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

Just a "+1" "me too" to add another voice to this... would make so much sense to be able to have setInitialDelay() on PeriodicWorkRequest.Builder

Android must list down the challenges of Periodic Work request  in there documents, I am  tracking Work Manager since it was alpha.Here are the limitations of Priodic Work request:
1. Periodic work request does not support setInitialDelay.
2. Periodic Work request does not support the Chining.

Both of these items are listed in the official documentation for PeriodicWorkRequest: https://developer.android.com/reference/androidx/work/PeriodicWorkRequest

"Periodic work has a minimum interval of 15 minutes and it cannot have an initial delay."
"Periodic work cannot be part of a chain or graph of work."

Still not supported...
I feel that many people need it...would make so much sense to be able to have setInitialDelay() on PeriodicWorkRequest.Builder

Setting a flex period effectively delays a PeriodicWorkRequest.

+1 from me too, with an extra option to limit the number of repeats, for example, run a periodic job daily for 7 days and then stop.

+1 for setInitailDelay() and limitNumberOfFires() for Periodic work request!

What is the best solution for now to setInitailDelay() ?

You can use a PeriodicWorkRequest.Builder with a flex Period as suggested in #13.
This behaviour is documented: https://developer.android.com/reference/androidx/work/PeriodicWorkRequest.Builder#PeriodicWorkRequest.Builder(java.lang.Class%3C?%20extends%20androidx.work.ListenableWorker%3E,%20long,%20java.util.concurrent.TimeUnit,%20long,%20java.util.concurrent.TimeUnit)

The call creates a PeriodicWorkRequest to run periodically once within the flex period of every interval period.

What I mean by setInitailDelay() is the delay before the first run then a fixed periodic delay.

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

commit 25dc21990f5b0d606f3141b9120516b880599b6c
Author: Rahul Ravikumar <rahulrav@google.com>
Date:   Mon Apr 29 10:27:18 2019

    Add support for initialDelays for PeriodicWorkRequests.
   
    Test: Additional WorkSpecTest unit tests.
    Integration tests on API 23, and API 21.
   
    Fixes: b/111404867
   
    Change-Id: I9eae1c7cf527c231b831f22c6a2d10089d6a63c9

M       work/integration-tests/testapp/src/main/java/androidx/work/integration/testapp/MainActivity.java
M       work/integration-tests/testapp/src/main/res/layout/activity_main.xml
M       work/integration-tests/testapp/src/main/res/values/strings.xml
M       work/workmanager/api/2.1.0-alpha01.txt
M       work/workmanager/api/current.txt
M       work/workmanager/src/androidTest/java/androidx/work/WorkSpecTest.java
M       work/workmanager/src/main/java/androidx/work/OneTimeWorkRequest.java
M       work/workmanager/src/main/java/androidx/work/WorkRequest.java
M       work/workmanager/src/main/java/androidx/work/impl/WorkerWrapper.java
M       work/workmanager/src/main/java/androidx/work/impl/background/systemjob/SystemJobScheduler.java
M       work/workmanager/src/main/java/androidx/work/impl/model/WorkSpec.java

https://android-review.googlesource.com/953484
https://goto.google.com/android-sha1/25dc21990f5b0d606f3141b9120516b880599b6c

still can't rely on it :(
I calculate millis to midnight and schedule a daily backup with PeriodicWorkRequest (should happen each 24h), and it just won't fire up the Worker.
When I remove setInitialDelay() call, PeriodicWorkRequest - it works!

classic