Why do I need to keep track of the lifetime of the scope/span objects myself?

[Falmarri]

I'm trying to instrument some code that's used in a library that has very specific code flow. Keeping track of the spans and scopes myself is very tricky because I can't pass the spans/scopes. I have to store them in some locally managed storage.

In other tracing libraries (not c++), I've always just been able to do the equivalent of tracer->StartSpan(), and then some time later tracer->CurrentSpan()->End() or whatever. Is there advice on managing scopes if their lifetime is complicated? The only ways I see it working are global state, or polluting the types of all my functions to pass the scope around.

[lalitb]

Is there advice on managing scopes if their lifetime is complicated?

Scope objects are designed to manage the parent-child spans created within the nested functions. It won't work well for anything complicated involving async/threads.

The only ways I see it working are global state, or polluting the types of all my functions to pass the scope around.

Yes sort of. Though you can also use RunTimeStorage to avoid changing the function prototypes in some scenarios.

So to create span in func1() and end in func2(), without passing scope/span objects (not tested to compile):

  void func1() {
    auto span1 = tracer->StartSpan("span1");
    tracer_api::context::RuntimeContext::GetCurrent().SetValue("myspan", span1);
    func2();
 }

 void func2() {
    .... some work
  auto span1 =  context::RuntimeContext::GetCurrent().GetValue("myspan");
  span1->End();
  tracer_api::context::RuntimeContext::GetCurrent().SetValue("myspan", NoopSpan{}); // to remove all references of span1
}

[lalitb]

Also, I think it is worth evaluating if the support can be added to explicitly make the Span current without using a Scope object. Something like:

tracer->UseSpan(tracer->StartSpan("span1"));

And then somewhere else:

tracer->GetCurrentSpan()->End();

Contributions are in-general welcome to add a proposal implementation to discuss further.

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[Falmarri]

Storing in runtime context might work for me. I can activate it when needed, I just can't easily maintain a reference myself.

I am using this though
#1298 (comment) which I understand to be kind of a hack. It does seem to work though

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