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-main

commit f5d35eb9ca852dfac791c2dc1d6ce953b2843880
Author: Chris Craik <ccraik@google.com>
Date:   Wed Aug 11 17:35:21 2021

    Move perfetto capture and protos to benchmark-common
   
    Test: ./gradlew benchmark:benchmark-common:cC benchmark:benchmark-macro:cC benchmark:benchmark-macro-junit4:cC benchmark:benchmark-junit4:cC
    Bug: 196115387
    Bug: 145598917
    Relnote: N/A
   
    PerfettoTraceProcessor and its binary will stay in benchmark-macro.
   
    Moves PerfettoRule to benchmark-junit, so that microbenchmarks don't
    need to depend on benchmark-macro-junit4. Eventually, this
    functionality can be merged into BenchmarkRule, as long as
    in-process/app tag tracing is configurable, and off by
    default. UserspaceTracing will enable us to still capture
    BenchmarkState lifecycle events, like different modes (warmup /
    measure / allocation count).
   
    This unblocks raising the minAPI of Macrobench to the long-term goal
    of API 21, which is the lowest that can support shell commands, as
    well as perfetto capture.
   
    This change also moves a few supporting classes, such as DeviceInfo
    and ConfigurationError, which were always intended to gradually
    replace benchmark-common's error / device state querying. This starts
    that process.
   
    As testutils-ktx is used by benchmark-common now, add to all project
    config flavors.
   
    Change-Id: I6559b6735d0106e38ec5d8eaeddcac9297d0c431

M       benchmark/benchmark-common/api/current.txt
M       benchmark/benchmark-common/api/public_plus_experimental_current.txt
M       benchmark/benchmark-common/api/restricted_current.txt
M       benchmark/benchmark-common/build.gradle
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/ConfigurationErrorTest.kt
A       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/Packages.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/ShellBehaviorTest.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/ShellTest.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/UserspaceTracingTest.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/perfetto/AtraceTagTest.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/perfetto/PerfettoConfigTest.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/perfetto/UiStateTest.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/ConfigurationError.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/DeviceInfo.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/UserspaceTracing.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/AtraceTag.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/PerfettoCapture.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/PerfettoCaptureWrapper.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/PerfettoConfig.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/PerfettoHelper.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/UiState.kt
M       benchmark/benchmark-common/src/main/java/perfetto/protos/package-info.java
M       benchmark/benchmark-common/src/main/proto/perfetto_config.proto
M       benchmark/benchmark-common/src/main/proto/perfetto_trace.proto
M       benchmark/benchmark-junit4/api/current.txt
M       benchmark/benchmark-junit4/api/public_plus_experimental_current.txt
M       benchmark/benchmark-junit4/api/restricted_current.txt
M       benchmark/benchmark-junit4/build.gradle
M       benchmark/benchmark-junit4/src/androidTest/java/androidx/benchmark/junit4/PerfettoRuleTest.kt
M       benchmark/benchmark-junit4/src/main/java/androidx/benchmark/junit4/PerfettoRule.kt
M       benchmark/benchmark-macro-junit4/api/current.txt
M       benchmark/benchmark-macro-junit4/api/public_plus_experimental_current.txt
M       benchmark/benchmark-macro-junit4/api/restricted_current.txt
M       benchmark/benchmark-macro/api/current.txt
M       benchmark/benchmark-macro/api/public_plus_experimental_current.txt
M       benchmark/benchmark-macro/api/restricted_current.txt
M       benchmark/benchmark-macro/build.gradle
M       benchmark/benchmark-macro/src/androidTest/java/androidx/benchmark/macro/FileLinkingRule.kt
M       benchmark/benchmark-macro/src/androidTest/java/androidx/benchmark/macro/StartupTimingMetricTest.kt
M       benchmark/benchmark-macro/src/androidTest/java/androidx/benchmark/macro/perfetto/PerfettoCaptureTest.kt
M       benchmark/benchmark-macro/src/androidTest/java/androidx/benchmark/macro/perfetto/PerfettoTraceProcessorTest.kt
M       benchmark/benchmark-macro/src/main/java/androidx/benchmark/macro/CompilationMode.kt
M       benchmark/benchmark-macro/src/main/java/androidx/benchmark/macro/Macrobenchmark.kt
M       benchmark/benchmark-macro/src/main/java/androidx/benchmark/macro/perfetto/PerfettoTraceProcessor.kt
M       benchmark/benchmark/build.gradle
M       benchmark/benchmark/src/androidTest/java/androidx/benchmark/benchmark/PerfettoOverheadBenchmark.kt
M       buildSrc/private/src/main/kotlin/androidx/build/uptodatedness/TaskUpToDateValidator.kt
M       compose/ui/ui-graphics/benchmark/build.gradle
M       compose/ui/ui-graphics/benchmark/src/androidTest/java/androidx/compose/ui/graphics/benchmark/VectorBenchmarkWithTracing.kt
M       development/build_log_simplifier/messages.ignore
M       settings.gradle

