Out of Memory Error RxAndroid + RxJava + Retrofit2

Question

I am new to using RxAndroid and RxJava. I am using RxJava + Retrofit2 to make GET requests. I am doing approximately 1500 GET requests using the following code and getting Out of memory error. However the same code this time with only retrofit, NO RxAndroid and it works. So my conclusion was I am doing something wrong in RxAndroid. Can you please help with what I am missing?

Code Sample:

Subject<Story> mStoryEmitter = PublishSubject.create();

private void getStory(int storyID) {
    HNApi.Factory.getInstance().getStory(storyID).subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(getStoryObserver());
}

mStoryListEmitter.subscribe(new Observer<List<Integer>>() {
    @Override
    public void onSubscribe(Disposable d) {}

    @Override
    public void onNext(List<Integer> value) {
        if(mRecyclerView != null) {
            mRecyclerView.setAdapter(null);
            if(mAdapter != null) {
                mAdapter.clear();
                mAdapter = null;
            }
        }
        mAdapter = new SimpleRecyclerViewAdapter();
        mRecyclerView.setAdapter(mAdapter);

        for(Integer storyID : value) {
            getStory(storyID);
        }
    }

    @Override
    public void onError(Throwable e) {}

    @Override
    public void onComplete() {}
});

private DisposableObserver<Story> getStoryObserver() {
    DisposableObserver<Story> observer = new DisposableObserver<Story>() {
        @Override
        public void onNext(Story value) {
            mStoryEmitter.onNext(value);
            dispose();
        }

        @Override
        public void onError(Throwable e) {

        }

        @Override
        public void onComplete() {

        }
    };
    return observer;
}

Error:

    Throwing OutOfMemoryError "Could not allocate JNI Env"
java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.
    at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:111)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
 Caused by: java.lang.OutOfMemoryError: Could not allocate JNI Env
    at java.lang.Thread.nativeCreate(Native Method)
    at java.lang.Thread.start(Thread.java:1063)
    at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:921)
    at java.util.concurrent.ThreadPoolExecutor.ensurePrestart(ThreadPoolExecutor.java:1556)
    at java.util.concurrent.ScheduledThreadPoolExecutor.delayedExecute(ScheduledThreadPoolExecutor.java:310)
    at java.util.concurrent.ScheduledThreadPoolExecutor.schedule(ScheduledThreadPoolExecutor.java:543)
    at java.util.concurrent.ScheduledThreadPoolExecutor.submit(ScheduledThreadPoolExecutor.java:642)
    at io.reactivex.internal.schedulers.NewThreadWorker.scheduleActual(NewThreadWorker.java:120)
    at io.reactivex.internal.schedulers.IoScheduler$EventLoopWorker.schedule(IoScheduler.java:221)
    at io.reactivex.Scheduler.scheduleDirect(Scheduler.java:130)
    at io.reactivex.Scheduler.scheduleDirect(Scheduler.java:109)
 AppData::create pipe(2) failed: Too many open files
    at io.reactivex.internal.operators.observable.ObservableSubscribeOn.subscribeActual(ObservableSubscribeOn.java:36)
    at io.reactivex.Observable.subscribe(Observable.java:10514)
    at io.reactivex.internal.operators.observable.ObservableObserveOn.subscribeActual(ObservableObserveOn.java:44)
    at io.reactivex.Observable.subscribe(Observable.java:10514)
    at com.example.MainActivity.getStory(MainActivity.java:100)
    at com.example.MainActivity.access$300(MainActivity.java:25)
    at com.example.MainActivity$2.onNext(MainActivity.java:67)
    at com.example.MainActivity$2.onNext(MainActivity.java:49)
    at io.reactivex.subjects.PublishSubject$PublishDisposable.onNext(PublishSubject.java:263)
    at io.reactivex.subjects.PublishSubject.onNext(PublishSubject.java:182)
    at com.example.MainActivity$5.onNext(MainActivity.java:147)
    at com.example.MainActivity$5.onNext(MainActivity.java:138)
    at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.drainNormal(ObservableObserveOn.java:198)
    at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.run(ObservableObserveOn.java:250)
    at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:109)
    ... 7 more
 AppData::create pipe(2) failed: Too many open files
 FATAL EXCEPTION: main
 Process: com.example, PID: 15857
 java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.
    at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:111)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
 Caused by: java.lang.OutOfMemoryError: Could not allocate JNI Env
    at java.lang.Thread.nativeCreate(Native Method)
    at java.lang.Thread.start(Thread.java:1063)
    at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:921)
    at java.util.concurrent.ThreadPoolExecutor.ensurePrestart(ThreadPoolExecutor.java:1556)
    at java.util.concurrent.ScheduledThreadPoolExecutor.delayedExecute(ScheduledThreadPoolExecutor.java:310)
    at java.util.concurrent.ScheduledThreadPoolExecutor.schedule(ScheduledThreadPoolExecutor.java:543)
    at java.util.concurrent.ScheduledThreadPoolExecutor.submit(ScheduledThreadPoolExecutor.java:642)
    at io.reactivex.internal.schedulers.NewThreadWorker.scheduleActual(NewThreadWorker.java:120)
    at io.reactivex.internal.schedulers.IoScheduler$EventLoopWorker.schedule(IoScheduler.java:221)
    at io.reactivex.Scheduler.scheduleDirect(Scheduler.java:130)
    at io.reactivex.Scheduler.scheduleDirect(Scheduler.java:109)
    at io.reactivex.internal.operators.observable.ObservableSubscribeOn.subscribeActual(ObservableSubscribeOn.java:36)
    at io.reactivex.Observable.subscribe(Observable.java:10514)
    at io.reactivex.internal.operators.observable.ObservableObserveOn.subscribeActual(ObservableObserveOn.java:44)
    at io.reactivex.Observable.subscribe(Observable.java:10514)
    at com.example.MainActivity.getStory(MainActivity.java:100)
    at com.example.MainActivity.access$300(MainActivity.java:25)
    at com.example.MainActivity$2.onNext(MainActivity.java:67)
    at com.example.MainActivity$2.onNext(MainActivity.java:49)
    at io.reactivex.subjects.PublishSubject$PublishDisposable.onNext(PublishSubject.java:263)
    at io.reactivex.subjects.PublishSubject.onNext(PublishSubject.java:182)
    at com.example.MainActivity$5.onNext(MainActivity.java:147)
    at com.example.MainActivity$5.onNext(MainActivity.java:138)
    at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.drainNormal(ObservableObserveOn.java:198)
    at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.run(ObservableObserveOn.java:250)
    at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:109)
    ... 7 more

Answer 1

Posted the same question at RxAndroid github.

And JakeWharton reply acually heped

The problem is that Schedulers.io() uses a cached thread pool without a limit and thus is trying to create 1500 threads. You should consider using a Scheduler that has a fixed limit of threads, or using RxJava 2.x's parallel() operator to parallelize the operation to a fixed number of workers.

If you're using raw Retrofit by default it uses OkHttp's dispatcher which limits the threads to something like 64 (with a max of 5 per host). That's why you aren't seeing it fail.

If you use createAsync() when creating the RxJava2CallAdapterFactory it will create fully-async Observable instances that don't require a subscribeOn and which use OkHttp's Dispatcher just like Retrofit would otherwise. Then you only need observeOn to move back to the main thread, and you avoid all additional thread creation.