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.flowable;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.*;
  import io.reactivex.rxjava3.operators.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class FlowableFlatMap<T, U> extends AbstractFlowableWithUpstream<T, U> {
      final Function<? super T, ? extends Publisher<? extends U>> mapper;
      final boolean delayErrors;
      final int maxConcurrency;
      final int bufferSize;
  
      public FlowableFlatMap(Flowable<T> source,
              Function<? super T, ? extends Publisher<? extends U>> mapper,
              boolean delayErrors, int maxConcurrency, int bufferSize) {
          super(source);
          this.mapper = mapper;
          this.delayErrors = delayErrors;
          this.maxConcurrency = maxConcurrency;
          this.bufferSize = bufferSize;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super U> s) {
          if (FlowableScalarXMap.tryScalarXMapSubscribe(source, s, mapper)) {
              return;
          }
          source.subscribe(subscribe(s, mapper, delayErrors, maxConcurrency, bufferSize));
      }
  
      public static <T, U> FlowableSubscriber<T> subscribe(Subscriber<? super U> s,
              Function<? super T, ? extends Publisher<? extends U>> mapper,
              boolean delayErrors, int maxConcurrency, int bufferSize) {
          return new MergeSubscriber<>(s, mapper, delayErrors, maxConcurrency, bufferSize);
      }
  
      static final class MergeSubscriber<T, U> extends AtomicInteger implements FlowableSubscriber<T>, Subscription {
  
          private static final long serialVersionUID = -2117620485640801370L;
  
          final Subscriber<? super U> downstream;
          final Function<? super T, ? extends Publisher<? 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 cancelled;
  
          final AtomicReference<InnerSubscriber<?, ?>[]> subscribers = new AtomicReference<>();
  
          static final InnerSubscriber<?, ?>[] EMPTY = new InnerSubscriber<?, ?>[0];
  
          static final InnerSubscriber<?, ?>[] CANCELLED = new InnerSubscriber<?, ?>[0];
  
          final AtomicLong requested = new AtomicLong();
  
          Subscription upstream;
  
          long uniqueId;
          long lastId;
          int lastIndex;
  
          int scalarEmitted;
          final int scalarLimit;
  
          MergeSubscriber(Subscriber<? super U> actual, Function<? super T, ? extends Publisher<? extends U>> mapper,
                  boolean delayErrors, int maxConcurrency, int bufferSize) {
              this.downstream = actual;
              this.mapper = mapper;
              this.delayErrors = delayErrors;
              this.maxConcurrency = maxConcurrency;
              this.bufferSize = bufferSize;
              this.scalarLimit = Math.max(1, maxConcurrency >> 1);
              subscribers.lazySet(EMPTY);
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
                  downstream.onSubscribe(this);
                  if (!cancelled) {
                      if (maxConcurrency == Integer.MAX_VALUE) {
                          s.request(Long.MAX_VALUE);
                      } else {
                          s.request(maxConcurrency);
                      }
                  }
              }
          }
  
          @SuppressWarnings("unchecked")
          @Override
          public void onNext(T t) {
              // safeguard against misbehaving sources
              if (done) {
                  return;
              }
              Publisher<? extends U> p;
              try {
                  p = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null Publisher");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  upstream.cancel();
                  onError(e);
                  return;
              }
              if (p instanceof Supplier) {
                  U u;
  
                  try {
                      u  = ((Supplier<U>)p).get();
                  } catch (Throwable ex) {
                      Exceptions.throwIfFatal(ex);
                      errors.tryAddThrowableOrReport(ex);
                      drain();
                      return;
                  }
  
                  if (u != null) {
                      tryEmitScalar(u);
                  } else {
                      if (maxConcurrency != Integer.MAX_VALUE
                              && !cancelled && ++scalarEmitted == scalarLimit) {
                          scalarEmitted = 0;
                          upstream.request(scalarLimit);
                      }
                  }
              } else {
                  InnerSubscriber<T, U> inner = new InnerSubscriber<>(this, bufferSize, uniqueId++);
                  if (addInner(inner)) {
                      p.subscribe(inner);
                  }
              }
          }
  
