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.Collection;
  import java.util.Objects;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Supplier;
  import io.reactivex.rxjava3.internal.queue.MpscLinkedQueue;
  import io.reactivex.rxjava3.internal.subscribers.QueueDrainSubscriber;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.internal.util.QueueDrainHelper;
  import io.reactivex.rxjava3.subscribers.*;
  
  public final class FlowableBufferExactBoundary<T, U extends Collection<? super T>, B>
  extends AbstractFlowableWithUpstream<T, U> {
      final Publisher<B> boundary;
      final Supplier<U> bufferSupplier;
  
      public FlowableBufferExactBoundary(Flowable<T> source, Publisher<B> boundary, Supplier<U> bufferSupplier) {
          super(source);
          this.boundary = boundary;
          this.bufferSupplier = bufferSupplier;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super U> s) {
          source.subscribe(new BufferExactBoundarySubscriber<>(new SerializedSubscriber<>(s), bufferSupplier, boundary));
      }
  
      static final class BufferExactBoundarySubscriber<T, U extends Collection<? super T>, B>
      extends QueueDrainSubscriber<T, U, U> implements Subscription, Disposable {
  
          final Supplier<U> bufferSupplier;
          final Publisher<B> boundary;
  
          Subscription upstream;
  
          Disposable other;
  
          U buffer;
  
          BufferExactBoundarySubscriber(Subscriber<? super U> actual, Supplier<U> bufferSupplier,
                                               Publisher<B> boundary) {
              super(actual, new MpscLinkedQueue<>());
              this.bufferSupplier = bufferSupplier;
              this.boundary = boundary;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (!SubscriptionHelper.validate(this.upstream, s)) {
                  return;
              }
              this.upstream = s;
  
              U b;
  
              try {
                  b = Objects.requireNonNull(bufferSupplier.get(), "The buffer supplied is null");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  cancelled = true;
                  s.cancel();
                  EmptySubscription.error(e, downstream);
                  return;
              }
  
              buffer = b;
  
              BufferBoundarySubscriber<T, U, B> bs = new BufferBoundarySubscriber<>(this);
              other = bs;
  
              downstream.onSubscribe(this);
  
              if (!cancelled) {
                  s.request(Long.MAX_VALUE);
  
                  boundary.subscribe(bs);
              }
          }
  
          @Override
          public void onNext(T t) {
              synchronized (this) {
                  U b = buffer;
                  if (b == null) {
                      return;
                  }
                  b.add(t);
              }
          }
  
          @Override
          public void onError(Throwable t) {
              cancel();
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              U b;
              synchronized (this) {
                  b = buffer;
                  if (b == null) {
                      return;
                  }
                  buffer = null;
              }
              queue.offer(b);
              done = true;
              if (enter()) {
                  QueueDrainHelper.drainMaxLoop(queue, downstream, false, this, this);
              }
          }
  
          @Override
          public void request(long n) {
              requested(n);
          }
  
          @Override
          public void cancel() {
              if (!cancelled) {
                  cancelled = true;
                  other.dispose();
                  upstream.cancel();
  
                  if (enter()) {
                      queue.clear();
                  }
              }
          }
  
          void next() {
  
              U next;
  
              try {
                  next = Objects.requireNonNull(bufferSupplier.get(), "The buffer supplied is null");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  cancel();
                  downstream.onError(e);
                  return;
              }
  
              U b;
              synchronized (this) {
                  b = buffer;
                  if (b == null) {
                      return;
                  }
                  buffer = next;
              }
  
              fastPathEmitMax(b, false, this);
          }
  
          @Override
          public void dispose() {
              cancel();
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          @Override
          public boolean accept(Subscriber<? super U> a, U v) {
              downstream.onNext(v);
              return true;
          }
  
      }
  
      static final class BufferBoundarySubscriber<T, U extends Collection<? super T>, B> extends DisposableSubscriber<B> {
          final BufferExactBoundarySubscriber<T, U, B> parent;
  
          BufferBoundarySubscriber(BufferExactBoundarySubscriber<T, U, B> parent) {
              this.parent = parent;
          }
  
          @Override
          public void onNext(B t) {
              parent.next();
          }
  
          @Override
          public void onError(Throwable t) {
              parent.onError(t);
          }
  
          @Override
          public void onComplete() {
              parent.onComplete();
          }
      }
  }
  