Rust中for_each内生命周期问题求解：Inotify事件发送编译失败

原问题代码 #

尝试实现基于inotify的目录监控时，最初希望通过无拷贝的&OsStr传递事件文件名，因此给Watcher结构体添加了生命周期标注，但仍无法通过for_each中的编译检查，原代码如下：

use std::{sync::mpsc::Sender, ffi::OsStr};

use inotify::{Event, EventMask, Inotify, WatchMask};

pub struct Watcher<'a> {
    buffer: [u8; 1024],
    sender: Sender<Event<&'a OsStr>>,
}

impl<'a> Watcher<'a> {
    pub fn new(sender: Sender<Event<&OsStr>>) -> Watcher{
        Watcher{
            buffer: [0; 1024],
            sender: sender,
        }
    }
    pub fn watch_for_led_directories(&mut self, dir: String) {
        let sender = self.sender.clone();
        let mut inotify = Inotify::init().expect("Error while initializing inotify instance");

        // Watch for modify and close events.
        inotify
            .add_watch(dir, WatchMask::CREATE | WatchMask::DELETE)
            .expect("Failed to add file watch");

        // Read events that were added with `add_watch` above.
        
        let events = inotify
            .read_events_blocking(&mut self.buffer)
            .expect("Error while reading events");

        events.filter(|e| -> bool { !e.mask.intersects(EventMask::ISDIR) }).for_each(|e| sender.send(e).unwrap());
    }
}

问题核心 #

read_events_blocking返回的事件中，&OsStr的引用生命周期仅绑定到&mut self.buffer的临时作用域（当前方法调用内有效），但Sender<Event<&'a OsStr>>要求引用拥有'a（即Watcher实例的整个生命周期），两者生命周期不匹配。mpsc通道的发送是异步的，无法保证引用在接收方使用时仍然有效，因此编译器拒绝这种不安全操作。

最终解决方案（采用所有权转移） #

放弃无拷贝方案，改用拥有所有权的String传递文件名，无需处理引用生命周期，代码如下：

use std::{ffi::OsStr, sync::mpsc::Sender};

use inotify::{Event, EventMask, Inotify, WatchMask};

pub struct Watcher {
    buffer: [u8; 1024],
    sender: Sender<Event<String>>,
}

impl Watcher {
    pub fn new(sender: Sender<Event<String>>) -> Watcher {
        Watcher {
            buffer: [0; 1024],
            sender: sender,
        }
    }
    pub fn watch_for_led_directories(&mut self, dir: String) {
        let sender = self.sender.clone();
        let mut inotify = Inotify::init().expect("Error while initializing inotify instance");

        // Watch for modify and close events.
        inotify
            .add_watch(dir, WatchMask::CREATE | WatchMask::DELETE)
            .expect("Failed to add file watch");

        // Read events that were added with `add_watch` above.

        let events = inotify
            .read_events_blocking(&mut self.buffer)
            .expect("Error while reading events");

        let filter = |e: &Event<&OsStr>| -> bool {
            !e.mask.intersects(EventMask::ISDIR) || e.name.is_none()
        };
        events.filter(filter).for_each(|e| {
            sender
                .send(Event {
                    cookie: e.cookie,
                    mask: e.mask,
                    name: e.name.and_then(|name| name.to_str().map(String::from)),
                    wd: e.wd,
                })
                .unwrap()
        });
    }
}

修改说明 #

1. 移除Watcher的生命周期参数，简化结构体定义
2. 将Sender类型改为Sender<Event<String>>，通过所有权转移保证数据安全
3. 事件处理时，用and_then替代unwrap转换文件名，避免非Unicode文件名导致崩溃；若需支持非Unicode场景，可改用OsString替代String

内容的提问来源于stack exchange，提问作者abergmeier