          boolean addInner(InnerSubscriber<T, U> inner) {
              for (;;) {
                  InnerSubscriber<?, ?>[] a = subscribers.get();
                  if (a == CANCELLED) {
                      inner.dispose();
                      return false;
                  }
                  int n = a.length;
                  InnerSubscriber<?, ?>[] b = new InnerSubscriber[n + 1];
                  System.arraycopy(a, 0, b, 0, n);
                  b[n] = inner;
                  if (subscribers.compareAndSet(a, b)) {
                      return true;
                  }
              }
          }
  
          void removeInner(InnerSubscriber<T, U> inner) {
              for (;;) {
                  InnerSubscriber<?, ?>[] a = subscribers.get();
                  int n = a.length;
                  if (n == 0) {
                      return;
                  }
                  int j = -1;
                  for (int i = 0; i < n; i++) {
                      if (a[i] == inner) {
                          j = i;
                          break;
                      }
                  }
                  if (j < 0) {
                      return;
                  }
                  InnerSubscriber<?, ?>[] b;
                  if (n == 1) {
                      b = EMPTY;
                  } else {
                      b = new InnerSubscriber<?, ?>[n - 1];
                      System.arraycopy(a, 0, b, 0, j);
                      System.arraycopy(a, j + 1, b, j, n - j - 1);
                  }
                  if (subscribers.compareAndSet(a, b)) {
                      return;
                  }
              }
          }
  
          SimpleQueue<U> getMainQueue() {
              SimplePlainQueue<U> q = queue;
              if (q == null) {
                  if (maxConcurrency == Integer.MAX_VALUE) {
                      q = new SpscLinkedArrayQueue<>(bufferSize);
                  } else {
                      q = new SpscArrayQueue<>(maxConcurrency);
                  }
                  queue = q;
              }
              return q;
          }
  
          void tryEmitScalar(U value) {
              if (get() == 0 && compareAndSet(0, 1)) {
                  long r = requested.get();
                  SimpleQueue<U> q = queue;
                  if (r != 0L && (q == null || q.isEmpty())) {
                      downstream.onNext(value);
                      if (r != Long.MAX_VALUE) {
                          requested.decrementAndGet();
                      }
                      if (maxConcurrency != Integer.MAX_VALUE
                              && !cancelled && ++scalarEmitted == scalarLimit) {
                          scalarEmitted = 0;
                          upstream.request(scalarLimit);
                      }
                  } else {
                      if (q == null) {
                          q = getMainQueue();
                      }
                      if (!q.offer(value)) {
                          onError(new QueueOverflowException());
                      }
                  }
                  if (decrementAndGet() == 0) {
                      return;
                  }
              } else {
                  SimpleQueue<U> q = getMainQueue();
                  if (!q.offer(value)) {
                      onError(new QueueOverflowException());
                      return;
                  }
                  if (getAndIncrement() != 0) {
                      return;
                  }
              }
              drainLoop();
          }
  
          void tryEmit(U value, InnerSubscriber<T, U> inner) {
              if (get() == 0 && compareAndSet(0, 1)) {
                  long r = requested.get();
                  SimpleQueue<U> q = inner.queue;
                  if (r != 0L && (q == null || q.isEmpty())) {
                      downstream.onNext(value);
                      if (r != Long.MAX_VALUE) {
                          requested.decrementAndGet();
                      }
                      inner.requestMore(1);
                  } else {
                      if (q == null) {
                          q = new SpscArrayQueue<>(bufferSize);
                          inner.queue = q;
                      }
                      if (!q.offer(value)) {
                          onError(new QueueOverflowException());
                      }
                  }
                  if (decrementAndGet() == 0) {
                      return;
                  }
              } else {
                  SimpleQueue<U> q = inner.queue;
                  if (q == null) {
                      q = new SpscArrayQueue<>(bufferSize);
                      inner.queue = q;
                  }
                  if (!q.offer(value)) {
                      onError(new QueueOverflowException());
                      return;
                  }
                  if (getAndIncrement() != 0) {
                      return;
                  }
              }
              drainLoop();
          }
  
