Rust异步流过滤亮度设备的生命周期问题求解

我需要编写一个Rust函数获取亮度设备流，当用户指定设备名称时，根据异步获取的设备名称对流进行过滤。已将设备名称集合包装为Arc<HashSet<String>>以保证生命周期，但仍出现生命周期错误。

相关代码 #

use std::{sync::Arc, collections::HashSet};
use futures::{stream::BoxStream, StreamExt,TryStreamExt};
use brightness::{Brightness, BrightnessDevice};

fn get_devices<'a>(device_names: Arc<HashSet<String>>) -> BoxStream<'a, Result<BrightnessDevice, brightness::Error>> {
    if device_names.is_empty() {
        brightness::brightness_devices().boxed()
    } else {
        brightness::brightness_devices()
            .try_filter(move |device| {
                let device_names_clone = device_names.clone();
                async move {
                    let devname: Result<String, brightness::Error> = device.device_name().await;
                    devname.is_ok_and(|devname| device_names_clone.contains(&devname)) // bool
            }})
            .boxed()
    }
}

错误信息 #

error: lifetime may not live long enough
  --> src\funcs\mod.rs:55:21
   |
53 |                   .try_filter(move |device| {
   |                                     ------- return type of closure `[async block@src\funcs\mod.rs:55:21: 58:18]` contains a lifetime `'2`
   |                                     |
   |                                     has type `&'1 brightness::BrightnessDevice`
54 |                       let device_names_clone = device_names.clone();
55 | /                     async move {
56 | |                         let devname: Result<String, brightness::Error> = device.device_name().await;
57 | |                         devname.is_ok_and(|devname| device_names_clone.contains(&devname)) // bool
58 | |                 }})
   | |_________________^ returning this value requires that `'1` must outlive `'2`

brightness crate 相关函数定义 #

// brightness::r#async
pub fn brightness_devices() -> impl Stream<Item = Result<BrightnessDevice, Error>>

// brightness::r#async::BrightnessDevice
fn device_name<'life0, 'async_trait>(&'life0 self) -> ::core::pin::Pin<Box<dyn ::core::future::Future<Output = Result<String, Error>> + ::core::marker::Send + 'async_trait>>
where
    'life0: 'async_trait,
    Self: 'async_trait

解决方案 #

问题根源 #

try_filter的闭包参数是对BrightnessDevice的引用，而异步block会捕获这个引用并持有它直到device_name()的future完成。但编译器无法保证该引用的生命周期足够长——流中的设备所有权属于流本身，引用的生命周期仅局限于闭包调用阶段，而异步block可能在闭包返回后才执行，这会导致引用悬空的风险，因此触发生命周期错误。

修复代码 #

改用try_filter_map替代try_filter，这样可以获取设备的所有权，异步操作完成后再决定是否保留设备：

use std::{sync::Arc, collections::HashSet};
use futures::{stream::BoxStream, StreamExt,TryStreamExt};
use brightness::{Brightness, BrightnessDevice};

fn get_devices<'a>(device_names: Arc<HashSet<String>>) -> BoxStream<'a, Result<BrightnessDevice, brightness::Error>> {
    if device_names.is_empty() {
        brightness::brightness_devices().boxed()
    } else {
        brightness::brightness_devices()
            .try_filter_map(move |device| {
                let device_names_clone = device_names.clone();
                async move {
                    let devname = device.device_name().await?;
                    Ok(if device_names_clone.contains(&devname) {
                        Some(device)
                    } else {
                        None
                    })
                }
            })
            .boxed()
    }
}

说明 #

try_filter_map允许我们操作流中元素的所有权：

1. 接收流传递的BrightnessDevice所有权
2. 异步调用device_name()获取设备名称
3. 检查名称是否在指定集合中，符合条件则返回Ok(Some(device))保留设备，否则返回Ok(None)丢弃设备
4. 整个过程不再依赖设备的引用，彻底规避了生命周期不匹配的问题

内容的提问来源于stack exchange，提问作者Typhaon