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.ArrayDeque;
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.observers.*;
  import io.reactivex.rxjava3.internal.util.*;
  import io.reactivex.rxjava3.operators.QueueDisposable;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  import io.reactivex.rxjava3.operators.SpscLinkedArrayQueue;
  
  public final class ObservableConcatMapEager<T, R> extends AbstractObservableWithUpstream<T, R> {
  
      final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
  
      final ErrorMode errorMode;
  
      final int maxConcurrency;
  
      final int prefetch;
  
      public ObservableConcatMapEager(ObservableSource<T> source,
              Function<? super T, ? extends ObservableSource<? extends R>> mapper,
              ErrorMode errorMode,
              int maxConcurrency, int prefetch) {
          super(source);
          this.mapper = mapper;
          this.errorMode = errorMode;
          this.maxConcurrency = maxConcurrency;
          this.prefetch = prefetch;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          source.subscribe(new ConcatMapEagerMainObserver<>(observer, mapper, maxConcurrency, prefetch, errorMode));
      }
  
      static final class ConcatMapEagerMainObserver<T, R>
      extends AtomicInteger
      implements Observer<T>, Disposable, InnerQueuedObserverSupport<R> {
  
          private static final long serialVersionUID = 8080567949447303262L;
  
          final Observer<? super R> downstream;
  
          final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
  
          final int maxConcurrency;
  
          final int prefetch;
  
          final ErrorMode errorMode;
  
          final AtomicThrowable errors;
  
          final ArrayDeque<InnerQueuedObserver<R>> observers;
  
          SimpleQueue<T> queue;
  
          Disposable upstream;
  
          volatile boolean done;
  
          int sourceMode;
  
          volatile boolean cancelled;
  
          InnerQueuedObserver<R> current;
  
          int activeCount;
  
          ConcatMapEagerMainObserver(Observer<? super R> actual,
                  Function<? super T, ? extends ObservableSource<? extends R>> mapper,
                  int maxConcurrency, int prefetch, ErrorMode errorMode) {
              this.downstream = actual;
              this.mapper = mapper;
              this.maxConcurrency = maxConcurrency;
              this.prefetch = prefetch;
              this.errorMode = errorMode;
              this.errors = new AtomicThrowable();
              this.observers = new ArrayDeque<>();
          }
  
          @SuppressWarnings("unchecked")
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  if (d instanceof QueueDisposable) {
                      QueueDisposable<T> qd = (QueueDisposable<T>) d;
  
                      int m = qd.requestFusion(QueueDisposable.ANY);
                      if (m == QueueDisposable.SYNC) {
                          sourceMode = m;
                          queue = qd;
                          done = true;
  
                          downstream.onSubscribe(this);
  
                          drain();
                          return;
                      }
                      if (m == QueueDisposable.ASYNC) {
                          sourceMode = m;
                          queue = qd;
  
                          downstream.onSubscribe(this);
  
                          return;
                      }
                  }
  
                  queue = new SpscLinkedArrayQueue<>(prefetch);
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T value) {
              if (sourceMode == QueueDisposable.NONE) {
                  queue.offer(value);
              }
              drain();
          }
  
          @Override
          public void onError(Throwable e) {
              if (errors.tryAddThrowableOrReport(e)) {
                  done = true;
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              done = true;
              drain();
          }
  
          @Override
          public void dispose() {
              if (cancelled) {
                  return;
              }
              cancelled = true;
              upstream.dispose();
              errors.tryTerminateAndReport();
  
              drainAndDispose();
          }
  
          void drainAndDispose() {
              if (getAndIncrement() == 0) {
                  do {
                      queue.clear();
                      disposeAll();
                  } while (decrementAndGet() != 0);
              }
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          void disposeAll() {
              InnerQueuedObserver<R> inner = current;
  
              if (inner != null) {
                  inner.dispose();
              }
  
              for (;;) {
  
                  inner = observers.poll();
  
                  if (inner == null) {
                      return;
                  }
  
                  inner.dispose();
              }
          }
  
          @Override
          public void innerNext(InnerQueuedObserver<R> inner, R value) {
              inner.queue().offer(value);
              drain();
          }
  
