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.maybe;
  
  import java.util.Objects;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.Subscriber;
  
  import io.reactivex.rxjava3.annotations.Nullable;
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.*;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.internal.util.*;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  
  /**
   * Run all MaybeSources of an array at once and signal their values as they become available.
   *
   * @param <T> the value type
   */
  public final class MaybeMergeArray<T> extends Flowable<T> {
  
      final MaybeSource<? extends T>[] sources;
  
      public MaybeMergeArray(MaybeSource<? extends T>[] sources) {
          this.sources = sources;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
          MaybeSource<? extends T>[] maybes = sources;
          int n = maybes.length;
  
          SimpleQueueWithConsumerIndex<Object> queue;
  
          if (n <= bufferSize()) {
              queue = new MpscFillOnceSimpleQueue<>(n);
          } else {
              queue = new ClqSimpleQueue<>();
          }
          MergeMaybeObserver<T> parent = new MergeMaybeObserver<>(s, n, queue);
  
          s.onSubscribe(parent);
  
          AtomicThrowable e = parent.errors;
  
          for (MaybeSource<? extends T> source : maybes) {
              if (parent.isCancelled() || e.get() != null) {
                  return;
              }
  
              source.subscribe(parent);
          }
      }
  
      static final class MergeMaybeObserver<T>
      extends BasicIntQueueSubscription<T> implements MaybeObserver<T> {
  
          private static final long serialVersionUID = -660395290758764731L;
  
          final Subscriber<? super T> downstream;
  
          final CompositeDisposable set;
  
          final AtomicLong requested;
  
          final SimpleQueueWithConsumerIndex<Object> queue;
  
          final AtomicThrowable errors;
  
          final int sourceCount;
  
          volatile boolean cancelled;
  
          boolean outputFused;
  
          long consumed;
  
          MergeMaybeObserver(Subscriber<? super T> actual, int sourceCount, SimpleQueueWithConsumerIndex<Object> queue) {
              this.downstream = actual;
              this.sourceCount = sourceCount;
              this.set = new CompositeDisposable();
              this.requested = new AtomicLong();
              this.errors = new AtomicThrowable();
              this.queue = queue;
          }
  
          @Override
          public int requestFusion(int mode) {
              if ((mode & ASYNC) != 0) {
                  outputFused = true;
                  return ASYNC;
              }
              return NONE;
          }
  
          @Nullable
          @SuppressWarnings("unchecked")
          @Override
          public T poll() {
              for (;;) {
                  Object o = queue.poll();
                  if (o != NotificationLite.COMPLETE) {
                      return (T)o;
                  }
              }
          }
  
          @Override
          public boolean isEmpty() {
              return queue.isEmpty();
          }
  
          @Override
          public void clear() {
              queue.clear();
          }
  
          @Override
          public void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(requested, n);
                  drain();
              }
          }
  
          @Override
          public void cancel() {
              if (!cancelled) {
                  cancelled = true;
                  set.dispose();
                  if (getAndIncrement() == 0) {
                      queue.clear();
                  }
              }
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              set.add(d);
          }
  
          @Override
          public void onSuccess(T value) {
              queue.offer(value);
              drain();
          }
  
          @Override
          public void onError(Throwable e) {
              if (errors.tryAddThrowableOrReport(e)) {
                  set.dispose();
                  queue.offer(NotificationLite.COMPLETE);
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              queue.offer(NotificationLite.COMPLETE);
              drain();
          }
  
          boolean isCancelled() {
              return cancelled;
          }
  
          @SuppressWarnings("unchecked")
          void drainNormal() {
              int missed = 1;
              Subscriber<? super T> a = downstream;
              SimpleQueueWithConsumerIndex<Object> q = queue;
              long e = consumed;
  
              for (;;) {
  
                  long r = requested.get();
  
                  while (e != r) {
                      if (cancelled) {
                          q.clear();
                          return;
                      }
  
                      Throwable ex = errors.get();
                      if (ex != null) {
                          q.clear();
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
  
                      if (q.consumerIndex() == sourceCount) {
                          a.onComplete();
                          return;
                      }
  
                      Object v = q.poll();
  
                      if (v == null) {
                          break;
                      }
  
                      if (v != NotificationLite.COMPLETE) {
                          a.onNext((T)v);
  
