Fixed
Status Update
Comments
il...@google.com <il...@google.com> #2
Yigit, do you have time to fix it?
reemission of the same liveData is racy
reemission of the same liveData is racy
an...@gmail.com <an...@gmail.com> #3
yea i'll take it.
ap...@google.com <ap...@google.com> #4
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.
jb...@google.com <jb...@google.com> #5
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()
}
}
an...@gmail.com <an...@gmail.com> #6
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)
ra...@gmail.com <ra...@gmail.com> #7
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} )
}
I actually have a WIP fix for it:
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} )
}
jb...@google.com <jb...@google.com> #8
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
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
Description
Version used: 2.1.0-rc01
Devices/Android versions reproduced on:
Proposal: Safe Arg generated Builder Classes should have default values inside.
This is actually not a bug for navigation component but a kind of side effect which can make this feature more versatile.
In my scenario, we were trying to use generated safe arg Builder classes to pass arguments to the fragments in our project, as the normal bundle arguments are not type safe and kinda messy to work with.
The project I'm working on is relative large, in our team we decided to migrate gradually to navigation component.
As a first step we wanted to put the fragment in a nav graph just to generate safe args so that we can use those classes to safely pass arguments to our existing fragment with fragment transaction and eventually use the graph in future point. So we are trying to use Safe arg as mentioned below:
ChoosePackageFragmentArgs args =
new ChoosePackageFragmentArgs.Builder("testName", "testPackage")
.setIsExtend(true)
.build();
ChoosePackageFragment fragment = new ChoosePackageFragment();
fragment.setArguments(args.toBundle());
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, fragment)
.addToBackStack(null)
.commit();
As you can see from the above example the "isExtend" property is optional and has a default value false which is set in the graph like this,
<argument
android:name="isExtend"
app:argType="boolean"
android:defaultValue="false" />
However if we use the generated safe arg builder class (ChoosePackageFragmentArgs) to pass the arguments to ChoosePackageFragment, without setting "isExtend" the ChoosePackageFragmentArgs.fromBundle(requireArguments()).getIsExtend() throws a NullPointerException because the builder doesn't set the default value when we call the args.toBundle() on the builder instance.
Moreover, when we try to call the getter method it can't find a value from the map, so it tries to cast a null value to (boolean), thus throwing the NullPointerException. Remember we're not using a NavController, just trying to take advantage of SafeArg feature.
This is the code from ChoosePackageFragmentArgs.Builder:
public class ChoosePackageFragmentArgs implements NavArgs {
....
@SuppressWarnings("unchecked")
public boolean getIsExtend() {
return (boolean) arguments.get("isExtend");
}
...
}
We were wondering why the default value is not present in the object. After digging for a while we've found that NavController.navigate() pulls the default values from NavAction.getDefaultArguments(); as we're not using NavComponent we're actually not getting the default value from Builder. Here's the code that pulls default args in NavComponent Library.
Code from NavController.java:
final NavAction navAction = currentNode.getAction(resId);
Bundle combinedArgs = null;
if (navAction != null) {
if (navOptions == null) {
navOptions = navAction.getNavOptions();
}
destId = navAction.getDestinationId();
Bundle navActionArgs = navAction.getDefaultArguments();
if (navActionArgs != null) {
combinedArgs = new Bundle();
combinedArgs.putAll(navActionArgs);
}
}
Suggestion:
If the safe arg plugin added the default values to the Builder while generating those SafeArgs Builder classes, the conventional fragment approach could get huge benefit out of it, and as these classes are accessible apis, I believe it makes more sense to have predictable behaviour for Builder classes as that seems like a standard predictable behaviour.