rust - 即使我有＃[tokio::main]，为什么仍然出现错误 “there is no reactor running, must be called from the context of Tokio runtime”？

Question

我遵循the mdns Rust documentation并粘贴了示例代码，但它引发以下错误:

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

这是我的代码:

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,
    }
}

依存关系:

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

我想念什么？我尝试在网上查找，但没有找到如何为该用例创建 react 堆。

Answer 1

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

现在，您将需要匹配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。
也可以看看:

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

具有相同根本原因的各种错误消息:

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