provide examples

[softprops]

I'm reading the structure of this crate to understand the pieces but I feel like I'm missing parts. It may be helpful to provide some cargo /examples application to demonstrate how these pieces fit together

[sfackler]

Sure - I think a little toy HTTP server would make sense as a decent example.

[softprops]

In particular I'm wanting to see how to transfer contexts across threads. Since CurrentGuard can't be Send, I'm missing what the pattern in practice looks like

[sfackler]

If you have an OpenSpan and want to fully transfer it to the other thread, you can use the detach and attach methods:

let span = my_tracer.next_span()
    .with_name("background-thingy")
    .detach();

thread::spawn(move || {
    let span = span.attach();
    // do stuff...
});

If you don't have an OpenSpan (or have one but don't want to transfer ownership), you can just grab the context from it and send that to the other thread:

let context = current_guard.context();

thread::spawn(move || {
    let current_guard = tracer.set_current(context);
    // do stuff...
});

[softprops]

In that first example, does the span information associated with "background-thing" get discarded when detaching? It seems the both detach/attach operations discard any built up span state. When attaching, it seems all operations on the open span would have no effect. I'm I understanding this right?

[sfackler]

No, attaching and detaching doesn't discard any state. The only thing it changes is if the OpenSpan acts as a CurrentGuard in addition.

[softprops]

I'm looking to understand the use of mem::replace here

[sfackler]

Detach consumes the old OpenSpan by value and returns a new one with the span's state.

[softprops]

Ah I see. Thanks!