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Comments
ad...@google.com
Yigit, do you have time to fix it?
reemission of the same liveData is racy
reemission of the same liveData is racy
cc...@google.com
yea i'll take it.
rh...@abc.net.au
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.
cc...@google.com
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()
}
}
@Test
fun raceTest() {
val subLiveData = MutableLiveData(1)
val subject = liveData(testScope.coroutineContext) {
emitSource(subLiveData)
emitSource(subLiveData) //crashes
}
subject.addObserver().apply {
testScope.advanceUntilIdle()
}
}
Description
Version used: 27.1.1
Theme used: N/A
Devices/Android versions reproduced on: Any
Regarding the check at the top of `submitList` here:
```
if (newList == mList) {
// nothing to do
return;
}
```
There's a race condition -- suppose we have lists A and B, and the differ's `mList` before starting is list A.
1. Submit list B - async diff generation N kicks off
2. Submit list A - `newList` matches `mList` since diff gen N hasn't completed yet, but `mMaxScheduledGeneration` is not incremented and this returns early
3. Async diff gen N is accepted, despite list A being submitted after list B.
Seems this could be fixed by incrementing `mMaxScheduledGeneration`. As a workaround, I am wrapping my lists in a new identity before submitting them to the differ.