What does this PR do?

This fixes a race condition that was quite present in RN - see description below.

The solution I choose was to move the responsibility of checking for initialization from startRecording into checkStatusAndApplySample.
The startRecording method is easier to work with if it just performs an atomic action (like stopRecording).

It seems fit to put the check in checkStatusAndApplySample since it's the method that registers the currentRumSessionId that was creating the lock before.

Motivation

Description of the race condition

This can happen in any Android app, it’s just that conditions for creating the race condition are more present in RN since we collect JS framerate through RUM events on every frame.

The race condition happens in SessionReplayFeature.kt, in the onInitialize function:

        // first line making the race condition possible
        sdkCore.setEventReceiver(SESSION_REPLAY_FEATURE_NAME, this)
        dataWriter = createDataWriter()
        sessionReplayRecorder = sessionReplayRecorderProvider(dataWriter, appContext)
        @Suppress("ThreadSafety") // TODO REPLAY-1861 can be called from any thread
        sessionReplayRecorder.registerCallbacks()
        initialized.set(true) 
        // end of race condition

This is called when we call SessionReplay.enable.

By setting the event receiver, we listen on all RUM events. Now if a RUM event happens before we call initialized.set(true), here is what is going to happen in SessionReplayFeature:

• onReceive is called
• onReceive calls handleRumSession
• handleRumSession calls checkStatusAndApplySample
• checkStatusAndApplySample:
  • calls startRecording since we haven’t started recording
    • startRecording will immediately return since we haven’t called initialized.set(true)
  • calls currentRumSessionId.set(sessionId) at the end of the function to mark the session as started

So far the Session Replay is not recording, and on the next RUM event, even if initialized.set(true) has been called:

• onReceive is called
• onReceive calls handleRumSession
• handleRumSession calls checkStatusAndApplySample
• checkStatusAndApplySample returns before starting the replay since currentRumSessionId.get() == sessionId

So we fail to ever initialize the SDK.

Additional Notes

Anything else we should know when reviewing?

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)