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.util;
  
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.reactivestreams.Subscriber;
  
  import io.reactivex.rxjava3.core.Observer;
  
  /**
   * Utility methods to perform half-serialization: a form of serialization
   * where onNext is guaranteed to be called from a single thread but
   * onError or onComplete may be called from any threads.
   */
  public final class HalfSerializer {
      /** Utility class. */
      private HalfSerializer() {
          throw new IllegalStateException("No instances!");
      }
  
      /**
       * Emits the given value if possible and terminates if there was an onComplete or onError
       * while emitting, drops the value otherwise.
       * @param <T> the value type
       * @param subscriber the target Subscriber to emit to
       * @param value the value to emit
       * @param wip the serialization work-in-progress counter/indicator
       * @param errors the holder of Throwables
       * @return true if the operation succeeded, false if there sequence completed
       */
      public static <T> boolean onNext(Subscriber<? super T> subscriber, T value,
              AtomicInteger wip, AtomicThrowable errors) {
          if (wip.get() == 0 && wip.compareAndSet(0, 1)) {
              subscriber.onNext(value);
              if (wip.decrementAndGet() == 0) {
                  return true;
              }
              errors.tryTerminateConsumer(subscriber);
          }
          return false;
      }
  
      /**
       * Emits the given exception if possible or adds it to the given error container to
       * be emitted by a concurrent onNext if one is running.
       * Undeliverable exceptions are sent to the RxJavaPlugins.onError.
       * @param subscriber the target Subscriber to emit to
       * @param ex the Throwable to emit
       * @param wip the serialization work-in-progress counter/indicator
       * @param errors the holder of Throwables
       */
      public static void onError(Subscriber<?> subscriber, Throwable ex,
              AtomicInteger wip, AtomicThrowable errors) {
          if (errors.tryAddThrowableOrReport(ex)) {
              if (wip.getAndIncrement() == 0) {
                  errors.tryTerminateConsumer(subscriber);
              }
          }
      }
  
      /**
       * Emits an onComplete signal or an onError signal with the given error or indicates
       * the concurrently running onNext should do that.
       * @param subscriber the target Subscriber to emit to
       * @param wip the serialization work-in-progress counter/indicator
       * @param errors the holder of Throwables
       */
      public static void onComplete(Subscriber<?> subscriber, AtomicInteger wip, AtomicThrowable errors) {
          if (wip.getAndIncrement() == 0) {
              errors.tryTerminateConsumer(subscriber);
          }
      }
  
      /**
       * Emits the given value if possible and terminates if there was an onComplete or onError
       * while emitting, drops the value otherwise.
       * @param <T> the value type
       * @param observer the target Observer to emit to
       * @param value the value to emit
       * @param wip the serialization work-in-progress counter/indicator
       * @param errors the holder of Throwables
       */
      public static <T> void onNext(Observer<? super T> observer, T value,
              AtomicInteger wip, AtomicThrowable errors) {
          if (wip.get() == 0 && wip.compareAndSet(0, 1)) {
              observer.onNext(value);
              if (wip.decrementAndGet() != 0) {
                  errors.tryTerminateConsumer(observer);
              }
          }
      }
  
      /**
       * Emits the given exception if possible or adds it to the given error container to
       * be emitted by a concurrent onNext if one is running.
       * Undeliverable exceptions are sent to the RxJavaPlugins.onError.
       * @param observer the target Subscriber to emit to
       * @param ex the Throwable to emit
       * @param wip the serialization work-in-progress counter/indicator
       * @param errors the holder of Throwables
       */
      public static void onError(Observer<?> observer, Throwable ex,
              AtomicInteger wip, AtomicThrowable errors) {
          if (errors.tryAddThrowableOrReport(ex)) {
              if (wip.getAndIncrement() == 0) {
                  errors.tryTerminateConsumer(observer);
              }
          }
      }
  
      /**
       * Emits an onComplete signal or an onError signal with the given error or indicates
       * the concurrently running onNext should do that.
       * @param observer the target Subscriber to emit to
       * @param wip the serialization work-in-progress counter/indicator
       * @param errors the holder of Throwables
       */
      public static void onComplete(Observer<?> observer, AtomicInteger wip, AtomicThrowable errors) {
          if (wip.getAndIncrement() == 0) {
              errors.tryTerminateConsumer(observer);
          }
      }
  
  }
  