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.*;
  import java.util.concurrent.atomic.*;
  
  import io.reactivex.rxjava3.core.ObservableSource;
  import io.reactivex.rxjava3.core.Observer;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.util.AtomicThrowable;
  import io.reactivex.rxjava3.operators.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class ObservableFlatMap<T, U> extends AbstractObservableWithUpstream<T, U> {
      final Function<? super T, ? extends ObservableSource<? extends U>> mapper;
      final boolean delayErrors;
      final int maxConcurrency;
      final int bufferSize;
  
      public ObservableFlatMap(ObservableSource<T> source,
              Function<? super T, ? extends ObservableSource<? extends U>> mapper,
              boolean delayErrors, int maxConcurrency, int bufferSize) {
          super(source);
          this.mapper = mapper;
          this.delayErrors = delayErrors;
          this.maxConcurrency = maxConcurrency;
          this.bufferSize = bufferSize;
      }
  
      @Override
      public void subscribeActual(Observer<? super U> t) {
  
          if (ObservableScalarXMap.tryScalarXMapSubscribe(source, t, mapper)) {
              return;
          }
  
          source.subscribe(new MergeObserver<>(t, mapper, delayErrors, maxConcurrency, bufferSize));
      }
  
      static final class MergeObserver<T, U> extends AtomicInteger implements Disposable, Observer<T> {
  
          private static final long serialVersionUID = -2117620485640801370L;
  
          final Observer<? super U> downstream;
          final Function<? super T, ? extends ObservableSource<? extends U>> mapper;
          final boolean delayErrors;
          final int maxConcurrency;
          final int bufferSize;
  
          volatile SimplePlainQueue<U> queue;
  
          volatile boolean done;
  
          final AtomicThrowable errors = new AtomicThrowable();
  
          volatile boolean disposed;
  
          final AtomicReference<InnerObserver<?, ?>[]> observers;
  
          static final InnerObserver<?, ?>[] EMPTY = new InnerObserver<?, ?>[0];
  
          static final InnerObserver<?, ?>[] CANCELLED = new InnerObserver<?, ?>[0];
  
          Disposable upstream;
  
          long uniqueId;
          int lastIndex;
  
          Queue<ObservableSource<? extends U>> sources;
  
          int wip;
  
          MergeObserver(Observer<? super U> actual, Function<? super T, ? extends ObservableSource<? extends U>> mapper,
                  boolean delayErrors, int maxConcurrency, int bufferSize) {
              this.downstream = actual;
              this.mapper = mapper;
              this.delayErrors = delayErrors;
              this.maxConcurrency = maxConcurrency;
              this.bufferSize = bufferSize;
              if (maxConcurrency != Integer.MAX_VALUE) {
                  sources = new ArrayDeque<>(maxConcurrency);
              }
              this.observers = new AtomicReference<>(EMPTY);
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T t) {
              // safeguard against misbehaving sources
              if (done) {
                  return;
              }
              ObservableSource<? extends U> p;
              try {
                  p = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null ObservableSource");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  upstream.dispose();
                  onError(e);
                  return;
              }
  
              if (maxConcurrency != Integer.MAX_VALUE) {
                  synchronized (this) {
                      if (wip == maxConcurrency) {
                          sources.offer(p);
                          return;
                      }
                      wip++;
                  }
              }
  
              subscribeInner(p);
          }
  
          @SuppressWarnings("unchecked")
          void subscribeInner(ObservableSource<? extends U> p) {
              for (;;) {
                  if (p instanceof Supplier) {
                      if (tryEmitScalar(((Supplier<? extends U>)p)) && maxConcurrency != Integer.MAX_VALUE) {
                          boolean empty = false;
                          synchronized (this) {
                              p = sources.poll();
                              if (p == null) {
                                  wip--;
                                  empty = true;
                              }
                          }
                          if (empty) {
                              drain();
                              break;
                          }
                      } else {
                          break;
                      }
                  } else {
                      InnerObserver<T, U> inner = new InnerObserver<>(this, uniqueId++);
                      if (addInner(inner)) {
                          p.subscribe(inner);
                      }
                      break;
                  }
              }
          }
  
