Context confliect in tokio single thread executor

[TommyCpp]

Our trace relays on the Context in thread local storage to store global state. But in tokio single thread executor, everything runs in the same context. Thus, we you spawn a new task, the context will be the same.

Example

use opentelemetry::exporter::trace::stdout;
use opentelemetry::trace::{Tracer, TraceContextExt, StatusCode};
use opentelemetry::{Context, Key};
use std::thread::{spawn, sleep};
use std::borrow::Cow;

fn main() {
    let mut runtime = tokio::runtime::Builder::new().threaded_scheduler().enable_all().build().unwrap();
    runtime.block_on(async {
        let (tracer, _uninstall) = stdout::new_pipeline().install();
        let span = tracer.start("test op1");
        let cx = Context::current_with_span(span);
        let _guard = cx.clone().attach();
        tokio::spawn(async move {
            // in sync enviroment, we will spawn a new thread 
           // and as a result we will have a new Context in a new thread local 
           // but here we are reuse the same context and thread local
            another_operation(None); 
        }).await;
        sleep(std::time::Duration::from_secs(2));
    });
}

fn another_operation(cx: Option<Context>) {
    let cx = Context::current();
    let span = cx.span();
    span.update_name("test op2".to_string());
}

Actually this problem could also occur in multiple thread executors since there is no guarantee which thread task will run on.