Lifecycle as Flow [176311030]

Fixed

Feature Request

Status Update

No update yet.

Description

p1...@gmail.com

created issue #1

Dec 25, 2020 09:24PM

Please provide extension for lifecycle to observe Lifecycle.Event as Flow.

Also present you my workaround

fun Lifecycle.asFlow() = callbackFlow<Lifecycle.Event> {

val observer = ALifecycleObserver(this@asFlow) { offer(it) }

awaitClose { removeObserver(observer) }

}

class ALifecycleObserver(
lifecycle: Lifecycle,
private val action: (Lifecycle.Event) -> Unit
): LifecycleObserver {

init { lifecycle.addObserver(this) }

@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
fun onCreate(event: Lifecycle.Event) = action.invoke(event)

@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onStart(event: Lifecycle.Event) = action.invoke(event)

@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
fun onResume(event: Lifecycle.Event) = action.invoke(event)

@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
fun onPause(event: Lifecycle.Event) = action.invoke(event)

@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onStop(event: Lifecycle.Event) = action.invoke(event)

@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun onDestroy(event: Lifecycle.Event) = action.invoke(event)
}

Comments

p1...@gmail.com <p1...@gmail.com> #2Dec 25, 2020 11:24PM

Yigit, do you have time to fix it?

reemission of the same liveData is racy

se...@google.com <se...@google.com> #3Jan 6, 2021 01:22PM

yea i'll take it.

p1...@gmail.com <p1...@gmail.com> #4Jan 6, 2021 01:54PM

Thanks for the detailed analysis. This may not be an issue anymore since we've started using Main.immediate there but I' not sure; I'll try to create a test case.

il...@google.com <il...@google.com> Nov 18, 2021 10:12PM

Status: New

ca...@google.com <ca...@google.com> #5Jan 28, 2022 06:40PM

just emitting same live data reproduces the issue.

@Test
fun raceTest() {
val subLiveData = MutableLiveData(1)
val subject = liveData(testScope.coroutineContext) {
emitSource(subLiveData)
emitSource(subLiveData) //crashes
}
subject.addObserver().apply {
testScope.advanceUntilIdle()
}
}

il...@google.com <il...@google.com> Sep 12, 2022 11:51PM

Assigned to sa...@google.com.

ey...@gmail.com <ey...@gmail.com> #6Jan 17, 2023 10:59PM

With 2.2.0-alpha04 (that use Main.immediate), the issue seems to be still there (I tested it by calling emitSource() twice, like your test case)

it...@gmail.com <it...@gmail.com> #7Jan 20, 2023 01:16AM

yea sorry immediate does not fix it.
I actually have a WIP fix for it:

https://android-review.googlesource.com/c/platform/frameworks/support/+/1112186

if your case is the one i found (emitting same LiveData multiple times, as shown in #5) you can work around it by adding a dummy transformation.

val subLiveData = MutableLiveData(1)
val subject = liveData(testScope.coroutineContext) {
emitSource(subLiveData.map {it })
emitSource(subLiveData.map {it} )
}

sa...@google.com <sa...@google.com> Feb 8, 2023 10:41PM

Accepted by sa...@google.com.

ap...@google.com <ap...@google.com> #8Mar 3, 2023 10:24PM

Project: platform/frameworks/support
Branch: androidx-master-dev

commit af12e75e6b4110f48e44ca121466943909de8f06
Author: Yigit Boyar <yboyar@google.com>
Date: Tue Sep 03 12:58:11 2019

Fix coroutine livedata race condition

This CL fixes a bug in liveData builder where emitting same
LiveData source twice would make it crash because the second
emission registry could possibly happen before first one is
removed as source.

We fix it by using a suspending dispose function. It does feel
a bit hacky but we cannot make DisposableHandle.dispose async
and we do not want to block there. This does not mean that there
is a problem if developer disposes it manually since our emit
functions take care of making sure it disposes (and there is
no other way to add source to the underlying MediatorLiveData)

Bug: 140249349
Test: BuildLiveDataTest#raceTest_*

Change-Id: I0b464c242a583da4669af195cf2504e2adc4de40

M lifecycle/lifecycle-livedata-ktx/api/2.2.0-alpha05.txt
M lifecycle/lifecycle-livedata-ktx/api/current.txt
M lifecycle/lifecycle-livedata-ktx/api/public_plus_experimental_2.2.0-alpha05.txt
M lifecycle/lifecycle-livedata-ktx/api/public_plus_experimental_current.txt
M lifecycle/lifecycle-livedata-ktx/api/restricted_2.2.0-alpha05.txt
M lifecycle/lifecycle-livedata-ktx/api/restricted_current.txt
M lifecycle/lifecycle-livedata-ktx/src/main/java/androidx/lifecycle/CoroutineLiveData.kt
M lifecycle/lifecycle-livedata-ktx/src/test/java/androidx/lifecycle/BuildLiveDataTest.kt

https://android-review.googlesource.com/1112186

https://goto.google.com/android-sha1/af12e75e6b4110f48e44ca121466943909de8f06

it...@gmail.com <it...@gmail.com> #9Mar 4, 2023 12:18AM

#8 you might want to remove that email from your comment, as emails are typically obfuscated in these threads

sa...@google.com <sa...@google.com> Mar 6, 2023 07:43PM

Marked as fixed.

na...@google.com <na...@google.com> #10Jul 26, 2023 05:21PM

The following release(s) address this bug.It is possible this bug has only been partially addressed:

androidx.lifecycle:lifecycle-common:2.7.0-alpha01
androidx.lifecycle:lifecycle-runtime-testing:2.7.0-alpha01