Tokio：：Select中的Rust lazy_static和Tokio：：Sync：：mpsc：：Channel

Question

我将main函数创建为tokio：：main。在main函数中，我创建了两个异步任务，一个侦听通道，另一个触发C-API中的消息队列。如果消息可用，我希望通过回调函数上的通道发送它们，这样我就可以接收任务上的消息，在那里我正在监听事件。稍后，我希望通过SSE或GraphQL订阅将这些消息发送给几个客户机。

我不能更改C回调，因为它们需要被C-API通过，我必须使用回调，否则我不会得到消息。

我最新的方法看起来很简单：

use lazy_static::lazy_static;
use tokio::sync::{
    mpsc::{channel, Receiver, Sender},
    Mutex,
};
use bindgen::{notify_connect, notify_connectionstate};

lazy_static! {
    static ref BROADCAST_CONNECT: Mutex<(Sender<bool>, Receiver<bool>)> = Mutex::new(channel(128));
    static ref BROADCAST_CONNECTIONSTATE: Mutex<(Sender<u32>, Receiver<u32>)> = Mutex::new(channel(128));
}

#[tokio::main]
async fn main() {    
    unsafe { notify_connect(Some(_notify_connect)) } // pass the callback function to the C-API
    unsafe { notify_connectionstate(Some(_notify_connectionstate)) } // pass the callback function to the C-API

    tokio::spawn(async move { // wait for a channel to have a message
        loop {
            tokio::select! {
                // wating for a channel to receive a message
                Some(msg) = BROADCAST_CONNECT.lock().await.1.recv() => println!("{}", msg),
                Some(msg) = BROADCAST_CONNECTIONSTATE.lock().await.1.recv() => println!("{}", msg),
            }
        }
    });

    let handle2 = tokio::spawn(async move {
        loop {
            unsafe {
                message_queue_in_c(
                    some_handle,
                    true,
                    Duration::milliseconds(100).num_microseconds().unwrap(),
                )
            }
        }
    });

    handle.await.unwrap();
    habdle2.await.unwrap();
}

// the callback function that gets called from the C-API
unsafe extern "C" fn _notify_connect(is_connected: bool) {
    // C-API is not async, so use synchronous lock
    match BROADCAST_CONNECT.try_lock() {
        Ok(value) => match value.0.blocking_send(is_connected) {
            Ok(_) => {}
            Err(e) => {
                eprintln!("{}", e)
            }
        },
        Err(e) => {
            eprintln!("{}", e)
        }
    }
}

unsafe extern "C" fn _notify_connectionstate(connectionstate: u32) {
    match BROADCAST_CONNECTIONSTATE.try_lock() {
        Ok(value) => match value.0.blocking_send(connectionstate) {
            Ok(_) => {}
            Err(e) => {
                eprintln!("{}", e)
            }
        },
        Err(e) => {
            eprintln!("{}", e)
        }
    }
}

error[E0716]: temporary value dropped while borrowed
  --> src/main.rs:37:29
   |
35 | /             tokio::select! {
36 | |                 Some(msg) = BROADCAST_CONNECT.lock().await.1.recv() => println!("{}", msg),
37 | |                 Some(msg) = BROADCAST_CONNECTIONSTATE.lock().await.1.recv() => println!("{}", msg),
   | |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
38 | |             }
   | |             -
   | |             |
   | |_____________temporary value is freed at the end of this statement
   |               borrow later captured here by closure
   |
   = note: consider using a `let` binding to create a longer lived value

use lazy_static::lazy_static;
use crossbeam::{
    channel::{bounded, Receiver, Sender},
    select,
};
use bindgen::{notify_connect, notify_connectionstate};

lazy_static! {
    static ref BROADCAST_CONNECT: (Sender<bool>, Receiver<bool>) = bounded(128);
    static ref BROADCAST_CONNECTIONSTATE: (Sender<u32>, Receiver<u32>) = bounded(128);
}

