async
2025-06-12
julyfunlang-modelnotes技术学习大致概念：[80%-sure] 以 Rust 为例，运行到 func().await 时 (func 为 async fn)func() 内部代码完全交由 async runtime 处理func() 内部通常有等待IO/GPU/定时器的异步部分。这些部分不由 CPU 负责运算，不应该让 CPU 干等着，所以才写成异步函数.如果 func() 内部全是同步代码，没有 .await 或手动挂起点，写成异步（async fn）没有实际意义它是不会挂起的，会同步执行完毕。轮询poll 调用次数不是固定的，取决于任务的完成时机和外部事件。Rustasync fn my_async(x: u32) -> u32 {
let a = x + 1;
a * 2
}
let fut = my_async(10);
fut.await; // 开始轮询编译器生成的大致逻辑:enum MyAsyncState {
Start { x: u32 },
Done,
}
struct MyAsyncFuture {
state: MyAsyncState,
}
impl Future for MyAsyncFuture {
type Output = u32;
fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<u32> {
match self.state {
MyAsyncState::Start { x } => {
let a = x + 1;
let result = a * 2;
self.state = MyAsyncState::Done;
Poll::Ready(result)
},
MyAsyncState::Done => {
panic!("polled after completion");
}
}
}
}另一个例子：async fn my_async(x: u32) -> u32 {
let a = x + 1;
tokio::time::sleep(Duration::from_secs(3)).await;
a * 2
}enum MyAsyncState {
Start { x: u32 },
Waiting { a: u32, sleep_future: Sleep },
Done,
}
impl Future for MyAsyncFuture {
type Output = u32;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<u32> {
loop {
match self.state {
MyAsyncState::Start { x } => {
let a = x + 1;
let sleep_future = tokio::time::sleep(Duration::from_secs(3));
self.state = MyAsyncState::Waiting { a, sleep_future };
},
MyAsyncState::Waiting { a, ref mut sleep_future } => {
match Pin::new(sleep_future).poll(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(_) => {
let result = a * 2;
self.state = MyAsyncState::Done;
return Poll::Ready(result);
}
}
},
MyAsyncState::Done => {
panic!("polled after completion");
}
}
}
}