11-concurrency.md

+++ title = "11. Concurrency (Async/Await)" weight = 11 +++

11. Concurrency (Async/Await)

Zen C uses a stackless coroutine model for async/await -- no thread pool, no pthread dependency. This means async functions are transformed at compile time into state machines, not into threads.

Syntax

Declare an async function with async fn and await its result with the await keyword:

async fn fetch_data() -> string {
    return "Data";
}

fn main() {
    let result = await fetch_data();
}

{% alert(type="note") %} Unlike thread-based models, Zen C's await is a blocking poll loop that runs the entire async function to completion. This is intentional -- it makes the control flow predictable and eliminates the need for a runtime executor or thread pool. {% end %}

How it works

An async fn is transformed by the compiler into a state machine. Each await point becomes a state transition. The resulting Future struct holds the state, parameters, and sub-futures for awaited calls.

Sequential pattern

async fn task(n: int) -> int {
    return n * 2;
}

fn main() {
    let a = await task(5);
    let b = await task(a);
}