RxRange.java

import java.util.concurrent.atomic.AtomicLong;

import rx.Observable.OnSubscribe;
import rx.*;
import rx.internal.operators.BackpressureUtils;

public final class RxRange implements OnSubscribe<Integer> {
    final int start;
    final int count;
    public RxRange(int start, int count) {
        if (count < 0) {
            throw new IllegalArgumentException();
        }
        this.start = start;
        this.count = count;
    }
    @Override
    public void call(Subscriber<? super Integer> t) {
        if (count == 0) {
            t.onCompleted();
            return;
        }
        RangeProducer p = new RangeProducer(t, start, count);
        t.setProducer(p);
    }
    
    public Observable<Integer> toObservable() {
        return Observable.create(this);
    }
    
    static final class RangeProducer extends AtomicLong implements Producer {
        /** */
        private static final long serialVersionUID = 5318571951669533517L;
        final Subscriber<? super Integer> child;
        int index;
        int remaining;
        public RangeProducer(Subscriber<? super Integer> child, int start, int count) {
            this.child = child;
            this.index = start;
            this.remaining = count;
        }
        @Override
        public void request(long n) {
            if (n < 0) {
                throw new IllegalArgumentException();
            }
            if (n == 0) {
                return;
            }
            if (BackpressureUtils.getAndAddRequest(this, n) != 0) {
                return;
            }
            long r = n;
            for (;;) {
                if (child.isUnsubscribed()) {
                    return;
                }
                int i = index;
                int k = remaining;
                int e = 0;
                
                while (r > 0 && k > 0) {
                    child.onNext(i);
                    if (child.isUnsubscribed()) {
                        return;
                    }
                    k--;
                    if (k == 0) {
                        child.onCompleted();
                    }
                    e++;
                    i++;
                    r--;
                }
                index = i;
                remaining = k;
                
                r = addAndGet(-e);
                
                if (r == 0) {
                    return;
                }
            }
        }
    }
    
    public static void main(String[] args) {
        Observable<Integer> range = new RxRange(1, 10).toObservable();
        
        range.take(5).subscribe(
            System.out::println,
            Throwable::printStackTrace,
            () -> System.out.println("Done")
        );
    }
}

it looks like you missed to exit the for loop in line 54 when k = 0.
something like this:
if (k == 0) {
child.onCompleted();
return;
}