我最近开始使用 Rust 进行编码,我很喜欢它。我正在一个项目上编码,我想“包装”C-API。在一种情况下,我必须在 Rust 中定义 C 可以调用的回调。我让bindgen 创建了回调。由于代码需要异步运行,因此我使用 tokio。
我想要实现的目标
我将 main 函数创建为 tokio::main。在主函数中,我创建了 2 个异步任务,一个监听 channel ,另一个触发 C-API 中的消息队列。如果消息可用,我想通过回调函数上的 channel 发送它们,这样我就可以接收有关我正在监听事件的任务的消息。稍后我想通过 SSE 或 GraphQL 订阅将这些消息发送给多个客户端。
我无法更改 C-Callbacks,因为它们需要可传递给 C-API,并且我必须使用回调,否则我不会收到消息。
我最新的方法看起来像这样简化了:
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)
}
}
}
问题:
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
我理解该消息以及为什么会发生这种情况,但我想不出解决方案。
我有一个使用 crossbeam channel 的工作示例,但我宁愿使用 tokio 的异步 channel ,所以我没有那么多依赖项,并且一切都是异步的。
工作示例:
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),
}
}
替代方案
另一种选择,我也没有开始工作,是使用某种本地函数或使用闭包。但我不确定这是否有效,即使是否有效。也许有人有想法。如果这样的东西可以工作,那就太好了,这样我就不必使用lazy_static(我不想在我的代码中使用全局/静态变量)
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();
}
这种方法的问题
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
如果有人能解决我的问题,那就太好了。如果这是一种全新的方法,那也很好。如果 Channels 或 tokio 或其他任何东西都不是正确的选择,那也没关系。主要是我用了tokio,因为一个crate我也在用tokio,所以我不需要有更多的依赖。
非常感谢您阅读到这里。
最佳答案
如果您对第一个示例进行以下更改,它应该可以工作:
- 将
tokio::sync::Mutex
替换为std::sync::Mutex
,这样您就不必在中使用try_lock
回调。 - 不要将接收者存储在互斥体中,仅将发送者存储在互斥体中。
- 在回调中,要么使用无界 channel ,要么确保在发送之前释放锁定。
- 使用
std::thread::spawn
在专用线程上运行阻塞 C 代码,而不是在tokio::spawn
中。 (why?)
为了不将接收器存储在互斥锁中,您可以这样做:
static ref BROADCAST_CONNECT: Mutex<Option<Sender<bool>>> = Mutex::new(None);
// in main
let (send, recv) = channel(128);
*BROADCAST_CONNECT.lock().unwrap() = Some(send);
如果您想要有界 channel ,可以先克隆 channel ,然后对锁调用 drop
,然后使用 blocking_send
发送来释放锁。对于无限制的 channel ,这并不重要,因为发送是即时的。
// in C callback
let lock = BROADCAST_CONNECT.lock().unwrap();
let send = lock.as_ref().clone();
drop(lock);
send.blocking_send(...);
关于asynchronous - RuSTLazy_static 和 tokio::sync::mpsc::tokio::select 中的 channel ,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/65452692/