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.flowable;
  
  import java.util.*;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.AtomicLong;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.Flowable;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  
  /**
   * Creates {@link Flowable} of a number of items followed by either an error or
   * completion. Cancellation has no effect on preventing emissions until the
   * currently outstanding requests have been met.
   * @param <T> the value type
   */
  public final class Burst<T> extends Flowable<T> {
  
      final List<T> items;
      final Throwable error;
  
      Burst(Throwable error, List<T> items) {
          if (items.isEmpty()) {
              throw new IllegalArgumentException("items cannot be empty");
          }
          for (T item : items) {
              if (item == null) {
                  throw new IllegalArgumentException("items cannot include null");
              }
          }
          this.error = error;
          this.items = items;
      }
  
      @Override
      protected void subscribeActual(final Subscriber<? super T> subscriber) {
          subscriber.onSubscribe(new BurstSubscription(subscriber));
  
      }
  
      public static <T> Builder<T> item(T item) {
          return items(item);
      }
  
      @SafeVarargs
      public static <T> Builder<T> items(T... items) {
          return new Builder<>(Arrays.asList(items));
      }
  
      final class BurstSubscription implements Subscription {
          private final Subscriber<? super T> subscriber;
          final Queue<T> q = new ConcurrentLinkedQueue<>(items);
          final AtomicLong requested = new AtomicLong();
          volatile boolean cancelled;
  
          BurstSubscription(Subscriber<? super T> subscriber) {
              this.subscriber = subscriber;
          }
  
          @Override
          public void request(long n) {
              if (cancelled) {
                  // required by reactive-streams-jvm 3.6
                  return;
              }
              if (SubscriptionHelper.validate(n)) {
                  // just for testing, don't care about perf
                  // so no attempt made to reduce volatile reads
                  if (BackpressureHelper.add(requested, n) == 0) {
                      if (q.isEmpty()) {
                          return;
                      }
                      while (!q.isEmpty() && requested.get() > 0) {
                          T item = q.poll();
                          requested.decrementAndGet();
                          subscriber.onNext(item);
                      }
                      if (q.isEmpty()) {
                          if (error != null) {
                              subscriber.onError(error);
                          } else {
                              subscriber.onComplete();
                          }
                      }
                  }
              }
          }
  
          @Override
          public void cancel() {
              cancelled = true;
          }
      }
  
      public static final class Builder<T> {
  
          private final List<T> items;
          private Throwable error;
  
          Builder(List<T> items) {
              this.items = items;
          }
  
          public Flowable<T> error(Throwable e) {
              this.error = e;
              return create();
          }
  
          public Flowable<T> create() {
              return new Burst<>(error, items);
          }
  
      }
  
  }
  