Commit 3b1ef1e9 authored Mar 25, 2025 by Steve Elliott

[kairos] guard against coroutine cancelation race

A rare edge case can occur where an observer is added to a BuildScope
that is mid-cancelation, something which is completely valid.

The bug: when adding a completion handler to the build scope's internal
coroutine scope, if this scope is mid-cancellation, then the completion
handler is invoked immediately. This caused an uninitialized variable
`cancelHandle` to be accessed, resulting in a crash.

The solution: remove `lateinit`, make `cancelHandle` nullable, perform
explicit null checking.

Flag: com.android.systemui.status_bar_mobile_icon_kairos
Bug: 383172066
Change-Id: Ie6bb938bef13bb7685b50a19241136bcc575512d

parent f644021a

packages/SystemUI/utils/kairos/src/com/android/systemui/kairos/internal/BuildScopeImpl.kt

+3 −3

Original line number	Diff line number	Diff line
		@@ -113,11 +113,11 @@ internal class BuildScopeImpl(val stateScope: StateScopeImpl, val coroutineScope
		coroutineContext: CoroutineContext,
		block: EffectScope.(A) -> Unit,
		): DisposableHandle {
		val subRef = AtomicReference<Maybe<Output<A>>>(null)
		val subRef = AtomicReference<Maybe<Output<A>>?>(null)
		val childScope = coroutineScope.childScope()
		lateinit var cancelHandle: DisposableHandle
		var cancelHandle: DisposableHandle? = null
		val handle = DisposableHandle {
		cancelHandle.dispose()
		cancelHandle?.dispose()
		subRef.getAndSet(Absent)?.let { output ->
		if (output is Present) {
		@Suppress("DeferredResultUnused")