NetworkOnMainThread RxJava + Retrofit + Lollipop+

Question

I'm getting reports of a NetworkOnMainThread exception on Lollipop+ when running an https api call using Retrofit and RxAndroid.

I have isolated the code and created the following example that still fails.

Here's the build.gradle:

apply plugin: 'com.android.application'
apply plugin: 'me.tatarka.retrolambda'

android {
  compileSdkVersion 23
  buildToolsVersion "23.0.1"

  defaultConfig {
    applicationId "com.example.bug"
    minSdkVersion 9
    targetSdkVersion 23
    versionCode 1
    versionName "1.0"
  }
  buildTypes {
    release {
      minifyEnabled false
      proguardFiles getDefaultProguardFile('proguard-android.txt')
    }
  }
  lintOptions {
    abortOnError false
  }
  compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
  }
}

dependencies {
  compile fileTree(dir: 'libs', include: ['*.jar'])
  testCompile 'junit:junit:4.12'
  compile 'com.android.support:appcompat-v7:23.0.1'

  compile 'com.squareup.okhttp:okhttp:2.5.0'
  compile 'com.squareup.okhttp:okhttp-urlconnection:2.5.0'
  compile 'com.squareup.retrofit:adapter-rxjava:2.0.0-beta2'
  compile 'com.squareup.retrofit:converter-gson:2.0.0-beta2'
  compile 'com.squareup.retrofit:retrofit:2.0.0-beta2'
  compile 'io.reactivex:rxandroid:1.0.1'
}

Here's the sole activity:

public class HomeActivity extends Activity {

  private static final String URL_BASE = "https://some.https.api.com/";
  private static final String ENDPOINT = "some/endpoint";

  @Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    OkHttpClient okHttpClient = new OkHttpClient();
    okHttpClient.setConnectTimeout(15, TimeUnit.SECONDS);
    okHttpClient.setReadTimeout(15, TimeUnit.SECONDS);

    Retrofit retrofit = new Retrofit.Builder()
        .baseUrl(URL_BASE)
        .client(okHttpClient)
        .addConverterFactory(GsonConverterFactory.create(new Gson()))
        .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
        .build();

    MyApi mService = retrofit.create(MyApi.class);

    setContentView(R.layout.home_activity);
    Button button = (Button) findViewById(R.id.button);
    button.setOnClickListener(v->
        mService.whatever(new ParamObject())
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(
                response -> Log.d("BUG", response.status),
                error -> Log.d("BUG", error.toString()))
    );
  }

  interface MyApi {

    @POST(ENDPOINT)
    Observable<ResponseObject> whatever( @Body ParamObject requirements);
  }

  class ResponseObject {
    public String status;
  }

  class ParamObject {
  }
}

Here's the exception stacktrace:

