rust异步编程详细讲解

// wake 函数 reactor发现状态是ready 通知executor 函数
trait SimpleFuture {
    type Output;
    fn poll(&mut self, wake: fn()) -> Poll<Self::Output>;
    // fn poll(&mut self, wake: u32) -> Poll<Self::Output>;
}
enum Poll<T> {
    Ready(T),
    Pending,
}
future 返回的是Poll枚举 , 状态有Ready ,pending 状态
executor 调用 Future 任务，Ready 执行完成， pending 阻塞 执行其他任务
reactor 检查任务是否变成 ready

use std::thread;
use std::time::Duration;
trait SimpleFuture {
    type Output;
    // fn poll(&mut self, wake: fn()) -> Poll<Self::Output>;
    fn poll(&mut self, wake: u32) -> Poll<Self::Output>;
}
enum Poll<T> {
    Ready(T),
    Pending,
}
// 自定义循环技术
struct MySleeper {
    polls: u64,
    wake: u32, // 简化使用整数 替换函数
}
impl MySleeper {
    fn new(wake: u32) -> Self {
        MySleeper {
            polls: 0,
            wake: wake,
        }
    }
}
static mut FINISHED: bool = false;
impl SimpleFuture for MySleeper {
    type Output = ();
    fn poll(&mut self, wake: u32) -> Poll<Self::Output> {
        // 简化编程 使用unsafe 使用外部的变量
        unsafe {
            if FINISHED {
                Poll::Ready(())
            } else {
                self.wake = wake;
                self.polls += 1;
                println!("polls = {}", self.polls);
                Poll::Pending
            }
        }
    }
}
// 定义自定义Reactor
struct MyReactor {
    wake: u32,
    // 通知exector
    handle: Option<thread::JoinHandle<()>>, // 线程句柄
}
impl MyReactor {
    fn new() -> Self {
        MyReactor {
            wake: 0,
            handle: None,
        }
    }
    // 知道哪个wake 通知具体函数
    fn add_wake(&mut self, wake: u32) {
        self.wake = wake;
    }
    // check status
    fn check_status(&mut self) {
        if self.handle.is_none() {
            let wake = self.wake;
            // 模拟 通过死循环进行监控状态
            let handle = thread::spawn(|| loop {
                thread::sleep(Duration::from_secs(5));
                unsafe {
                    //模拟future就绪，然后调用wake
                    FINISHED = true;
                }
            });
            self.handle = Some(handle);
        }
    }
}
struct MyExecutor;
impl MyExecutor {
    fn block_on<F: SimpleFuture>(mut myfuture: F, wake: u32) {
        //阻塞执行future
        loop {
            match myfuture.poll(wake) {
                Poll::Ready(_) => {
                    println!("my future is ok");
                    break;
                }
                Poll::Pending => unsafe {
                    while !FINISHED {
                        // 循环 每隔一秒钟检测一下
                        thread::sleep(Duration::from_secs(1));
                    }
                }
            }
        }
    }
}
fn main() {
    let mut reactor = MyReactor::new();
    let sleeper = MySleeper::new(5);
    let wake = sleeper.wake;
    reactor.add_wake(wake);
    reactor.check_status();
    MyExecutor::block_on(sleeper, wake);
}

 async fn hello() {
     println!("hello");
 }
等价于下面函数
fn hello() -> impl Future<Output=()> {
    async {
        println!("hello");
    }
}

 pub trait Future {
     type Output;
    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
 }
// Pin 可以创建不可移动Future，通过不可移动对象在他们字段中存储指针
struct MyFut {
	a: i32,
	ptr: *const i32, // 指针指向字段a 所在的内存首地址
}

use std::future::Future;
fn my_function() -> impl Future<Output  = u8> {
	let closure = async |x: u8| {
		x
	};
	
	closure(5)
}
闭包在稳定版本还不支持，后续的版本中会支持 异步闭包
##### async lifetime 
```rust
这个函数的生命周期
// fn foo_expand(x: &'a u8) -> impl Future<Output = u8> + 'a {
//     async {
//         *x
//     }
// }
async fn foo(x: & u8) -> u8 {
    *x
}
// async 函数返回一个Future的对象
 fn good() -> impl Future<Output = u8>{
 // 异步代码块中，定义 变量后 调用foo_expand async 函数后进行await
     async {
     // x 修饰后 x 的生命周期有多长 就有多长
        let x = 5;
        foo_expand(&x).await
   }
}