Trace transactions across isolates

[blaugold]

This is a feature that is relevant to Dart and Flutter apps.

I would like to have the ability to trace transactions that perform some work in another isolate and therefore create child spans in that second isolate.

The TimelineTask from dart:developer for example can be used to track tasks that have child tasks in multiple isolates.

[marandaneto]

Indeed, for now, there's a workaround.

// your span Isolate A
final header = spanIsolateA.toSentryTrace()

// pass header to Isolate B
You can use the final spanIsolateB = Sentry.startTransactionWithContext(SentryTransactionContext.fromSentryTrace(header)).

So you are able to continue a transaction from different contexts, that's used for Frontend and Backend stuff, but it works.

[blaugold]

@marandaneto
Thanks for that workaround!

[marandaneto]

We'll do an investigation on how this class Timeline task works and how we could use that to our benefit.
Users could benefit from creating fine-grained spans out of the given transaction/span.
We'll write an update as soon as we come to it.

[marandaneto]

Closing it in favor of #1343
Not really the very same thing but the very same symptom.
I believe we can address both together.