#[tokio::main]
async fn main() {    
    unsafe { notify_connect(Some(_notify_connect)) } // pass the callback function to the C-API
    unsafe { notify_connectionstate(Some(_notify_connectionstate)) } // pass the callback function to the C-API

    let handle1 = tokio::spawn(async move {
        loop {
            select! {
                recv(&BROADCAST_CONNECT.1) -> msg => println!("is_connected: {:?}", msg.unwrap()),
                recv(&BROADCAST_CONNECTIONSTATE.1) -> msg => println!("connectionstate: {:?}", msg.unwrap()),
            }
        }
    });

    let handle2 = tokio::spawn(async move {
        loop {
            unsafe {
                message_queue_in_c(
                    some_handle,
                    true,
                    Duration::milliseconds(100).num_microseconds().unwrap(),
                )
            }
        }
    });

    handle.await.unwrap();
    handle2.await.unwrap();
}

// the callback function thats gets called from the C-API
unsafe extern "C" fn _notify_connect(is_connected: bool) {
    match &BROADCAST_CONNECT.0.send(is_connected) {
        Ok(_) => {}
        Err(e) => eprintln!("{}", e),
    };
}

unsafe extern "C" fn _notify_connectionstate(connectionstate: u32) {
    match BROADCAST_CONNECTIONSTATE.0.send(connectionstate) {
        Ok(_) => {}
        Err(e) => eprintln!("{}", e),
    }
}

use tokio::sync::{
    mpsc::{channel, Receiver, Sender},
    Mutex,
};
use bindgen::{notify_connect, notify_connectionstate};

#[tokio::main]
async fn main() {
    let app = app::App::new();

    let mut broadcast_connect = channel::<bool>(128);
    let mut broadcast_connectionstate = channel::<bool>(128);

    let notify_connect = {
        unsafe extern "C" fn _notify_connect(is_connected: bool) {
            match broadcast_connect.0.blocking_send(is_connected) {
                Ok(_) => {}
                Err(e) => {
                    eprintln!("{}", e)
                }
            }
        }
    };

    let notify_connectionstate = {
        unsafe extern "C" fn _notify_connectionstate(connectionstate: u32) {
            match broadcast_connectionstate.0.blocking_send(connectionstate) {
                Ok(_) => {}
                Err(e) => {
                    eprintln!("{}", e)
                }
            }
        }
    };

    unsafe { notify_connect(Some(notify_connect)) } // pass the callback function to the C-API
    unsafe { notify_connectionstate(Some(notify_connectionstate)) } // pass the callback function to the C-API

    let handle = tokio::spawn(async move {
        loop {
            tokio::select! {
                Some(msg) = broadcast_connect.1.recv() => println!("{}", msg),
                Some(msg) = broadcast_connectionstate.1.recv() => println!("{}", msg),
            }
        }
    });

    let handle2 = tokio::spawn(async move {
        loop {
            unsafe {
                message_queue_in_c(
                    some_handle,
                    true,
                    Duration::milliseconds(100).num_microseconds().unwrap(),
                )
            }
        }
    });

    handle.await.unwrap();
    handle2.await.unwrap();
}

can't capture dynamic environment in a fn item
  --> src/main.rs:47:19
   |
47 |             match broadcast_connectionstate.0.blocking_send(connectionstate) {
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: use the `|| { ... }` closure form instead

已经谢谢你了，一直读到这里。

Answer 1

如果对第一个示例进行以下更改，它应该可以工作：

1. 用std::sync::mutex替换tokio::sync::mutex，这样就不必在回调中使用try_lock。
2. 不要将接收方存储在互斥体中，只存储发送方。
3. 在回调中，要么使用无界通道，要么确保在发送之前释放锁。
4. 在使用std::thread::spawn而不是在tokio::spawn的专用线程上运行阻塞C代码。（为什么？）

若要不将接收方存储在互斥体中，可以执行以下操作：

static ref BROADCAST_CONNECT: Mutex<Option<Sender<bool>>> = Mutex::new(None);

// in main
let (send, recv) = channel(128);
*BROADCAST_CONNECT.lock().unwrap() = Some(send);

// in C callback
let lock = BROADCAST_CONNECT.lock().unwrap();
let send = lock.as_ref().clone();
drop(lock);
send.blocking_send(...);