Zbus still spawns a second thread even with internal executor disabled

[germaniuss]

Not sure if this is a bug but there seems to be another thread being spawned besides de internal executor. Enabling the tokio feature or setting internal executor to false does not get rid of it. I have not found anywhere in the documentation any mention of zbus spawning another thread besides de internal executor.

#[tokio::main(flavor = "current_thread")]
async fn main() -> Result<(), Box<dyn Error>> {
    let conn = zbus::Connection::session().await?;
    let mut sigint = signal(SignalKind::interrupt())?;
    sigint.recv().await;
    Ok(())
}

Tokio disabled:

Tokio enabled:

So where is that second thread coming from? Is there a way to run just a single thread? It's not great having to use another thread for my usecase since it's fairly simple and I don't want to use extra resources I don't need.

[zeenix]

Your code is not disabling the internal executor:

zbus::Connection::session().await

You need to use the builder:

https://docs.rs/zbus/latest/zbus/connection/struct.Builder.html#method.session

https://docs.rs/zbus/latest/zbus/connection/struct.Builder.html#method.internal_executor

[germaniuss]

But I'm using the tokio feature in cargo.toml which should disable the internal executor (if I disable the executor manually it's the same, I tried).

Anyhow after looking into it, it seems this thread only exists at app startup and then disappears. I believe it's the spawn_blocking call that exists to call let stream = UnixStream::connect_addr(&addr)?; and it just takes a while to cleanup the thread. It would be better to use tokio::net::UnixStream and async_net::UnixStream but I guess its not used because it does not implement SocketAddrExt

Anyways I'll close this issue.

EDIT:

To be clear I am talking about this block of code

let stream = crate::Task::spawn_blocking(
    move || -> Result<_> {
        #[cfg(unix)]
        let stream = UnixStream::connect_addr(&addr)?;
        #[cfg(windows)]
        let stream = UnixStream::connect(addr)?;
        stream.set_nonblocking(true)?;
        Ok(stream)
    },
    "unix stream connection",
)

[germaniuss]

@zeenix It seems that tokio has had abstract socket name support for a while now. Would you mind me opening a PR to use tokio::net::UnixStream when using tokio and avoid spinning up an extra thread?

tokio-rs/tokio#6772

[zeenix]

@zeenix It seems that tokio has had abstract socket name support for a while now. Would you mind me opening a PR to use tokio::net::UnixStream when using tokio and avoid spinning up an extra thread?

tokio-rs/tokio#6772

I don't understand. We have Socket impl for tokio::net::UnixStream (enabled by the tokio feature) and this is irrelevant to threads AFAIK. Could you please elaborate?

[zeenix]

@zeenix It seems that tokio has had abstract socket name support for a while now. Would you mind me opening a PR to use tokio::net::UnixStream when using tokio and avoid spinning up an extra thread?

tokio-rs/tokio#6772

I don't understand. We have Socket impl for tokio::net::UnixStream (enabled by the tokio feature) and this is irrelevant to threads AFAIK. Could you please elaborate?

Oh, I had missed your previous comment, sorry.

A PR would be appreciated, yes. 🙏