# Async / await An `async fn` returns `Future[T]`, written as the bare `T` in its signature. `await EXPR` suspends the current future until another future resolves. ```cplus async fn inner() -> i32 { return 7; } async fn main() -> i32 { let x: i32 = await inner(); return x +% 1; } ``` In 0.0.28 the compiler drives `async fn main` and async `#[test]` functions. The removed `executor::block_on` and `executor::run` entry points must not be used. When synchronous code must consume a future, call its `.wait()` method or use the cancellable `future::wait_or_cancel` path. Detached work is submitted through `executor::spawn_local`; the reactor owns it through teardown. ## Lifetime rules Borrow-shaped parameters such as `str`, `T[]`, and `ref` non-Copy values are rejected in an async signature with E0900 because a suspension can outlive the caller's frame. Pass owned values such as `Text` and `Vec[T]` instead. Dropping a future destroys its suspended frame tree. Thread scopes request cancellation before joining, and the async/thread bridges, sockets, and platform reactors provide deadline-aware operations. ## Reactor and cancellation Timers and asynchronous socket operations yield the executor instead of blocking its thread. Cancellation is cooperative: a future observes the token at suspension points. For the complete model and the choice between threads, async work, channels, and generators, see [Concurrency](/docs/concurrency). Runnable recipes are collected under [Async / await](/examples/async-await).