                          e++;
                      }
                  }
  
                  if (e == r) {
                      Throwable ex = errors.get();
                      if (ex != null) {
                          q.clear();
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
  
                      while (q.peek() == NotificationLite.COMPLETE) {
                          q.drop();
                      }
  
                      if (q.consumerIndex() == sourceCount) {
                          a.onComplete();
                          return;
                      }
                  }
  
                  consumed = e;
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
  
          }
  
          void drainFused() {
              int missed = 1;
              Subscriber<? super T> a = downstream;
              SimpleQueueWithConsumerIndex<Object> q = queue;
  
              for (;;) {
                  if (cancelled) {
                      q.clear();
                      return;
                  }
                  Throwable ex = errors.get();
                  if (ex != null) {
                      q.clear();
                      a.onError(ex);
                      return;
                  }
  
                  boolean d = q.producerIndex() == sourceCount;
  
                  if (!q.isEmpty()) {
                      a.onNext(null);
                  }
  
                  if (d) {
                      a.onComplete();
                      return;
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
  
          }
  
          void drain() {
              if (getAndIncrement() != 0) {
                  return;
              }
  
              if (outputFused) {
                  drainFused();
              } else {
                  drainNormal();
              }
          }
      }
  
      interface SimpleQueueWithConsumerIndex<T> extends SimpleQueue<T> {
  
          @Nullable
          @Override
          T poll();
  
          T peek();
  
          void drop();
  
          int consumerIndex();
  
          int producerIndex();
      }
  
      static final class MpscFillOnceSimpleQueue<T>
      extends AtomicReferenceArray<T>
      implements SimpleQueueWithConsumerIndex<T> {
  
          private static final long serialVersionUID = -7969063454040569579L;
          final AtomicInteger producerIndex;
  
          int consumerIndex;
  
          MpscFillOnceSimpleQueue(int length) {
              super(length);
              this.producerIndex = new AtomicInteger();
          }
  
          @Override
          public boolean offer(T value) {
              Objects.requireNonNull(value, "value is null");
              int idx = producerIndex.getAndIncrement();
              if (idx < length()) {
                  lazySet(idx, value);
                  return true;
              }
              return false;
          }
  
          @Override
          public boolean offer(T v1, T v2) {
              throw new UnsupportedOperationException();
          }
  
          @Nullable
          @Override
          public T poll() {
              int ci = consumerIndex;
              if (ci == length()) {
                  return null;
              }
              AtomicInteger pi = producerIndex;
              for (;;) {
                  T v = get(ci);
                  if (v != null) {
                      consumerIndex = ci + 1;
                      lazySet(ci, null);
                      return v;
                  }
                  if (pi.get() == ci) {
                      return null;
                  }
              }
          }
  
          @Override
          public T peek() {
              int ci = consumerIndex;
              if (ci == length()) {
                  return null;
              }
              return get(ci);
          }
  
          @Override
          public void drop() {
              int ci = consumerIndex;
              lazySet(ci, null);
              consumerIndex = ci + 1;
          }
  
          @Override
          public boolean isEmpty() {
              return consumerIndex == producerIndex();
          }
  
          @Override
          public void clear() {
              while (poll() != null && !isEmpty()) { }
          }
  
          @Override
          public int consumerIndex() {
              return consumerIndex;
          }
  
          @Override
          public int producerIndex() {
              return producerIndex.get();
          }
      }
  
      static final class ClqSimpleQueue<T> extends ConcurrentLinkedQueue<T> implements SimpleQueueWithConsumerIndex<T> {
  
          private static final long serialVersionUID = -4025173261791142821L;
  
          int consumerIndex;
  
          final AtomicInteger producerIndex;
  
          ClqSimpleQueue() {
              this.producerIndex = new AtomicInteger();
          }
  
          @Override
          public boolean offer(T v1, T v2) {
              throw new UnsupportedOperationException();
          }
  
          @Override
          public boolean offer(T e) {
              producerIndex.getAndIncrement();
              return super.offer(e);
          }
  
          @Nullable
          @Override
          public T poll() {
              T v = super.poll();
              if (v != null) {
                  consumerIndex++;
              }
              return v;
          }
  
          @Override
          public int consumerIndex() {
              return consumerIndex;
          }
  
          @Override
          public int producerIndex() {
              return producerIndex.get();
          }
  
          @Override
          public void drop() {
              poll();
          }
      }
  }
  