          @Override
          public void onError(Throwable t) {
              // safeguard against misbehaving sources
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              if (errors.tryAddThrowableOrReport(t)) {
                  done = true;
                  if (!delayErrors) {
                      for (InnerSubscriber<?, ?> a : subscribers.getAndSet(CANCELLED)) {
                          a.dispose();
                      }
                  }
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              // safeguard against misbehaving sources
              if (done) {
                  return;
              }
              done = true;
              drain();
          }
  
          @Override
          public void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(requested, n);
                  drain();
              }
          }
  
          @Override
          public void cancel() {
              if (!cancelled) {
                  cancelled = true;
                  upstream.cancel();
                  disposeAll();
                  if (getAndIncrement() == 0) {
                      SimpleQueue<U> q = queue;
                      if (q != null) {
                          q.clear();
                      }
                  }
              }
          }
  
          void drain() {
              if (getAndIncrement() == 0) {
                  drainLoop();
              }
          }
  
          void drainLoop() {
              final Subscriber<? super U> child = this.downstream;
              int missed = 1;
              for (;;) {
                  if (checkTerminate()) {
                      return;
                  }
                  SimplePlainQueue<U> svq = queue;
  
                  long r = requested.get();
                  boolean unbounded = r == Long.MAX_VALUE;
  
                  long replenishMain = 0;
  
                  if (svq != null) {
                      long scalarEmission = 0;
                      U o = null;
                      while (r != 0L) {
                          o = svq.poll();
  
                          if (checkTerminate()) {
                              return;
                          }
                          if (o == null) {
                              break;
                          }
  
                          child.onNext(o);
  
                          replenishMain++;
                          scalarEmission++;
                          r--;
                      }
                      if (scalarEmission != 0L) {
                          if (unbounded) {
                              r = Long.MAX_VALUE;
                          } else {
                              r = requested.addAndGet(-scalarEmission);
                          }
                      }
                  }
  
                  boolean d = done;
                  svq = queue;
                  InnerSubscriber<?, ?>[] inner = subscribers.get();
                  int n = inner.length;
  
                  if (d && (svq == null || svq.isEmpty()) && n == 0) {
                      errors.tryTerminateConsumer(downstream);
                      return;
                  }
  
                  boolean innerCompleted = false;
                  if (n != 0) {
                      long startId = lastId;
                      int index = lastIndex;
  
                      if (n <= index || inner[index].id != startId) {
                          if (n <= index) {
                              index = 0;
                          }
                          int j = index;
                          for (int i = 0; i < n; i++) {
                              if (inner[j].id == startId) {
                                  break;
                              }
                              j++;
                              if (j == n) {
                                  j = 0;
                              }
                          }
                          index = j;
                          lastIndex = j;
                          lastId = inner[j].id;
                      }
  
                      int j = index;
                      sourceLoop:
                      for (int i = 0; i < n; i++) {
                          if (checkTerminate()) {
                              return;
                          }
  
                          @SuppressWarnings("unchecked")
                          InnerSubscriber<T, U> is = (InnerSubscriber<T, U>)inner[j];
  
                          U o = null;
                          for (;;) {
                              SimpleQueue<U> q = is.queue;
                              if (q == null) {
                                  break;
                              }
                              long produced = 0;
                              while (r != 0L) {
                                  if (checkTerminate()) {
                                      return;
                                  }
  
                                  try {
                                      o = q.poll();
                                  } catch (Throwable ex) {
                                      Exceptions.throwIfFatal(ex);
                                      is.dispose();
                                      errors.tryAddThrowableOrReport(ex);
                                      if (!delayErrors) {
                                          upstream.cancel();
                                      }
                                      if (checkTerminate()) {
                                          return;
                                      }
                                      removeInner(is);
                                      innerCompleted = true;
                                      i++;
                                      continue sourceLoop;
                                  }
                                  if (o == null) {
                                      break;
                                  }
  
                                  child.onNext(o);
  
