tokio::fs::File::open errors with "blocking annotated I/O must be called from the context of the Tokio runtime."

[repnop]

Version

Git master branch

Platform

64-bit Windows 10

Subcrates

tokio-fs

Description

Minimal reproduction:

use tokio::fs::File;
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    File::open("Cargo.toml").await?;
    Ok(())
}

This will error with

Error: Custom { kind: Other, error: "`blocking` annotated I/O must be called from the context of the Tokio runtime." }

even when using the default multithreaded runtime. Manually starting the runtime doesn't seem to work either.

[carllerche]

Could you include the list of crates you got pulled in (including deps). Odds are you are mixing git deps & crates.io deps.

[repnop]

Cargo.toml:

[dependencies]
tokio = { git = "https://github.com/tokio-rs/tokio" }

From my Cargo.lock:

[[package]]
name = "tokio"
version = "0.2.0"
source = "git+https://github.com/tokio-rs/tokio#298be802492068d28b972069c5f654de124fd510"
dependencies = [
 "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
 "futures-core-preview 0.3.0-alpha.17 (registry+https://github.com/rust-lang/crates.io-index)",
 "memchr 2.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "num_cpus 1.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "tokio-codec 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-current-thread 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-executor 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-fs 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-io 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-macros 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-reactor 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-sync 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-tcp 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-threadpool 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-timer 0.3.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-udp 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-uds 0.3.0 (git+https://github.com/tokio-rs/tokio)",
 "tracing-core 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
]

[[package]]
name = "tokio-fs"
version = "0.2.0"
source = "git+https://github.com/tokio-rs/tokio#298be802492068d28b972069c5f654de124fd510"
dependencies = [
 "futures-core-preview 0.3.0-alpha.17 (registry+https://github.com/rust-lang/crates.io-index)",
 "tokio-io 0.2.0 (git+https://github.com/tokio-rs/tokio)",
 "tokio-threadpool 0.2.0 (git+https://github.com/tokio-rs/tokio)",
]

[Proximyst]

Would just like to note that the issue doesn't seem to be platform-dependent.

0 proximyst@proximyst-arch:~/tokio_test|HEAD⚡?
λ cargo run
   Compiling tokio_test v0.1.0 (/home/proximyst/tokio_test)
    Finished dev [unoptimized + debuginfo] target(s) in 0.82s
     Running `target/debug/tokio_test`
Error: Custom { kind: Other, error: "`blocking` annotated I/O must be called from the context of the Tokio runtime." }
1 proximyst@proximyst-arch:~/tokio_test|HEAD⚡?
λ uname -a
Linux proximyst-arch 5.1.16-arch1-1-ARCH #1 SMP PREEMPT Wed Jul 3 20:23:07 UTC 2019 x86_64 GNU/Linux

The code is simply the minimal reproduction example.

[carllerche]

Ah! Ok, I see the problem... This is due to #1329...

I'm not sure what the best short term fix... the longer term fix is to finish a bunch of planned work...

[madadam]

I hit this same issue, but with #[tokio::test]. My workaround is to do something like this:

fn main() ->  Result<(), Box<dyn std::error::Error>>  {
    run(async {
        File::open("Cargo.toml").await?;
        Ok(())    
    })
}

fn run<F>(f: F) -> F::Output
where
    F: Future + Send + 'static,
    F::Output: Send + Debug,
{
    let (tx, rx) = tokio::sync::oneshot::channel();
    let rt = tokio::runtime::Runtime::new().unwrap();
    rt.spawn(async move {
        tx.send(f.await).unwrap();
    });
    rt.block_on(rx).unwrap()
}

[eminence]

The tokio::io::Stdin type is impacted by this as well:

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stdin = tokio::io::stdin();
    let mut s = String::new();
    stdin.read_to_string(&mut s).await?;

    Ok(())
}

[carllerche]

Fixed by #1329.

[jebrosen]

Was that supposed to be #1495? I thought #1329 had introduced this error.

[carllerche]

Whoops you are right. Copy / paste fail