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.core.Scheduler.Worker;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  import io.reactivex.rxjava3.operators.ConditionalSubscriber;
  import io.reactivex.rxjava3.operators.QueueSubscription;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  import io.reactivex.rxjava3.operators.SpscArrayQueue;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {
  final Scheduler scheduler;
  
      final boolean delayError;
  
      final int prefetch;
  
      public FlowableObserveOn(
              Flowable<T> source,
              Scheduler scheduler,
              boolean delayError,
              int prefetch) {
          super(source);
          this.scheduler = scheduler;
          this.delayError = delayError;
          this.prefetch = prefetch;
      }
  
      @Override
      public void subscribeActual(Subscriber<? super T> s) {
          Worker worker = scheduler.createWorker();
  
          if (s instanceof ConditionalSubscriber) {
              source.subscribe(new ObserveOnConditionalSubscriber<>(
                      (ConditionalSubscriber<? super T>) s, worker, delayError, prefetch));
          } else {
              source.subscribe(new ObserveOnSubscriber<>(s, worker, delayError, prefetch));
          }
      }
  
      abstract static class BaseObserveOnSubscriber<T>
      extends BasicIntQueueSubscription<T>
      implements FlowableSubscriber<T>, Runnable {
          private static final long serialVersionUID = -8241002408341274697L;
  
          final Worker worker;
  
          final boolean delayError;
  
          final int prefetch;
  
          final int limit;
  
          final AtomicLong requested;
  
          Subscription upstream;
  
          SimpleQueue<T> queue;
  
          volatile boolean cancelled;
  
          volatile boolean done;
  
          Throwable error;
  
          int sourceMode;
  
          long produced;
  
          boolean outputFused;
  
          BaseObserveOnSubscriber(
                  Worker worker,
                  boolean delayError,
                  int prefetch) {
              this.worker = worker;
              this.delayError = delayError;
              this.prefetch = prefetch;
              this.requested = new AtomicLong();
              this.limit = prefetch - (prefetch >> 2);
          }
  
          @Override
          public final void onNext(T t) {
              if (done) {
                  return;
              }
              if (sourceMode == ASYNC) {
                  trySchedule();
                  return;
              }
              if (!queue.offer(t)) {
                  upstream.cancel();
  
                  error = new QueueOverflowException();
                  done = true;
              }
              trySchedule();
          }
  
          @Override
          public final void onError(Throwable t) {
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              error = t;
              done = true;
              trySchedule();
          }
  
          @Override
          public final void onComplete() {
              if (!done) {
                  done = true;
                  trySchedule();
              }
          }
  
          @Override
          public final void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(requested, n);
                  trySchedule();
              }
          }
  
          @Override
          public final void cancel() {
              if (cancelled) {
                  return;
              }
  
              cancelled = true;
              upstream.cancel();
              worker.dispose();
  
              if (!outputFused && getAndIncrement() == 0) {
                  queue.clear();
              }
          }
  
          final void trySchedule() {
              if (getAndIncrement() != 0) {
                  return;
              }
              worker.schedule(this);
          }
  
          @Override
          public final void run() {
              if (outputFused) {
                  runBackfused();
              } else if (sourceMode == SYNC) {
                  runSync();
              } else {
                  runAsync();
              }
          }
  
          abstract void runBackfused();
  
          abstract void runSync();
  
          abstract void runAsync();
  
          final boolean checkTerminated(boolean d, boolean empty, Subscriber<?> a) {
              if (cancelled) {
                  clear();
                  return true;
              }
              if (d) {
                  if (delayError) {
                      if (empty) {
                          cancelled = true;
                          Throwable e = error;
                          if (e != null) {
                              a.onError(e);
                          } else {
                              a.onComplete();
                          }
                          worker.dispose();
                          return true;
                      }
                  } else {
                      Throwable e = error;
                      if (e != null) {
                          cancelled = true;
                          clear();
                          a.onError(e);
                          worker.dispose();
                          return true;
                      } else
                      if (empty) {
                          cancelled = true;
                          a.onComplete();
                          worker.dispose();
                          return true;
                      }
                  }
              }
  
              return false;
          }
  
          @Override
          public final int requestFusion(int requestedMode) {
              if ((requestedMode & ASYNC) != 0) {
                  outputFused = true;
                  return ASYNC;
              }
              return NONE;
          }
  
