How to report/flush open spans at end of application

[wcarmon]

At the end of my main fn, I noticed the root span wasn't being reported (ended). (probably because they report on a background thread)

I added a brief delay to allow some time, but it's hacky

fn main() {
    do_the_important_stuff();

    // -- give app some time to report any open spans
    sleep(Duration::from_millis(250));
}

For OpenTelemetry, I see opentelemetry::global::shutdown_tracer_provider();, that is otel specific though.

Is there a tracing way to flush/cleanup?

[davidbarsky]

The core tracing libraries aren't really aware of writers beyond MakeWriter inside of tracing-subscriber. There's a lot of ways to tackle this problem that's idiosyncratic to each Layer/Subscriber, runtime, and constraints (e.g., std/no_std) and I don't think it's the best use of time/resources for tracing to focus on this now.

That being said, depending on what writer you're using (e.g., tracing-appender), you can use https://docs.rs/tracing-appender/latest/tracing_appender/non_blocking/struct.WorkerGuard.html to ensure flushes, but if you're writing to stdout/stderr, you really shouldn't be seeing dropped spans.