text: /*
   * Copyright (c) Facebook, Inc. and its affiliates.
   *
   * 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.
   */
  
  #pragma once
  
  #include <chrono>
  #include <exception>
  #include <stdexcept>
  
  #include <glog/logging.h>
  
  #include <folly/CPortability.h>
  #include <folly/Optional.h>
  
  namespace folly {
  
  // Some queue implementations (for example, LifoSemMPMCQueue or
  // PriorityLifoSemMPMCQueue) support both blocking (BLOCK) and
  // non-blocking (THROW) behaviors.
  enum class QueueBehaviorIfFull { THROW, BLOCK };
  
  class FOLLY_EXPORT QueueFullException : public std::runtime_error {
    using std::runtime_error::runtime_error; // Inherit constructors.
  };
  
  struct BlockingQueueAddResult {
    BlockingQueueAddResult(bool reused = false) : reusedThread(reused) {}
    bool reusedThread;
  };
  
  template <class T>
  class BlockingQueue {
   public:
    virtual ~BlockingQueue() = default;
    // Adds item to the queue (with priority).
    //
    // Returns true if an existing thread was able to work on it (used
    // for dynamically sizing thread pools), false otherwise.  Return false
    // if this feature is not supported.
    virtual BlockingQueueAddResult add(T item) = 0;
    virtual BlockingQueueAddResult addWithPriority(
        T item,
        int8_t /* priority */) {
      return add(std::move(item));
    }
    virtual uint8_t getNumPriorities() { return 1; }
    virtual T take() = 0;
    virtual folly::Optional<T> try_take_for(std::chrono::milliseconds time) = 0;
    virtual size_t size() = 0;
  };
  
  } // namespace folly
  