          @Override
          public final void clear() {
              queue.clear();
          }
  
          @Override
          public final boolean isEmpty() {
              return queue.isEmpty();
          }
      }
  
      static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T> {
  
          private static final long serialVersionUID = -4547113800637756442L;
  
          final Subscriber<? super T> downstream;
  
          ObserveOnSubscriber(
                  Subscriber<? super T> actual,
                  Worker worker,
                  boolean delayError,
                  int prefetch) {
              super(worker, delayError, prefetch);
              this.downstream = actual;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
  
                  if (s instanceof QueueSubscription) {
                      @SuppressWarnings("unchecked")
                      QueueSubscription<T> f = (QueueSubscription<T>) s;
  
                      int m = f.requestFusion(ANY | BOUNDARY);
  
                      if (m == SYNC) {
                          sourceMode = SYNC;
                          queue = f;
                          done = true;
  
                          downstream.onSubscribe(this);
                          return;
                      } else
                      if (m == ASYNC) {
                          sourceMode = ASYNC;
                          queue = f;
  
                          downstream.onSubscribe(this);
  
                          s.request(prefetch);
  
                          return;
                      }
                  }
  
                  queue = new SpscArrayQueue<>(prefetch);
  
                  downstream.onSubscribe(this);
  
                  s.request(prefetch);
              }
          }
  
          @Override
          void runSync() {
              int missed = 1;
  
              final Subscriber<? super T> a = downstream;
              final SimpleQueue<T> q = queue;
  
              long e = produced;
  
              for (;;) {
  
                  long r = requested.get();
  
                  while (e != r) {
                      T v;
  
                      try {
                          v = q.poll();
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          cancelled = true;
                          upstream.cancel();
                          a.onError(ex);
                          worker.dispose();
                          return;
                      }
  
                      if (cancelled) {
                          return;
                      }
                      if (v == null) {
                          cancelled = true;
                          a.onComplete();
                          worker.dispose();
                          return;
                      }
  
                      a.onNext(v);
  
                      e++;
                  }
  
                  if (cancelled) {
                      return;
                  }
  
                  if (q.isEmpty()) {
                      cancelled = true;
                      a.onComplete();
                      worker.dispose();
                      return;
                  }
  
                  produced = e;
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          @Override
          void runAsync() {
              int missed = 1;
  
              final Subscriber<? super T> a = downstream;
              final SimpleQueue<T> q = queue;
  
              long e = produced;
  
              for (;;) {
  
                  long r = requested.get();
  
                  while (e != r) {
                      boolean d = done;
                      T v;
  
                      try {
                          v = q.poll();
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
  
                          cancelled = true;
                          upstream.cancel();
                          q.clear();
  
                          a.onError(ex);
                          worker.dispose();
                          return;
                      }
  
                      boolean empty = v == null;
  
                      if (checkTerminated(d, empty, a)) {
                          return;
                      }
  
                      if (empty) {
                          break;
                      }
  
                      a.onNext(v);
  
                      e++;
                      if (e == limit) {
                          if (r != Long.MAX_VALUE) {
                              r = requested.addAndGet(-e);
                          }
                          upstream.request(e);
                          e = 0L;
                      }
                  }
  
                  if (e == r && checkTerminated(done, q.isEmpty(), a)) {
                      return;
                  }
  
                  int w = get();
                  if (missed == w) {
                      produced = e;
                      missed = addAndGet(-missed);
                      if (missed == 0) {
                          break;
                      }
                  } else {
                      missed = w;
                  }
              }
          }
  
          @Override
          void runBackfused() {
              int missed = 1;
  
              for (;;) {
  
                  if (cancelled) {
                      return;
                  }
  
                  boolean d = done;
  
                  downstream.onNext(null);
  
                  if (d) {
                      cancelled = true;
                      Throwable e = error;
                      if (e != null) {
                          downstream.onError(e);
                      } else {
                          downstream.onComplete();
                      }
                      worker.dispose();
                      return;
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          @Nullable
          @Override
          public T poll() throws Throwable {
              T v = queue.poll();
              if (v != null && sourceMode != SYNC) {
                  long p = produced + 1;
                  if (p == limit) {
                      produced = 0;
                      upstream.request(p);
                  } else {
                      produced = p;
                  }
              }
              return v;
          }
  