          boolean addInner(InnerObserver<T, U> inner) {
              for (;;) {
                  InnerObserver<?, ?>[] a = observers.get();
                  if (a == CANCELLED) {
                      inner.dispose();
                      return false;
                  }
                  int n = a.length;
                  InnerObserver<?, ?>[] b = new InnerObserver[n + 1];
                  System.arraycopy(a, 0, b, 0, n);
                  b[n] = inner;
                  if (observers.compareAndSet(a, b)) {
                      return true;
                  }
              }
          }
  
          void removeInner(InnerObserver<T, U> inner) {
              for (;;) {
                  InnerObserver<?, ?>[] a = observers.get();
                  int n = a.length;
                  int j = -1;
                  for (int i = 0; i < n; i++) {
                      if (a[i] == inner) {
                          j = i;
                          break;
                      }
                  }
                  if (j < 0) {
                      return;
                  }
                  InnerObserver<?, ?>[] b;
                  if (n == 1) {
                      b = EMPTY;
                  } else {
                      b = new InnerObserver<?, ?>[n - 1];
                      System.arraycopy(a, 0, b, 0, j);
                      System.arraycopy(a, j + 1, b, j, n - j - 1);
                  }
                  if (observers.compareAndSet(a, b)) {
                      return;
                  }
              }
          }
  
          boolean tryEmitScalar(Supplier<? extends U> value) {
              U u;
              try {
                  u = value.get();
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  errors.tryAddThrowableOrReport(ex);
                  drain();
                  return true;
              }
  
              if (u == null) {
                  return true;
              }
  
              if (get() == 0 && compareAndSet(0, 1)) {
                  downstream.onNext(u);
                  if (decrementAndGet() == 0) {
                      return true;
                  }
              } else {
                  SimplePlainQueue<U> q = queue;
                  if (q == null) {
                      if (maxConcurrency == Integer.MAX_VALUE) {
                          q = new SpscLinkedArrayQueue<>(bufferSize);
                      } else {
                          q = new SpscArrayQueue<>(maxConcurrency);
                      }
                      queue = q;
                  }
  
                  q.offer(u);
                  if (getAndIncrement() != 0) {
                      return false;
                  }
              }
              drainLoop();
              return true;
          }
  
          void tryEmit(U value, InnerObserver<T, U> inner) {
              if (get() == 0 && compareAndSet(0, 1)) {
                  downstream.onNext(value);
                  if (decrementAndGet() == 0) {
                      return;
                  }
              } else {
                  SimpleQueue<U> q = inner.queue;
                  if (q == null) {
                      q = new SpscLinkedArrayQueue<>(bufferSize);
                      inner.queue = q;
                  }
                  q.offer(value);
                  if (getAndIncrement() != 0) {
                      return;
                  }
              }
              drainLoop();
          }
  
          @Override
          public void onError(Throwable t) {
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              if (errors.tryAddThrowableOrReport(t)) {
                  done = true;
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              if (done) {
                  return;
              }
              done = true;
              drain();
          }
  
          @Override
          public void dispose() {
              disposed = true;
              if (disposeAll()) {
                  errors.tryTerminateAndReport();
              }
          }
  
          @Override
          public boolean isDisposed() {
              return disposed;
          }
  
          void drain() {
              if (getAndIncrement() == 0) {
                  drainLoop();
              }
          }
  
          void drainLoop() {
              final Observer<? super U> child = this.downstream;
              int missed = 1;
              for (;;) {
                  if (checkTerminate()) {
                      return;
                  }
                  int innerCompleted = 0;
                  SimplePlainQueue<U> svq = queue;
  
                  if (svq != null) {
                      for (;;) {
                          if (checkTerminate()) {
                              return;
                          }
  
                          U o = svq.poll();
  
                          if (o == null) {
                              break;
                          }
  
                          child.onNext(o);
                          innerCompleted++;
                      }
                  }
  
                  if (innerCompleted != 0) {
                      if (maxConcurrency != Integer.MAX_VALUE) {
                          subscribeMore(innerCompleted);
                          innerCompleted = 0;
                      }
                      continue;
                  }
  
                  boolean d = done;
                  svq = queue;
                  InnerObserver<?, ?>[] inner = observers.get();
                  int n = inner.length;
  
                  int nSources = 0;
                  if (maxConcurrency != Integer.MAX_VALUE) {
                      synchronized (this) {
                          nSources = sources.size();
                      }
                  }
  
                  if (d && (svq == null || svq.isEmpty()) && n == 0 && nSources == 0) {
                      errors.tryTerminateConsumer(downstream);
                      return;
                  }
  
                  if (n != 0) {
                      int j = Math.min(n - 1, lastIndex);
  
                      sourceLoop:
                      for (int i = 0; i < n; i++) {
                          if (checkTerminate()) {
                              return;
                          }
  
