Fixing concurrent dispatchTo crash

[ouchadam]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Fixes #5821 & #6080

• Uses a safe to concurrently modify structure for the SessionListeners list

Motivation and context

We have a few implementations of the SessionListener which remove themselves from the SessionListeners in onSessionStopped (SessionScopedProperty, InvitesAcceptor) , this is a problem because we iterate through all the listeners in order to call onSessionStopped, resulting in a concurrent modification exception.

The error itself seems to be race condition presenting itself intermittently due to synchronised usages allowing the next main looper to be used, I'm only able to reproduce locally by directly including a listener which removes itself ASAP but the crash is quite common in the Play console

// Session.close()
sessionListeners.addListener(object : Session.Listener {
    override fun onSessionStopped(session: Session) {
        sessionListeners.removeListener(this)
    }
})

The fix is to use a structure which allows concurrent modification, in this case a CopyOnWriteArraySet which does have an extra performance cost but at the point of modification (rather than iteration) which we don't do very often.

Screenshots / GIFs

Before	After

Tests

• In the code, add a new session listener which removes itself onSessionStopped
• Notice a crash when signing out

Tested devices

• Physical
• Emulator
• OS version(s): 28

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication

[bmarty]

LGTM, thanks!

[ouchadam]

for such a tiny change going to merge with 1 👍