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

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

commit 0fb5fcd5139c455652796230b7982a9fc63c8f7a
Author: Jeremy Woods <jbwoods@google.com>
Date:   Thu Dec 05 15:03:24 2019

    Adjust the default fragment transition presets
   
    The current fragment transition presets did not take into consideration
    that fragments rarely have a non-opaque background. This change adjusts
    the fragment presets with specifications specifically for fragments.
   
    The open and close transitions now have a duration of 300 instead of 400
    and the fade transition has a duration of 150. The open transition fades
    the exiting view to an alpha of 0 instead of 0.4.
   
    Test: Tested in muliple applications
    BUG: 145468417
    Change-Id: I6e1be474d0bb218e4a519bb09ea5bc1fc1757dcf

M       fragment/fragment/src/main/res/anim/fragment_close_enter.xml
M       fragment/fragment/src/main/res/anim/fragment_close_exit.xml
M       fragment/fragment/src/main/res/anim/fragment_fade_enter.xml
M       fragment/fragment/src/main/res/anim/fragment_fade_exit.xml
M       fragment/fragment/src/main/res/anim/fragment_open_enter.xml
M       fragment/fragment/src/main/res/anim/fragment_open_exit.xml

https://android-review.googlesource.com/1183003

This has been fixed internally and will be available in the Fragment 1.2.0-rc04 release.

Here is how the new presets will look given sample app from #4.

Thanks, that looks much better!

  The following changes were cherrypicked through Coastguard (https://android-build.googleplex.com/coastguard/)
  Release Track: (https://android-build.googleplex.com/coastguard/dashboard/6552735953321984/#/history/all)
  Created: 2019-12-09 19:09:00.495077+00:00
  Changes: aosp/1183003