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 bab31cacd4ae98057b694f6ae4c781f5f25ee0c9
Author: Yigit Boyar <yboyar@google.com>
Date:   Wed Oct 31 23:41:00 2018

    Fix live data observe forever in room
   
    This CL fixes a problem where if DAO returned LiveData is
    observed with observeForever but there are no references
    to the LiveData, it would eventually be garbage collected.
   
    To avoid this, InvalidationTracker now manages these LiveData
    objects and strongly references them as long as there is an
    active observer.
    To be 100%, we should actually do it when LiveData has observers
    but right now that API does not exist in the LiveData side
    to get notified when the observer count changes 0 and 1.
   
    I've also cleaned up some test code to avoid duplicating the
    test observers in each test.
   
    I've also added an integration test that uses room w/o any of
    the optional dependencies to ensure that we don't break the
    contract on compileOnly dependencies.
   
    Bug: 74477406
    Test: LiveDataQueryTest, InvalidationTrackerTest, NoAppCompatTestApp
    Change-Id: If88114306d7e20ddaed0312a1203a0d14b710145

M       arch/core-testing/src/main/java/androidx/arch/core/executor/TaskExecutorWithFakeMainThread.java
M       room/compiler/src/main/kotlin/androidx/room/solver/query/result/LiveDataQueryResultBinder.kt
M       room/compiler/src/test/data/daoWriter/output/ComplexDao.java
A       room/integration-tests/noappcompattestapp/.gitignore
A       room/integration-tests/noappcompattestapp/README.md
A       room/integration-tests/noappcompattestapp/build.gradle
A       room/integration-tests/noappcompattestapp/src/androidTest/java/androidx/room/integration/noappcompat/BareDatabaseTest.java
A       room/integration-tests/noappcompattestapp/src/main/AndroidManifest.xml
A       room/integration-tests/noappcompattestapp/src/main/java/androidx/room/integration/noappcompat/BareDatabase.java
M       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/paging/DataSourceFactoryTest.java
M       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/InvalidationTrackerTest.java
M       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/LiveDataQueryTest.java
M       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/QueryTransactionTest.java
A       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/TestLifecycleOwner.java
A       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/TestObserver.java
M       room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/TestUtil.java
M       room/runtime/build.gradle
A       room/runtime/src/main/java/androidx/room/InvalidationLiveDataContainer.java
M       room/runtime/src/main/java/androidx/room/InvalidationTracker.java
A       room/runtime/src/main/java/androidx/room/RoomTrackingLiveData.java
A       room/runtime/src/test/java/androidx/room/InvalidationLiveDataContainerTest.kt
M       room/runtime/src/test/java/androidx/room/InvalidationTrackerTest.java
M       settings.gradle

https://android-review.googlesource.com/810053
https://goto.google.com/android-sha1/bab31cacd4ae98057b694f6ae4c781f5f25ee0c9

FYI this requires client to update to Room 2.1.0-alpha03 but it is fully compatible with 1.x that WM uses.

actually it won't work because the change is in generated code. I'll try to backport itinto WM.

re-opening for WM part.

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

commit 3fb46bd8602faaf9c34aa969f8ae589c251c2f72
Author: Yigit Boyar <yboyar@google.com>
Date:   Fri Nov 30 13:19:34 2018

    Track LiveData returned by the WM
   
    This CL works around a bug in Room 1.x where LiveData returned
    by Room might be garbage collected.
   
    Now work manager tracks any live data it returns as long as the
    LiveData is active.
   
    Bug: 74477406
    Test: ObserForeverTest, WorkManagerLiveDataTrackerTest
    Change-Id: I1e45dade1e8a3c29d6c35f7cb0c6e072c68ee658

A       work/workmanager/src/androidTest/java/androidx/work/impl/ObserveForeverTest.java
M       work/workmanager/src/main/java/androidx/work/impl/WorkManagerImpl.java
A       work/workmanager/src/main/java/androidx/work/impl/WorkManagerLiveDataTracker.java
A       work/workmanager/src/test/java/androidx/work/impl/WorkManagerLiveDataTrackerTest.java

https://android-review.googlesource.com/838833
https://goto.google.com/android-sha1/3fb46bd8602faaf9c34aa969f8ae589c251c2f72