Calling render inside Appsignal instrument breaks the span stack and fails to report the trace

[tombruijn]

From my notes in Slack.

In a Phoenix controller, doing this breaks the reporting for that action:

Appsignal.instrument("event.group", fn span ->
  render(conn, :home)
end)

Order of events:

• phoenix_endpoint_start
• phoenix_router_dispatch_start
• Appsignal.instrument - start
• phoenix_endpoint_stop:
  • This is called here because of render inside Appsignal.instrument
  • This event closes the span from Appsignal.instrument as it's the current span
• Appsignal.instrument - stop:
  • This moment closes the same span again as the last step, not the current span (which would also be wrong)
• phoenix_router_dispatch_stop:
  • This closes the span from phoenix_router_dispatch_start, instead of what it should be closing: phoenix_endpoint_start

The Phoenix events are from our Phoenix package.

Fix it somehow in our Phoenix event handler.

[tombruijn]

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