                          @SuppressWarnings("unchecked")
                          InnerObserver<T, U> is = (InnerObserver<T, U>)inner[j];
                          SimpleQueue<U> q = is.queue;
                          if (q != null) {
                              for (;;) {
                                  U o;
                                  try {
                                      o = q.poll();
                                  } catch (Throwable ex) {
                                      Exceptions.throwIfFatal(ex);
                                      is.dispose();
                                      errors.tryAddThrowableOrReport(ex);
                                      if (checkTerminate()) {
                                          return;
                                      }
                                      removeInner(is);
                                      innerCompleted++;
                                      j++;
                                      if (j == n) {
                                          j = 0;
                                      }
                                      continue sourceLoop;
                                  }
                                  if (o == null) {
                                      break;
                                  }
  
                                  child.onNext(o);
  
                                  if (checkTerminate()) {
                                      return;
                                  }
                              }
                          }
  
                          boolean innerDone = is.done;
                          SimpleQueue<U> innerQueue = is.queue;
                          if (innerDone && (innerQueue == null || innerQueue.isEmpty())) {
                              removeInner(is);
                              innerCompleted++;
                          }
  
                          j++;
                          if (j == n) {
                              j = 0;
                          }
                      }
                      lastIndex = j;
                  }
  
                  if (innerCompleted != 0) {
                      if (maxConcurrency != Integer.MAX_VALUE) {
                          subscribeMore(innerCompleted);
                          innerCompleted = 0;
                      }
                      continue;
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          void subscribeMore(int innerCompleted) {
              while (innerCompleted-- != 0) {
                  ObservableSource<? extends U> p;
                  synchronized (this) {
                      p = sources.poll();
                      if (p == null) {
                          wip--;
                          continue;
                      }
                  }
                  subscribeInner(p);
              }
          }
  
          boolean checkTerminate() {
              if (disposed) {
                  return true;
              }
              Throwable e = errors.get();
              if (!delayErrors && (e != null)) {
                  disposeAll();
                  errors.tryTerminateConsumer(downstream);
                  return true;
              }
              return false;
          }
  
          boolean disposeAll() {
              upstream.dispose();
              InnerObserver<?, ?>[] a = observers.getAndSet(CANCELLED);
              if (a != CANCELLED) {
                  for (InnerObserver<?, ?> inner : a) {
                      inner.dispose();
                  }
                  return true;
              }
              return false;
          }
      }
  
      static final class InnerObserver<T, U> extends AtomicReference<Disposable>
      implements Observer<U> {
  
          private static final long serialVersionUID = -4606175640614850599L;
          final long id;
          final MergeObserver<T, U> parent;
  
          volatile boolean done;
          volatile SimpleQueue<U> queue;
  
          int fusionMode;
  
          InnerObserver(MergeObserver<T, U> parent, long id) {
              this.id = id;
              this.parent = parent;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.setOnce(this, d)) {
                  if (d instanceof QueueDisposable) {
                      @SuppressWarnings("unchecked")
                      QueueDisposable<U> qd = (QueueDisposable<U>) d;
  
                      int m = qd.requestFusion(QueueDisposable.ANY | QueueDisposable.BOUNDARY);
                      if (m == QueueDisposable.SYNC) {
                          fusionMode = m;
                          queue = qd;
                          done = true;
                          parent.drain();
                          return;
                      }
                      if (m == QueueDisposable.ASYNC) {
                          fusionMode = m;
                          queue = qd;
                      }
                  }
              }
          }
  
          @Override
          public void onNext(U t) {
              if (fusionMode == QueueDisposable.NONE) {
                  parent.tryEmit(t, this);
              } else {
                  parent.drain();
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (parent.errors.tryAddThrowableOrReport(t)) {
                  if (!parent.delayErrors) {
                      parent.disposeAll();
                  }
                  done = true;
                  parent.drain();
              }
          }
  
          @Override
          public void onComplete() {
              done = true;
              parent.drain();
          }
  
          public void dispose() {
              DisposableHelper.dispose(this);
          }
      }
  }
  