          @Override
          public void innerError(InnerQueuedObserver<R> inner, Throwable e) {
              if (errors.tryAddThrowableOrReport(e)) {
                  if (errorMode == ErrorMode.IMMEDIATE) {
                      upstream.dispose();
                  }
                  inner.setDone();
                  drain();
              }
          }
  
          @Override
          public void innerComplete(InnerQueuedObserver<R> inner) {
              inner.setDone();
              drain();
          }
  
          @Override
          public void drain() {
              if (getAndIncrement() != 0) {
                  return;
              }
  
              int missed = 1;
  
              SimpleQueue<T> q = queue;
              ArrayDeque<InnerQueuedObserver<R>> observers = this.observers;
              Observer<? super R> a = this.downstream;
              ErrorMode errorMode = this.errorMode;
  
              outer:
              for (;;) {
  
                  int ac = activeCount;
  
                  while (ac != maxConcurrency) {
                      if (cancelled) {
                          q.clear();
                          disposeAll();
                          return;
                      }
  
                      if (errorMode == ErrorMode.IMMEDIATE) {
                          Throwable ex = errors.get();
                          if (ex != null) {
                              q.clear();
                              disposeAll();
  
                              errors.tryTerminateConsumer(downstream);
                              return;
                          }
                      }
  
                      T v;
                      ObservableSource<? extends R> source;
  
                      try {
                          v = q.poll();
  
                          if (v == null) {
                              break;
                          }
  
                          source = Objects.requireNonNull(mapper.apply(v), "The mapper returned a null ObservableSource");
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          upstream.dispose();
                          q.clear();
                          disposeAll();
                          errors.tryAddThrowableOrReport(ex);
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
  
                      InnerQueuedObserver<R> inner = new InnerQueuedObserver<>(this, prefetch);
  
                      observers.offer(inner);
  
                      source.subscribe(inner);
  
                      ac++;
                  }
  
                  activeCount = ac;
  
                  if (cancelled) {
                      q.clear();
                      disposeAll();
                      return;
                  }
  
                  if (errorMode == ErrorMode.IMMEDIATE) {
                      Throwable ex = errors.get();
                      if (ex != null) {
                          q.clear();
                          disposeAll();
  
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
                  }
  
                  InnerQueuedObserver<R> active = current;
  
                  if (active == null) {
                      if (errorMode == ErrorMode.BOUNDARY) {
                          Throwable ex = errors.get();
                          if (ex != null) {
                              q.clear();
                              disposeAll();
  
                              errors.tryTerminateConsumer(a);
                              return;
                          }
                      }
                      boolean d = done;
  
                      active = observers.poll();
  
                      boolean empty = active == null;
  
                      if (d && empty) {
                          Throwable ex = errors.get();
                          if (ex != null) {
                              q.clear();
                              disposeAll();
  
                              errors.tryTerminateConsumer(a);
                          } else {
                              a.onComplete();
                          }
                          return;
                      }
  
                      if (!empty) {
                          current = active;
                      }
  
                  }
  
                  if (active != null) {
                      SimpleQueue<R> aq = active.queue();
  
                      for (;;) {
                          if (cancelled) {
                              q.clear();
                              disposeAll();
                              return;
                          }
  
                          boolean d = active.isDone();
  
                          if (errorMode == ErrorMode.IMMEDIATE) {
                              Throwable ex = errors.get();
                              if (ex != null) {
                                  q.clear();
                                  disposeAll();
  
                                  errors.tryTerminateConsumer(a);
                                  return;
                              }
                          }
  
                          R w;
  
                          try {
                              w = aq.poll();
                          } catch (Throwable ex) {
                              Exceptions.throwIfFatal(ex);
                              errors.tryAddThrowableOrReport(ex);
  
                              current = null;
                              activeCount--;
                              continue outer;
                          }
  
                          boolean empty = w == null;
  
                          if (d && empty) {
                              current = null;
                              activeCount--;
                              continue outer;
                          }
  
                          if (empty) {
                              break;
                          }
  
                          a.onNext(w);
                      }
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
      }
  
  }
  