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.concurrent.atomic.AtomicLong;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.annotations.Nullable;
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  import io.reactivex.rxjava3.operators.*;
  
  public final class FlowableOnBackpressureBuffer<T> extends AbstractFlowableWithUpstream<T, T> {
      final int bufferSize;
      final boolean unbounded;
      final boolean delayError;
      final Action onOverflow;
      final Consumer<? super T> onDropped;
  
      public FlowableOnBackpressureBuffer(Flowable<T> source, int bufferSize, boolean unbounded,
              boolean delayError, Action onOverflow, Consumer<? super T> onDropped) {
          super(source);
          this.bufferSize = bufferSize;
          this.unbounded = unbounded;
          this.delayError = delayError;
          this.onOverflow = onOverflow;
          this.onDropped = onDropped;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
          source.subscribe(new BackpressureBufferSubscriber<>(s, bufferSize, unbounded, delayError, onOverflow, onDropped));
      }
  
      static final class BackpressureBufferSubscriber<T> extends BasicIntQueueSubscription<T> implements FlowableSubscriber<T> {
  
          private static final long serialVersionUID = -2514538129242366402L;
  
          final Subscriber<? super T> downstream;
          final SimplePlainQueue<T> queue;
          final boolean delayError;
          final Action onOverflow;
          final Consumer<? super T> onDropped;
  
          Subscription upstream;
  
          volatile boolean cancelled;
  
          volatile boolean done;
          Throwable error;
  
          final AtomicLong requested = new AtomicLong();
  
          boolean outputFused;
  
          BackpressureBufferSubscriber(Subscriber<? super T> actual, int bufferSize,
                  boolean unbounded, boolean delayError, Action onOverflow, Consumer<? super T> onDropped) {
              this.downstream = actual;
              this.onOverflow = onOverflow;
              this.delayError = delayError;
              this.onDropped = onDropped;
  
              SimplePlainQueue<T> q;
  
              if (unbounded) {
                  q = new SpscLinkedArrayQueue<>(bufferSize);
              } else {
                  q = new SpscArrayQueue<>(bufferSize);
              }
  
              this.queue = q;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
                  downstream.onSubscribe(this);
                  s.request(Long.MAX_VALUE);
              }
          }
  
          @Override
          public void onNext(T t) {
              if (!queue.offer(t)) {
                  upstream.cancel();
                  MissingBackpressureException ex = new MissingBackpressureException("Buffer is full");
                  try {
                      onOverflow.run();
                      onDropped.accept(t);
                  } catch (Throwable e) {
                      Exceptions.throwIfFatal(e);
                      ex.initCause(e);
                  }
                  onError(ex);
                  return;
              }
              if (outputFused) {
                  downstream.onNext(null);
              } else {
                  drain();
              }
          }
  
          @Override
          public void onError(Throwable t) {
              error = t;
              done = true;
              if (outputFused) {
                  downstream.onError(t);
              } else {
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              done = true;
              if (outputFused) {
                  downstream.onComplete();
              } else {
                  drain();
              }
          }
  
          @Override
          public void request(long n) {
              if (!outputFused) {
                  if (SubscriptionHelper.validate(n)) {
                      BackpressureHelper.add(requested, n);
                      drain();
                  }
              }
          }
  
          @Override
          public void cancel() {
              if (!cancelled) {
                  cancelled = true;
                  upstream.cancel();
  
                  if (!outputFused && getAndIncrement() == 0) {
                      queue.clear();
                  }
              }
          }
  
          void drain() {
              if (getAndIncrement() == 0) {
                  int missed = 1;
                  final SimplePlainQueue<T> q = queue;
                  final Subscriber<? super T> a = downstream;
                  for (;;) {
  
                      if (checkTerminated(done, q.isEmpty(), a)) {
                          return;
                      }
  
                      long r = requested.get();
  
                      long e = 0L;
  
                      while (e != r) {
                          boolean d = done;
                          T v = q.poll();
                          boolean empty = v == null;
  
                          if (checkTerminated(d, empty, a)) {
                              return;
                          }
  
                          if (empty) {
                              break;
                          }
  
                          a.onNext(v);
  
                          e++;
                      }
  
                      if (e == r) {
                          boolean d = done;
                          boolean empty = q.isEmpty();
  
                          if (checkTerminated(d, empty, a)) {
                              return;
                          }
                      }
  
                      if (e != 0L) {
                          if (r != Long.MAX_VALUE) {
                              requested.addAndGet(-e);
                          }
                      }
  
                      missed = addAndGet(-missed);
                      if (missed == 0) {
                          break;
                      }
                  }
              }
          }
  
          boolean checkTerminated(boolean d, boolean empty, Subscriber<? super T> a) {
              if (cancelled) {
                  queue.clear();
                  return true;
              }
              if (d) {
                  if (delayError) {
                      if (empty) {
                          Throwable e = error;
                          if (e != null) {
                              a.onError(e);
                          } else {
                              a.onComplete();
                          }
                          return true;
                      }
                  } else {
                      Throwable e = error;
                      if (e != null) {
                          queue.clear();
                          a.onError(e);
                          return true;
                      } else
                      if (empty) {
                          a.onComplete();
                          return true;
                      }
                  }
              }
              return false;
          }
  
          @Override
          public int requestFusion(int mode) {
              if ((mode & ASYNC) != 0) {
                  outputFused = true;
                  return ASYNC;
              }
              return NONE;
          }
  
          @Nullable
          @Override
          public T poll() {
              return queue.poll();
          }
  
          @Override
          public void clear() {
              queue.clear();
          }
  
          @Override
          public boolean isEmpty() {
              return queue.isEmpty();
          }
      }
  }
  