                                  r--;
                                  produced++;
                              }
                              if (produced != 0L) {
                                  if (!unbounded) {
                                      r = requested.addAndGet(-produced);
                                  } else {
                                      r = Long.MAX_VALUE;
                                  }
                                  is.requestMore(produced);
                              }
                              if (r == 0 || o == null) {
                                  break;
                              }
                          }
                          boolean innerDone = is.done;
                          SimpleQueue<U> innerQueue = is.queue;
                          if (innerDone && (innerQueue == null || innerQueue.isEmpty())) {
                              removeInner(is);
                              if (checkTerminate()) {
                                  return;
                              }
                              replenishMain++;
                              innerCompleted = true;
                          }
                          if (r == 0L) {
                              break;
                          }
  
                          j++;
                          if (j == n) {
                              j = 0;
                          }
                      }
                      lastIndex = j;
                      lastId = inner[j].id;
                  }
  
                  if (replenishMain != 0L && !cancelled) {
                      upstream.request(replenishMain);
                  }
                  if (innerCompleted) {
                      continue;
                  }
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          boolean checkTerminate() {
              if (cancelled) {
                  clearScalarQueue();
                  return true;
              }
              if (!delayErrors && errors.get() != null) {
                  clearScalarQueue();
                  errors.tryTerminateConsumer(downstream);
                  return true;
              }
              return false;
          }
  
          void clearScalarQueue() {
              SimpleQueue<U> q = queue;
              if (q != null) {
                  q.clear();
              }
          }
  
          void disposeAll() {
              InnerSubscriber<?, ?>[] a = subscribers.getAndSet(CANCELLED);
              if (a != CANCELLED) {
                  for (InnerSubscriber<?, ?> inner : a) {
                      inner.dispose();
                  }
                  errors.tryTerminateAndReport();
              }
          }
  
          void innerError(InnerSubscriber<T, U> inner, Throwable t) {
              if (errors.tryAddThrowableOrReport(t)) {
                  inner.done = true;
                  if (!delayErrors) {
                      upstream.cancel();
                      for (InnerSubscriber<?, ?> a : subscribers.getAndSet(CANCELLED)) {
                          a.dispose();
                      }
                  }
                  drain();
              }
          }
      }
  
      static final class InnerSubscriber<T, U> extends AtomicReference<Subscription>
      implements FlowableSubscriber<U>, Disposable {
  
          private static final long serialVersionUID = -4606175640614850599L;
          final long id;
          final MergeSubscriber<T, U> parent;
          final int limit;
          final int bufferSize;
  
          volatile boolean done;
          volatile SimpleQueue<U> queue;
          long produced;
          int fusionMode;
  
          InnerSubscriber(MergeSubscriber<T, U> parent, int bufferSize, long id) {
              this.id = id;
              this.parent = parent;
              this.bufferSize = bufferSize;
              this.limit = bufferSize >> 2;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.setOnce(this, s)) {
  
                  if (s instanceof QueueSubscription) {
                      @SuppressWarnings("unchecked")
                      QueueSubscription<U> qs = (QueueSubscription<U>) s;
                      int m = qs.requestFusion(QueueSubscription.ANY | QueueSubscription.BOUNDARY);
                      if (m == QueueSubscription.SYNC) {
                          fusionMode = m;
                          queue = qs;
                          done = true;
                          parent.drain();
                          return;
                      }
                      if (m == QueueSubscription.ASYNC) {
                          fusionMode = m;
                          queue = qs;
                      }
  
                  }
  
                  s.request(bufferSize);
              }
          }
  
          @Override
          public void onNext(U t) {
              if (fusionMode != QueueSubscription.ASYNC) {
                  parent.tryEmit(t, this);
              } else {
                  parent.drain();
              }
          }
  
          @Override
          public void onError(Throwable t) {
              lazySet(SubscriptionHelper.CANCELLED);
              parent.innerError(this, t);
          }
  
          @Override
          public void onComplete() {
              done = true;
              parent.drain();
          }
  
          void requestMore(long n) {
              if (fusionMode != QueueSubscription.SYNC) {
                  long p = produced + n;
                  if (p >= limit) {
                      produced = 0;
                      get().request(p);
                  } else {
                      produced = p;
                  }
              }
          }
  
          @Override
          public void dispose() {
              SubscriptionHelper.cancel(this);
          }
  
          @Override
          public boolean isDisposed() {
              return get() == SubscriptionHelper.CANCELLED;
          }
      }
  }
  