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.Collection;
  import java.util.Objects;
  
  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.disposables.*;
  import io.reactivex.rxjava3.internal.observers.QueueDrainObserver;
  import io.reactivex.rxjava3.internal.queue.MpscLinkedQueue;
  import io.reactivex.rxjava3.internal.util.QueueDrainHelper;
  import io.reactivex.rxjava3.observers.*;
  
  public final class ObservableBufferExactBoundary<T, U extends Collection<? super T>, B>
  extends AbstractObservableWithUpstream<T, U> {
      final ObservableSource<B> boundary;
      final Supplier<U> bufferSupplier;
  
      public ObservableBufferExactBoundary(ObservableSource<T> source, ObservableSource<B> boundary, Supplier<U> bufferSupplier) {
          super(source);
          this.boundary = boundary;
          this.bufferSupplier = bufferSupplier;
      }
  
      @Override
      protected void subscribeActual(Observer<? super U> t) {
          source.subscribe(new BufferExactBoundaryObserver<>(new SerializedObserver<>(t), bufferSupplier, boundary));
      }
  
      static final class BufferExactBoundaryObserver<T, U extends Collection<? super T>, B>
      extends QueueDrainObserver<T, U, U> implements Disposable {
  
          final Supplier<U> bufferSupplier;
          final ObservableSource<B> boundary;
  
          Disposable upstream;
  
          Disposable other;
  
          U buffer;
  
          BufferExactBoundaryObserver(Observer<? super U> actual, Supplier<U> bufferSupplier,
                                               ObservableSource<B> boundary) {
              super(actual, new MpscLinkedQueue<>());
              this.bufferSupplier = bufferSupplier;
              this.boundary = boundary;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  U b;
  
                  try {
                      b = Objects.requireNonNull(bufferSupplier.get(), "The buffer supplied is null");
                  } catch (Throwable e) {
                      Exceptions.throwIfFatal(e);
                      cancelled = true;
                      d.dispose();
                      EmptyDisposable.error(e, downstream);
                      return;
                  }
  
                  buffer = b;
  
                  BufferBoundaryObserver<T, U, B> bs = new BufferBoundaryObserver<>(this);
                  other = bs;
  
                  downstream.onSubscribe(this);
  
                  if (!cancelled) {
                      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) {
              dispose();
              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.drainLoop(queue, downstream, false, this, this);
              }
          }
  
          @Override
          public void dispose() {
              if (!cancelled) {
                  cancelled = true;
                  other.dispose();
                  upstream.dispose();
  
                  if (enter()) {
                      queue.clear();
                  }
              }
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          void next() {
  
              U next;
  
              try {
                  next = Objects.requireNonNull(bufferSupplier.get(), "The buffer supplied is null");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  dispose();
                  downstream.onError(e);
                  return;
              }
  
              U b;
              synchronized (this) {
                  b = buffer;
                  if (b == null) {
                      return;
                  }
                  buffer = next;
              }
  
              fastPathEmit(b, false, this);
          }
  
          @Override
          public void accept(Observer<? super U> a, U v) {
              downstream.onNext(v);
          }
  
      }
  
      static final class BufferBoundaryObserver<T, U extends Collection<? super T>, B>
      extends DisposableObserver<B> {
          final BufferExactBoundaryObserver<T, U, B> parent;
  
          BufferBoundaryObserver(BufferExactBoundaryObserver<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();
          }
      }
  }
  