Strict Mode DiskReadViolation on Android when converting Rx Publisher to Flow

[mhernand40]

I have some code that is converting an Observable to a Flow in the following manner:

myObservable.toFlowable(BackpressureStrategy.LATEST).asFlow()

I cannot reproduce on my own test device but someone else on my team was able to reproduce the following Strict Mode violation:

android.os.strictmode.DiskReadViolation
        at android.os.StrictMode$AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1504)
        at java.io.UnixFileSystem.getLength(UnixFileSystem.java:265)
        at java.io.File.length(File.java:970)
        at java.util.zip.ZipFile.<init>(ZipFile.java:212)
        at java.util.zip.ZipFile.<init>(ZipFile.java:152)
        at java.util.jar.JarFile.<init>(JarFile.java:160)
        at java.util.jar.JarFile.<init>(JarFile.java:97)
        at libcore.io.ClassPathURLStreamHandler.<init>(ClassPathURLStreamHandler.java:47)
        at dalvik.system.DexPathList$Element.maybeInit(DexPathList.java:702)
        at dalvik.system.DexPathList$Element.findResource(DexPathList.java:729)
        at dalvik.system.DexPathList.findResources(DexPathList.java:526)
        at dalvik.system.BaseDexClassLoader.findResources(BaseDexClassLoader.java:174)
        at java.lang.ClassLoader.getResources(ClassLoader.java:839)
        at java.util.ServiceLoader$LazyIterator.hasNextService(ServiceLoader.java:349)
        at java.util.ServiceLoader$LazyIterator.hasNext(ServiceLoader.java:402)
        at java.util.ServiceLoader$1.hasNext(ServiceLoader.java:488)
        at kotlin.collections.CollectionsKt___CollectionsKt.toCollection(_Collections.kt:1155)
        at kotlin.collections.CollectionsKt___CollectionsKt.toMutableList(_Collections.kt:1188)
        at kotlin.collections.CollectionsKt___CollectionsKt.toList(_Collections.kt:1179)
        at kotlinx.coroutines.reactive.ReactiveFlowKt.<clinit>(ReactiveFlow.kt:138)
        at kotlinx.coroutines.reactive.ReactiveFlowKt.asFlow(Unknown Source:0)

It points to the following top-level property which performs some static initialization within ReactiveFlow.kt:

// ContextInjector service is implemented in `kotlinx-coroutines-reactor` module only.
// If `kotlinx-coroutines-reactor` module is not included, the list is empty.
private val contextInjectors: List<ContextInjector> =
    ServiceLoader.load(ContextInjector::class.java, ContextInjector::class.java.classLoader).toList()

[qwwdfsad]

This is an improper use of SL on our side. This code is invoked once per application, so as a temporary workaround you can first invoke asFlow from any thread except the main thread

[tclift]

I think this still occurs, because contextInjectors can be initialised on access. The first access can be an asFlow call from the main thread.

This worked for me as a workaround (near app start):

runBlocking(Dispatchers.IO) {
    Flowable.empty<Void>().asFlow()
}

[yigit]

I'm not sure if r8 is the right solution here, if coroutines are initialized after the stricty mode is set, this still happens:

To reproduce:

class SomeActivity : AppCompatActivity {
  override fun onCreate(savedInstanceState: Bundle?) {
        StrictMode.setThreadPolicy(
            StrictMode.ThreadPolicy.Builder()
                .detectDiskReads()
                .detectDiskWrites()
                .penaltyDeath()
                .build()
        )
        runBlocking {  } // it will crash here. moving runBlocking above the StrictMode block fixes the issue.
  }
}

Stacktrace:

    java.lang.ExceptionInInitializerError
        at kotlinx.coroutines.CoroutineExceptionHandlerImplKt.initializeDefaultExceptionHandlers(CoroutineExceptionHandlerImpl.kt:27)
        at kotlinx.coroutines.Job.<clinit>(Job.kt:120)
        at kotlinx.coroutines.AbstractCoroutine.<init>(AbstractCoroutine.kt:51)
        at kotlinx.coroutines.BlockingCoroutine.<init>(Builders.kt:66)
        at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:57)
        at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source:1)
        at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
        at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source:1)
        at SomeActivity.onCreate(SomeActivity.kt:57)
        at android.app.Activity.performCreate(Activity.java:7994)
        at android.app.Activity.performCreate(Activity.java:7978)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)