E/AndroidRuntime(28345): FATAL EXCEPTION: main
E/AndroidRuntime(28345): Process: com.example.bug, PID: 28345
E/AndroidRuntime(28345): java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.Worker thread.
E/AndroidRuntime(28345):    at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:62)
E/AndroidRuntime(28345):    at android.os.Handler.handleCallback(Handler.java:739)
E/AndroidRuntime(28345):    at android.os.Handler.dispatchMessage(Handler.java:95)
E/AndroidRuntime(28345):    at android.os.Looper.loop(Looper.java:135)
E/AndroidRuntime(28345):    at android.app.ActivityThread.main(ActivityThread.java:5221)
E/AndroidRuntime(28345):    at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime(28345):    at java.lang.reflect.Method.invoke(Method.java:372)
E/AndroidRuntime(28345):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
E/AndroidRuntime(28345):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
E/AndroidRuntime(28345): Caused by: android.os.NetworkOnMainThreadException
E/AndroidRuntime(28345):    at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1147)
E/AndroidRuntime(28345):    at com.android.org.conscrypt.OpenSSLSocketImpl$SSLOutputStream.write(OpenSSLSocketImpl.java:724)
E/AndroidRuntime(28345):    at okio.Okio$1.write(Okio.java:80)
E/AndroidRuntime(28345):    at okio.AsyncTimeout$1.write(AsyncTimeout.java:155)
E/AndroidRuntime(28345):    at okio.RealBufferedSink.flush(RealBufferedSink.java:221)
E/AndroidRuntime(28345):    at com.squareup.okhttp.internal.framed.Http2$Writer.rstStream(Http2.java:475)
E/AndroidRuntime(28345):    at com.squareup.okhttp.internal.framed.FramedConnection.writeSynReset(FramedConnection.java:356)
E/AndroidRuntime(28345):    at com.squareup.okhttp.internal.framed.FramedStream.close(FramedStream.java:222)
E/AndroidRuntime(28345):    at com.squareup.okhttp.internal.http.FramedTransport.disconnect(FramedTransport.java:215)
E/AndroidRuntime(28345):    at com.squareup.okhttp.internal.http.HttpEngine.disconnect(HttpEngine.java:573)
E/AndroidRuntime(28345):    at com.squareup.okhttp.Call.cancel(Call.java:122)
E/AndroidRuntime(28345):    at retrofit.OkHttpCall.cancel(OkHttpCall.java:162)
E/AndroidRuntime(28345):    at retrofit.RxJavaCallAdapterFactory$CallOnSubscribe$1.call(RxJavaCallAdapterFactory.java:102)
E/AndroidRuntime(28345):    at rx.subscriptions.BooleanSubscription.unsubscribe(BooleanSubscription.java:72)
E/AndroidRuntime(28345):    at rx.internal.util.SubscriptionList.unsubscribeFromAll(SubscriptionList.java:124)
E/AndroidRuntime(28345):    at rx.internal.util.SubscriptionList.unsubscribe(SubscriptionList.java:113)
E/AndroidRuntime(28345):    at rx.Subscriber.unsubscribe(Subscriber.java:98)
E/AndroidRuntime(28345):    at rx.internal.util.SubscriptionList.unsubscribeFromAll(SubscriptionList.java:124)
E/AndroidRuntime(28345):    at rx.internal.util.SubscriptionList.unsubscribe(SubscriptionList.java:113)
E/AndroidRuntime(28345):    at rx.Subscriber.unsubscribe(Subscriber.java:98)
E/AndroidRuntime(28345):    at rx.internal.util.SubscriptionList.unsubscribeFromAll(SubscriptionList.java:124)
E/AndroidRuntime(28345):    at rx.internal.util.SubscriptionList.unsubscribe(SubscriptionList.java:113)
E/AndroidRuntime(28345):    at rx.Subscriber.unsubscribe(Subscriber.java:98)
E/AndroidRuntime(28345):    at rx.observers.SafeSubscriber.onCompleted(SafeSubscriber.java:90)
E/AndroidRuntime(28345):    at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.pollQueue(OperatorObserveOn.java:201)
E/AndroidRuntime(28345):    at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber$2.call(OperatorObserveOn.java:170)
E/AndroidRuntime(28345):    at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
E/AndroidRuntime(28345):    ... 8 more

A few things:

• This code example works just fine in Android 4.x
• I have tried this example (with minor changes) against the GitHub API and it works just fine.
• The API is running on Google's app engine.
• Note that the observable is being subscribe on Schedulers.io() and observed on AndroidSchedulers.mainThread()

Any ideas?

Edit

• After taking a closer look at the stacktrace I figure there was something about http2. Although not the same issue reported here, the following line to restrict the OkHttp available protocols made it work again.

  okHttpClient.setProtocols(Collections.singletonList(Protocol.HTTP_1_1));

Answer 1

It's a known bug in OkHttp that canceling a call does I/O on the canceling thread. Will be fixed in a future release.

Answer 2

Until this issue has been fixed add unsubscribeOn(Schedulers.io()) to the RX call chain. See this commit for an example if you need some more context.