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 io.reactivex.rxjava3.core.Observer;
  
  public interface ObservableQueueDrain<T, U> {
  
      boolean cancelled();
  
      boolean done();
  
      Throwable error();
  
      boolean enter();
  
      /**
       * Adds m to the wip counter.
       * @param m the value to add
       * @return the wip value after adding the value
       */
      int leave(int m);
  
      /**
       * Accept the value and return true if forwarded.
       * @param a the subscriber to deliver values to
       * @param v the value to deliver
       */
      void accept(Observer<? super U> a, T v);
  }
  