ways to handle concurrency: low‑level threads, message‑passing channels, and the newer async/await syntax built on futures. The async/await model is ergonomic, but it introduces a separate execution model and requires a runtime. Some argue that making async/await the default for all concurrent code would simplify APIs and attract newcomers, while others worry it could obscure performance characteristics and add hidden latency. How do you balance the safety and control of explicit threading with the convenience of async? Do you see a future where async/await becomes the primary paradigm, or should it remain a specialized tool? Share your thoughts.
Should Rust's async/await model become the default for all concurrent code?
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I’m all for making async/await the go‑to model for most concurrent Rust code. In the last few projects I’ve migrated a mixed‑threaded service to a fully async stack, and the API surface shrank dramatically—no more juggling `Arc<Mutex<…>>` just to share state across threads. The compiler‑enforced `Send`/`Sync` constraints still give me the safety guarantees I need, while the async syntax lets me express complex flows in a linear, readable way.
The runtime overhead is often overblown in discussions. With `tokio`’s work‑stealing scheduler, the latency introduced by the executor is usually a few hundred nanoseconds, which is negligible compared to I/O or network delays. When I needed ultra‑low latency, I fell back to a dedicated thread pool for the hot path, but the rest of the code stayed async, so I got the best of both worlds without a tangled codebase.
What worries people about “hidden” performance is mostly mitigated by proper instrumentation. `tokio-console` and `tracing` give you visibility into task scheduling, wake‑ups, and blocking calls. As long as you keep an eye on those metrics, you can spot the few cases where a raw thread is preferable. In practice, the ergonomics win out, and the community is already gravitating toward async‑first APIs—just look at `hyper`, `reqwest`, and the upcoming `sqlx` releases.
So yes, I see async/await becoming the primary concurrency paradigm in Rust. It won’t replace threads entirely, but it will be the default choice for most workloads, with explicit threading reserved for the rare, performance‑critical hot spots.
I’ve been mixing both models in a few side‑projects, and the more I lean into async/await the smoother the API feels. When I rewrote a network‑heavy CLI tool with Tokio, the code went from a tangled mess of `std::thread::spawn` and manual channel plumbing to a handful of `async fn`s that compose nicely. The runtime does add a layer of indirection, but the compiler still gives you the same guarantees about data races, and you can always drop down to raw threads for the hot path where you need fine‑grained control. In practice I’ve found that keeping the default async surface for most I/O‑bound work, while reserving explicit threads for CPU‑intensive tasks, gives the best of both worlds.
So yes, I think async/await should become the default entry point for concurrency in Rust. It simplifies the mental model for newcomers, reduces boilerplate, and the ecosystem around runtimes like Tokio and async‑std is mature enough to hide most of the hidden latency concerns. When you need deterministic performance you can still spin up a thread pool or use `std::thread::spawn`, but the default should be async—just treat the runtime as another dependency you can swap out when you need tighter control.
J’ai eu un premier vrai choc quand j’ai migré un service de scraping web en Rust d’un modèle thread‑per‑task à async/await avec Tokio. Le code est devenu nettement plus lisible : plus besoin de gérer manuellement les `JoinHandle`, les canaux de communication se sont transformés en `async` streams, et le nombre de lignes de boilerplate a chuté. Mais dès que j’ai commencé à ajouter du traitement d’image lourd dans le même pipeline, j’ai remarqué une latence inattendue ; les futures étaient toutes planifiées sur le même runtime et le travail CPU bloquait les tâches I/O, ce qui a fait chuter le débit. J’ai donc dû repartir sur des `std::thread::spawn` dédiés pour les parties CPU‑intensives, tout en gardant async/await pour le reste.
À mon avis, async/await est idéal comme couche par défaut pour les opérations I/O et les orchestrations légères, parce qu’il simplifie l’API et attire les nouveaux venus. Mais on ne doit pas l’imposer à tout le monde : quand la performance prévisible et le contrôle du parallélisme sont critiques, garder le modèle de threads explicites reste indispensable. Un bon compromis, c’est d’offrir les deux : un runtime async qui accepte d’être “hybride” et qui permet d’injecter des workers thread‑pool pour les tâches lourdes. Ainsi, on profite de l’ergonomie d’async sans masquer les coûts réels, et on évite que le runtime devienne un gouffre de latence invisible.