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

Which version of Android are you testing on?

Also, if you were wanted to get behavior similar to a PeriodicWorkRequest, you want to set an initial delay on the Work being enqueued at the end of doWork().

Android 8.

I basically created a PeriodicWorkRequest without the minimum 15min limit - which again, I'm not sure if this is a bug or a feature. This is my code:

override fun doWork(): Worker.WorkerResult {

       // this launch is required to avoid this bug: https://github.com/googlesamples/android-architecture-components/issues/356
        launch {
            Thread.sleep(1)
           
            // from https://github.com/Karn/notify, just to keep it brief and see the app is still alive
            Notify
                .with(applicationContext)
                .content {
                    title = "New dessert menu"
                    text = "The Cheesecake Factory has a new dessert for you to try!"
                }
                .show()
        reloadWorkManager()
        }
        return WorkerResult.SUCCESS
    }


fun reloadWorkManager(){
            WorkManager.getInstance().cancelUniqueWork("work")
       
            val photoWork = OneTimeWorkRequest.Builder(
                SyncWorker::class.java)
                .setInitialDelay(1, TimeUnit.SECONDS)
                .setConstraints(workerConstraints.build())
                .build()

            WorkManager.getInstance().beginUniqueWork("work", ExistingWorkPolicy.REPLACE, photoWork).enqueue()
        }

You will be able to do this in alpha03 using a new method called pruneWork.