ANR only sends one event

[timfish]

Problem Statement

Currently the ANR feature only sends a single event and exits.

Solution Brainstorm

We chose to do this because:

• The ANR worker does not run a full Sentry client so there's no Dedupe integration
• If ANR has been detected, the event loop is getting blocked for long periods so we shouldn't expend more CPU time than we need to

[joaoviana]

Hey @timfish / Sentry team! Could you clarify this part please? "Currently the ANR feature only sends a single event and exits."
We run a multi-tenant distribution of an app that uses Sentry.
If an ANR event gets capture, and if it's only sent once, what happens for other users? Is it per deployment or per session?

[timfish]

Is it per deployment or per session?

It's currently one event per Node process. I can add an options to lift this limit but there's no easy way to have this per session.

We fetch context (scope, user, tags, etc) from the app thread but we can only do that if it becomes unblocked. If the event loops blocks for more than 5 seconds we give up fetching the extra context and send the event without it.

[abustany]

We're using ANR (with a relatively low threshold of 500ms) to diagnose event loop lags in our NodeJS server, and often get an ANR event during startup while Node is compiling stuff... Which means we never get an ANR event afterwards during the actual event loop stall events 😅 So lifting this limitation (or alternatively adding an option to only start the pings after a given duration) would be super useful!