为什么我收到错误“没有反应器正在运行，必须从 Tokio 运行时的上下文中调用"?即使我有#[tokio::main]? [英] Why do I get the error "there is no reactor running, must be called from the context of Tokio runtime" even though I have #[tokio::main]?

问题描述

我正在关注 mdns Rust 文档 并粘贴了示例代码，但它抛出以下错误:

线程main"因没有反应器在运行，必须从 Tokio 运行时的上下文中调用"而恐慌

这是我拥有的代码:

use futures_util::{pin_mut, stream::StreamExt};使用 mdns::{Error, Record, RecordKind};使用 std::{net::IpAddr, time::Duration};const SERVICE_NAME: &'static str = "_googlecast._tcp.local";#[东京::主要]async fn main() ->结果<()，错误>{//迭代来自每个 Cast 设备的响应，每 15 秒请求一次新设备让流 = mdns::discover::all(SERVICE_NAME, Duration::from_secs(15))?.listen();pin_mut!(流);而让 Some(Ok(response)) = stream.next().await {让 addr = response.records().filter_map(self::to_ip_addr).next();如果让 Some(addr) = addr {println!(在{}找到投射设备"，地址);} 别的 {println!(投射设备不通告地址");}}好的(())}fn to_ip_addr(record: &Record) ->选项{匹配记录.种类{RecordKind::A(addr) =>一些(addr.into())，RecordKind::AAAA(addr) =>一些(addr.into())，_ =>没有任何，}}

依赖:

[依赖项]mdns = "1.1.0";期货-util =0.3.8"；tokio = { version = "0.3.3", features = ["full"] }

我错过了什么?我尝试在网上查找，但还没有找到如何为此用例创建反应器.

解决方案

您使用的是较新版本的 Tokio，例如 0.3 或 1.x，并且许多软件包(包括 mdns 1.1.0)依赖于较旧版本的Tokio，比如0.2.

% cargo tree -d东京 v0.2.22└── mdns v1.1.0└── example_project v0.1.0东京 v0.3.3└── example_project v0.1.0

目前，您需要匹配 Tokio 运行时的版本.最简单的方法是自己使用 Tokio 0.2.tokio-compat-02 crate 在某些情况下也可能有用.

另见:

• 为什么没有为明确实现的类型实现特性?

---

具有相同根本原因的各种错误消息:

<块引用>

没有反应器在运行，必须从 Tokio 1.x 运行时的上下文中调用

<块引用>

没有反应器在运行，必须从 Tokio 运行时的上下文中调用

<块引用>

当前未在 Tokio 运行时上运行

I'm following the mdns Rust documentation and pasted the example code but it throws the following error:

thread 'main' panicked at 'there is no reactor running, must be called from the context of Tokio runtime'

Here's the code that I have:

use futures_util::{pin_mut, stream::StreamExt};
use mdns::{Error, Record, RecordKind};
use std::{net::IpAddr, time::Duration};

const SERVICE_NAME: &'static str = "_googlecast._tcp.local";

#[tokio::main]
async fn main() -> Result<(), Error> {
    // Iterate through responses from each Cast device, asking for new devices every 15s
    let stream = mdns::discover::all(SERVICE_NAME, Duration::from_secs(15))?.listen();
    pin_mut!(stream);

    while let Some(Ok(response)) = stream.next().await {
        let addr = response.records().filter_map(self::to_ip_addr).next();

        if let Some(addr) = addr {
            println!("found cast device at {}", addr);
        } else {
            println!("cast device does not advertise address");
        }
    }

    Ok(())
}

fn to_ip_addr(record: &Record) -> Option<IpAddr> {
    match record.kind {
        RecordKind::A(addr) => Some(addr.into()),
        RecordKind::AAAA(addr) => Some(addr.into()),
        _ => None,
    }
}

Dependencies:

[dependencies]
mdns = "1.1.0"
futures-util = "0.3.8"
tokio = { version = "0.3.3", features = ["full"] }

What am I missing? I tried looking online but haven't found how to create a reactor for this use case.

解决方案

You are using a newer version of Tokio, such as 0.3 or 1.x, and many packages, including mdns 1.1.0, rely on an older version of Tokio, such as 0.2.

% cargo tree -d
tokio v0.2.22
└── mdns v1.1.0
    └── example_project v0.1.0

tokio v0.3.3
└── example_project v0.1.0

For now, you will need to match versions of the Tokio runtime. The easiest way is to use Tokio 0.2 yourself. The tokio-compat-02 crate may also be useful in some cases.

See also:

• Why is a trait not implemented for a type that clearly has it implemented?

---

Various error messages with the same root cause:

there is no reactor running, must be called from the context of a Tokio 1.x runtime

there is no reactor running, must be called from the context of Tokio runtime

not currently running on the Tokio runtime

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