code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.operators.observable;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.BiFunction;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.observers.SerializedObserver;
  
  public final class ObservableWithLatestFrom<T, U, R> extends AbstractObservableWithUpstream<T, R> {
      final BiFunction<? super T, ? super U, ? extends R> combiner;
      final ObservableSource<? extends U> other;
      public ObservableWithLatestFrom(ObservableSource<T> source,
              BiFunction<? super T, ? super U, ? extends R> combiner, ObservableSource<? extends U> other) {
          super(source);
          this.combiner = combiner;
          this.other = other;
      }
  
      @Override
      public void subscribeActual(Observer<? super R> t) {
          final SerializedObserver<R> serial = new SerializedObserver<>(t);
          final WithLatestFromObserver<T, U, R> wlf = new WithLatestFromObserver<>(serial, combiner);
  
          serial.onSubscribe(wlf);
  
          other.subscribe(new WithLatestFromOtherObserver(wlf));
  
          source.subscribe(wlf);
      }
  
      static final class WithLatestFromObserver<T, U, R> extends AtomicReference<U> implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = -312246233408980075L;
  
          final Observer<? super R> downstream;
  
          final BiFunction<? super T, ? super U, ? extends R> combiner;
  
          final AtomicReference<Disposable> upstream = new AtomicReference<>();
  
          final AtomicReference<Disposable> other = new AtomicReference<>();
  
          WithLatestFromObserver(Observer<? super R> actual, BiFunction<? super T, ? super U, ? extends R> combiner) {
              this.downstream = actual;
              this.combiner = combiner;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              DisposableHelper.setOnce(this.upstream, d);
          }
  
          @Override
          public void onNext(T t) {
              U u = get();
              if (u != null) {
                  R r;
                  try {
                      r = Objects.requireNonNull(combiner.apply(t, u), "The combiner returned a null value");
                  } catch (Throwable e) {
                      Exceptions.throwIfFatal(e);
                      dispose();
                      downstream.onError(e);
                      return;
                  }
                  downstream.onNext(r);
              }
          }
  
          @Override
          public void onError(Throwable t) {
              DisposableHelper.dispose(other);
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              DisposableHelper.dispose(other);
              downstream.onComplete();
          }
  
          @Override
          public void dispose() {
              DisposableHelper.dispose(upstream);
              DisposableHelper.dispose(other);
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(upstream.get());
          }
  
          public boolean setOther(Disposable o) {
              return DisposableHelper.setOnce(other, o);
          }
  
          public void otherError(Throwable e) {
              DisposableHelper.dispose(upstream);
              downstream.onError(e);
          }
      }
  
      final class WithLatestFromOtherObserver implements Observer<U> {
          private final WithLatestFromObserver<T, U, R> parent;
  
          WithLatestFromOtherObserver(WithLatestFromObserver<T, U, R> parent) {
              this.parent = parent;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              parent.setOther(d);
          }
  
          @Override
          public void onNext(U t) {
              parent.lazySet(t);
          }
  
          @Override
          public void onError(Throwable t) {
              parent.otherError(t);
          }
  
          @Override
          public void onComplete() {
              // nothing to do, the wlf will complete on its own pace
          }
      }
  }
  