      }
  
      static final class ObserveOnConditionalSubscriber<T>
      extends BaseObserveOnSubscriber<T> {
  
          private static final long serialVersionUID = 644624475404284533L;
  
          final ConditionalSubscriber<? super T> downstream;
  
          long consumed;
  
          ObserveOnConditionalSubscriber(
                  ConditionalSubscriber<? super T> actual,
                  Worker worker,
                  boolean delayError,
                  int prefetch) {
              super(worker, delayError, prefetch);
              this.downstream = actual;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
  
                  if (s instanceof QueueSubscription) {
                      @SuppressWarnings("unchecked")
                      QueueSubscription<T> f = (QueueSubscription<T>) s;
  
                      int m = f.requestFusion(ANY | BOUNDARY);
  
                      if (m == SYNC) {
                          sourceMode = SYNC;
                          queue = f;
                          done = true;
  
                          downstream.onSubscribe(this);
                          return;
                      } else
                      if (m == ASYNC) {
                          sourceMode = ASYNC;
                          queue = f;
  
                          downstream.onSubscribe(this);
  
                          s.request(prefetch);
  
                          return;
                      }
                  }
  
                  queue = new SpscArrayQueue<>(prefetch);
  
                  downstream.onSubscribe(this);
  
                  s.request(prefetch);
              }
          }
  
          @Override
          void runSync() {
              int missed = 1;
  
              final ConditionalSubscriber<? super T> a = downstream;
              final SimpleQueue<T> q = queue;
  
              long e = produced;
  
              for (;;) {
  
                  long r = requested.get();
  
                  while (e != r) {
                      T v;
                      try {
                          v = q.poll();
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          cancelled = true;
                          upstream.cancel();
                          a.onError(ex);
                          worker.dispose();
                          return;
                      }
  
                      if (cancelled) {
                          return;
                      }
                      if (v == null) {
                          cancelled = true;
                          a.onComplete();
                          worker.dispose();
                          return;
                      }
  
                      if (a.tryOnNext(v)) {
                          e++;
                      }
                  }
  
                  if (cancelled) {
                      return;
                  }
  
                  if (q.isEmpty()) {
                      cancelled = true;
                      a.onComplete();
                      worker.dispose();
                      return;
                  }
  
                  produced = e;
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          @Override
          void runAsync() {
              int missed = 1;
  
              final ConditionalSubscriber<? super T> a = downstream;
              final SimpleQueue<T> q = queue;
  
              long emitted = produced;
              long polled = consumed;
  
              for (;;) {
  
                  long r = requested.get();
  
                  while (emitted != r) {
                      boolean d = done;
                      T v;
                      try {
                          v = q.poll();
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
  
                          cancelled = true;
                          upstream.cancel();
                          q.clear();
  
                          a.onError(ex);
                          worker.dispose();
                          return;
                      }
                      boolean empty = v == null;
  
                      if (checkTerminated(d, empty, a)) {
                          return;
                      }
  
                      if (empty) {
                          break;
                      }
  
                      if (a.tryOnNext(v)) {
                          emitted++;
                      }
  
                      polled++;
  
                      if (polled == limit) {
                          upstream.request(polled);
                          polled = 0L;
                      }
                  }
  
                  if (emitted == r && checkTerminated(done, q.isEmpty(), a)) {
                      return;
                  }
  
                  produced = emitted;
                  consumed = polled;
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
  
          }
  
          @Override
          void runBackfused() {
              int missed = 1;
  
              for (;;) {
  
                  if (cancelled) {
                      return;
                  }
  
                  boolean d = done;
  
                  downstream.onNext(null);
  
                  if (d) {
                      cancelled = true;
                      Throwable e = error;
                      if (e != null) {
                          downstream.onError(e);
                      } else {
                          downstream.onComplete();
                      }
                      worker.dispose();
                      return;
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          @Nullable
          @Override
          public T poll() throws Throwable {
              T v = queue.poll();
              if (v != null && sourceMode != SYNC) {
                  long p = consumed + 1;
                  if (p == limit) {
                      consumed = 0;
                      upstream.request(p);
                  } else {
                      consumed = p;
                  }
              }
              return v;
          }
      }
  }
  