IssueTracker

Yigit, do you have time to fix it?

reemission of the same liveData is racy

yea i'll take it.

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.

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()
        }
    }

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)

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} )
        }

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

@8 Not sure I see there about Fragments in navigation component, of how to handle it there.
It's mostly about Activities.

Also, speaking of Activities, I can't find a way to support it only to some Activities. Currently it's all-or-nothing, making it very hard to migrate to it and also reduce the appeal of migrating to it (as it requires the entire project to migrate, instead of just what matters).

@9 Please also show samples in fragments within navigation.
In the past when I talked about it, Google actually said (maybe even here in the issue tracker) that it's denied and won't be added.
I don't understand what's going on now.

@12 Was it added recently? I don't remember seeing this.
About the samples, please also add for navigation and maybe also for the navigation-drawer sample.
Even better if you put it in the templates of a new Activity, as this way you could encourage developers to do it.

@14 OK thank you. I wish you'd restore some of the templates there, to show how to use them nowadays.
I learn better from tiny samples than large ones. And those that are shown "on the way" right in the templates of the IDE mean you are serious about them.

Please make sure that we can have all of the possible behaviors of the Predictive Back Gesture when used in a fragment withing the navigation graph:
1. Show the fragment that we will go to when trying to go back
2. Block going to previous fragment (either doesn't exist, or exist and we choose not to allow it) and instead show what's behind in terms of Activity (or app), instead (leaving the current Activity/app)
3. Block back gesture completely, not allowing to go back

Will you please also fix the countless of weird exceptions that appear to this day even on Android 14, related to foreground service?
I've been struggling with it for a very long time. Even found some scenarios for some of the exceptions to occur, and some even contradict the documentation, including even on Pixel devices...

@14 The blocking to going to previous Fragment is important in case the previous Fragment is used as a way to choose which Fragment to reach, and not as UI.
This is something that was said to use instead of clearing the stack itself:
https://issuetracker.google.com/issues/109909461#comment5
https://developer.android.com/guide/navigation/use-graph/conditional

So you wouldn't want to show the MainFragment there, and instead you'd want to allow to skip directly to the Activity behind, even though MainFragment is in the back-stack of the navigation.

Sadly even there on this documentation, there is no sample and there is a lot of missing code.