RxJava: Error occurred when trying to propagate error to Observer.onError

Question

I am getting a IllegalStateException error in the Rx Library and don't know exactly where the root of the issue is, whether it is with RxJava or something I may be doing incorrectly.

The fatal crash occurs when certificate pinning (occurs on all server requests) but seems to point to a session timeout or logout and back in. Repro steps (occures about 25% of the time) are as follows: login, open list item - scroll all the way end - logout - logback in - open app - close app -> Crash!

Anyone have any ideas on how to prevent this? I found a similar issue here Observer.onError firing off inconsistently

java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.Worker thread.
   at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:62)
   at android.os.Handler.handleCallback(Handler.java:615)
   at android.os.Handler.dispatchMessage(Handler.java:92)
   at android.os.Looper.loop(Looper.java:137)
   at android.app.ActivityThread.main(ActivityThread.java:4867)
   at java.lang.reflect.Method.invokeNative(Method.java)
   at java.lang.reflect.Method.invoke(Method.java:511)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
   at dalvik.system.NativeStart.main(NativeStart.java)
Caused by: rx.exceptions.OnErrorFailedException: Error occurred when trying to propagate error to Observer.onError
   at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:201)
   at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:111)
   at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber$2.call(OperatorObserveOn.java:159)
   at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
   at android.os.Handler.handleCallback(Handler.java:615)
   at android.os.Handler.dispatchMessage(Handler.java:92)
   at android.os.Looper.loop(Looper.java:137)
   at android.app.ActivityThread.main(ActivityThread.java:4867)
   at java.lang.reflect.Method.invokeNative(Method.java)
   at java.lang.reflect.Method.invoke(Method.java:511)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
   at dalvik.system.NativeStart.main(NativeStart.java)
Caused by: rx.exceptions.CompositeException: 2 exceptions occurred. 
   at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:201)
   at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:111)
   at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber$2.call(OperatorObserveOn.java:159)
   at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
   at android.os.Handler.handleCallback(Handler.java:615)
   at android.os.Handler.dispatchMessage(Handler.java:92)
   at android.os.Looper.loop(Looper.java:137)
   at android.app.ActivityThread.main(ActivityThread.java:4867)
   at java.lang.reflect.Method.invokeNative(Method.java)
   at java.lang.reflect.Method.invoke(Method.java:511)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
   at dalvik.system.NativeStart.main(NativeStart.java)
Caused by: rx.exceptions.CompositeException$CompositeExceptionCausalChain: Chain of Causes for CompositeException In Order Received =>
   at com.crashlytics.android.SessionDataWriter.getEventAppExecutionExceptionSize(SessionDataWriter.java:597)
   at com.crashlytics.android.SessionDataWriter.getEventAppExecutionExceptionSize(SessionDataWriter.java:600)
   at com.crashlytics.android.SessionDataWriter.getEventAppExecutionExceptionSize(SessionDataWriter.java:600)
   at com.crashlytics.android.SessionDataWriter.getEventAppExecutionSize(SessionDataWriter.java:533)
   at com.crashlytics.android.SessionDataWriter.getEventAppSize(SessionDataWriter.java:492)
   at com.crashlytics.android.CrashlyticsUncaughtExceptionHandler.writeSessionEvent(CrashlyticsUncaughtExceptionHandler.java:956)
   at com.crashlytics.android.CrashlyticsUncaughtExceptionHandler.access$200(CrashlyticsUncaughtExceptionHandler.java:56)
   at com.crashlytics.android.CrashlyticsUncaughtExceptionHandler$7.call(CrashlyticsUncaughtExceptionHandler.java:274)
   at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
   at java.util.concurrent.FutureTask.run(FutureTask.java:137)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
   at io.fabric.sdk.android.services.common.ExecutorUtils$1$1.onRun(ExecutorUtils.java:58)
   at io.fabric.sdk.android.services.common.BackgroundPriorityRunnable.run(BackgroundPriorityRunnable.java:13)
   at java.lang.Thread.run(Thread.java:856)

Answer 1

What's happening is that your onError implementation in a Subscriber is throwing an unchecked exception which is against the Observable contract and this aborts the observable processing throwing an OnErrorFailedException in the observeOn scheduler.

Answer 2

You are probably passing an Activity context somewhere from your onError callback. This was happening to me when I tried to show an AlertDialog - passing to it a specific Activity context - and pressing back button before that dialog came up. My advice is to not pass Activity contexts this way.

Answer 3

This is how I solved the issue:

public abstract class MyNetworkSubscriber<T> extends Subscriber<T> {

@Override
public void onCompleted() {}

@Override
public void onError(Throwable e) {
    if (e instanceof HttpException) {
        ResponseBody responseBody = ((HttpException) e).response().errorBody();
        try {
            if (responseBody != null) {
                MyError error = new Gson().fromJson(responseBody.string(), MyError.class);
                onErrorCode(error);
            }
        } catch (IOException e1) {
            e1.printStackTrace();
        }
    } else {
        e.printStackTrace();
    }
}

public void onErrorCode(MyError error){};
}

For some reason, OkHttp was forcing me to catch onError so I did. If I did not do this, OkHttp/Retrofit will crash and the app will shut down.

By providing this solution,

1. you can choose to override your own onErrorCode and get a more detailed object back as error which comes from your API but you don't have to.
2. OnError is overridden, no more crazy crashes.
3. And last but not least it is still generic because of <T>!

You can also force onComplete & onError to be overriden to make the methods abstract.

Answer 4

if you want update UI in onError,just try:

api.subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Subscriber(){....})