https://android-review.googlesource.com/1795168

Project: platform/frameworks/support
Branch: androidx-main

commit ec8b0e22b5e2415f1c165d5ff1b9e73fff4b956b
Author: Chris Craik <ccraik@google.com>
Date:   Fri Nov 19 14:52:10 2021

    Capture Perfetto traces during Microbenchmarks
   
    Bug: 205636583
    Fixes: 145598917
    Test: ./gradlew benchmark-common
    Relnote: "Add low-overhead System Tracing to microbench output on
    Android Q (API 29+). Note that this does not currently capture custom
    tracing (via android.os.Trace or androidx.tracing Jetpack APIs) to
    avoid affecting results. This tracing should be useful in diagnosing
    instability, especially from sources outside the benchmark."
   
    Uses same timing information as microbench itself to generate
    userspace tracing information, which is appended into a captured
    perfetto trace.
   
    Eventually this approach could enable other metrics available in
    traces (such as time a thread is running vs not).
   
    This approach has multiple drawbacks/constraints currently:
   
     * Ignores calls to Trace.beginSection/endSection
         * These have been found to be too high overhead in common
         scenarios to be on by default. Turning it on drastically affected
         many compose benchmarks.
         * Eventually we can either make app tracing tag configurable,
         offer microbenchmark-specific userspace tracing (easier than
         general case, since we can append manually), or offer a more
         general userspace tracing solution (which would also be much
         lower overhead).
     * Puts microbench library tracing in separate track, separate from
       the app process
         * This can be fixed with improvements to the proto generation to
         pick the correct track id, given the test TID .
     * Only traces with bundled perfetto (API 29+)
         * If deemed useful enough, we can use unbundled perfetto as well
         (move perfetto tracebox from benchmark-macro to benchmark-common)
   
    Change-Id: I298be3c9f9f7ef9ba1d2c63d79c864e8c8b16e04

M       benchmark/benchmark-junit4/api/current.txt
M       benchmark/benchmark-junit4/api/restricted_current.txt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/UserspaceTracing.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/MetricCaptureTest.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/InstrumentationResults.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/MetricsContainer.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/PerfettoCaptureWrapper.kt
M       benchmark/benchmark-junit4/src/main/java/androidx/benchmark/junit4/PerfettoRule.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/BenchmarkState.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/InstrumentationResultsTest.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/MetricCapture.kt
M       benchmark/benchmark-junit4/src/main/java/androidx/benchmark/junit4/BenchmarkRule.kt
M       benchmark/benchmark-macro/src/androidTest/java/androidx/benchmark/macro/StartupTimingMetricTest.kt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/perfetto/PerfettoCapture.kt
M       benchmark/benchmark-junit4/api/public_plus_experimental_current.txt
M       benchmark/benchmark-common/src/main/java/androidx/benchmark/Profiler.kt
M       benchmark/benchmark-common/src/androidTest/java/androidx/benchmark/BenchmarkStateTest.kt

https://android-review.googlesource.com/1898071