java.lang.NullPointerException: Attempt to invoke interface method 'boolean io.reactivex.internal.fuseable.SimpleQueue.isEmpty()' on a null object reference

[ivnsch]

I get this exception sometimes. It can't be reproduced reliably. Can't find any reference to my code, so I have no idea what's causing it:

java.lang.IllegalStateException: Fatal Exception thrown on Scheduler. at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:113) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'boolean io.reactivex.internal.fuseable.SimpleQueue.isEmpty()' on a null object reference at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.drainNormal(ObservableObserveOn.java:172) at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.run(ObservableObserveOn.java:252) at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:111) at android.os.Handler.handleCallback(Handler.java:751)  at android.os.Handler.dispatchMessage(Handler.java:95)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6119)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

Any ideas...?

[akarnokd]

Please check your application for the use of Observable.unsafeCreate or extends Observable as possible candidates.

[ivnsch]

I haven't any of these... (I'm also 110% sure as I developed the app from scratch and don't even know how to use them. I did a text search anyway).

Maybe com.jakewharton.rxbinding2:rxbinding-kotlin:2.0.0 could be responsible? I see some of them there and it's the only dependency that could be causing this.

[akarnokd]

My guess is this line in the Rx binding. If you subscribe off the main thread, the error path doesn't properly initialize the stream and you get an NPE.

[ivnsch]

I think I'm doing all my UI operations using the main thread scheduler, but will review.

Anyway, how can I debug to confirm this (if possible not having to put breakpoints in rxbinding-kotlin)? The exception you linked to is nowhere to be seen in the stacktrace...

[akarnokd]

Place a breakpoint on that method.

/cc @JakeWharton

[ivnsch]

heh, I just edited my last comment with "if possible not having to put breakpoints in rxbinding-kotlin"... I'll do it... but am curious in general how to debug this kind of things. I mean, if you weren't helping me I wouldn't have an idea about where to put the breakpoint...

[akarnokd]

This is the trouble with omitting an onSubscribe in a sequence that goes async. I'd modify one of the debug support implementation with protocol verification.

[ivnsch]

@akarnokd Ok, I got it, I forgot to use the main thread scheduler in a call, which at some point calls rx bindings. It's triggered in the line you linked to. I found this using the breakpoint - enabling debug support didn't have an apparent effect and the stacktrace was the same as before... probably I need to dive more into it to understand how to use it.

[akarnokd]

I've posted the issue on RxBinding. I'll also think about adding some additional debug support in RxJava2Extensions to help detecting such cases.

[ivnsch]

Thanks!