[GitHub] [arrow] westonpace commented on pull request #12609: ARROW-15067: [C++] Add tracing spans to the scanner

[GitBox <gi...@apache.org>]

westonpace commented on pull request #12609:
URL: https://github.com/apache/arrow/pull/12609#issuecomment-1068842569


   > And maybe instead of putting Span on Future, it should be attached to the callback itself.
   
   This could work as well.  So every time we add a callback we (while adding the callback) grab the active span.  We then wrap the callback function like...
   
   ```
   auto activeSpan = GetCurrentSpan();
   auto wrapped = [activeSpan, callback] {
     SetCurrentSpan(activeSpan);
     callback();
   };
   ```
   
   (although you'd have to do an actual struct wrapper because `callback` should be move-only and we don't have move lambda captures yet)
   
   I think that's basically the same thing as what I was suggesting on the thread pool but it would only affect futures.  Given most of our thread tasks are futures I think this would probably be acceptable but I think I'd still lean towards implementing this in the executor if I were going to tackle it myself.


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