Custom Instrumentation produces unreliable data

[ehu0716]

Platform

iOS

Environment

Production

Installed

Swift Package Manager

Version

8.37

Xcode Version

16.0

Did it work on previous versions?

No response

Steps to Reproduce

Our team are employing custom instrumentation to assess the performance of a specific function in our application. However, the data displayed on the dashboard is highly inaccurate, with numerous entries showing durations of days or even weeks, and many others indicating a duration of 0 milliseconds. This makes the data unreliable for evaluating performance effectively.

Expected Result

We shouldn't see data with duration of days, weeks or 0ms.

Actual Result

Wrong data

Are you willing to submit a PR?

No response

[brustolin]

Hello @ehu0716, thanks for reaching out.

Can you share more how are you using custom instructions? Maybe share a repro with us.
Its usage relies heavily on your own strategy, and without knowing your code base we cannot help you.

[ehu0716]

Hey @brustolin, thanks for your reply. I can't share the repo with you unfortunately. But we did a really basic custom instrumental with following implementation during App launch.

sentryTransaction = SentrySDK.startTransaction(
            name: "Transaction",
            operation: "init"
        )
sentrySpan = sentryTransaction?.startChild(operation: "span")
one function we want to measure 
sentrySpan?.finish()
sentryTransaction?.finish()

I suspect that while the sentrySpan starts and before the finish method is called, if the user moves the app to the background, the finish method might not be executed until the app is brought back to the foreground. Do you think this is possible?

[brustolin]

Hello @ehu0716.
I meant a way to reproduce the problem, not the repository, my bad if it was not well communicated.

And thants for the repro. I dont think moving the app to the background would halt the function in such way, but I need to test.

But aren't you using something like this:

do {
  sentryTransaction = SentrySDK.startTransaction(
              name: "Transaction",
              operation: "init"
          )
  sentrySpan = sentryTransaction?.startChild(operation: "span")
  try functionToMeasure()
  sentrySpan?.finish()
  sentryTransaction?.finish()
} catch {

}

In this case, if the function throws an exception, the span is never finished, and if the user moves the app to the background and comes back later, somehow you finish the span, then I believe you would end up with the scenario that you described.

[ehu0716]

@brustolin 😓 my bad, misread your initial reply.
That is a good guess. But we are not wrapping code in do catch. so I reckon my assumption doesn't stand.

[brustolin]

Got it. We will investigate this.