queue.h

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/* Copyright 2013-present Barefoot Networks, Inc.
 *
 * 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.
 */
 
/*
 * Antonin Bas (antonin@barefootnetworks.com)
 *
 */
 
 
#ifndef BM_BM_SIM_QUEUE_H_
#define BM_BM_SIM_QUEUE_H_
 
#include <condition_variable>
#include <deque>
#include <mutex>
#include <utility>
 
namespace bm {
 
/* TODO(antonin): implement non blocking read behavior */
 
template <class T>
class Queue {
 public:
  enum WriteBehavior {
    WriteBlock,
    WriteReturn
  };
  enum ReadBehavior {
    ReadBlock,
    ReadReturn
  };
 
 public:
  Queue()
    : capacity(1024), wb(WriteBlock), rb(ReadBlock) { }
 
  Queue(size_t capacity,
        WriteBehavior wb = WriteBlock, ReadBehavior rb = ReadBlock)
    : capacity(capacity), wb(wb), rb(rb) {}
 
  void push_front(const T &item) {
    std::unique_lock<std::mutex> lock(q_mutex);
    while (!is_not_full()) {
      if (wb == WriteReturn) return;
      q_not_full.wait(lock);
    }
    queue.push_front(item);
    lock.unlock();
    q_not_empty.notify_one();
  }
 
  void push_front(T &&item) {
    std::unique_lock<std::mutex> lock(q_mutex);
    while (!is_not_full()) {
      if (wb == WriteReturn) return;
      q_not_full.wait(lock);
    }
    queue.push_front(std::move(item));
    lock.unlock();
    q_not_empty.notify_one();
  }
 
  void pop_back(T* pItem) {
    std::unique_lock<std::mutex> lock(q_mutex);
    while (!is_not_empty())
      q_not_empty.wait(lock);
    *pItem = std::move(queue.back());
    queue.pop_back();
    lock.unlock();
    q_not_full.notify_one();
  }
 
  size_t size() const {
    std::unique_lock<std::mutex> lock(q_mutex);
    return queue.size();
  }
 
  void set_capacity(const size_t c) {
    // change capacity but does not discard elements
    std::unique_lock<std::mutex> lock(q_mutex);
    capacity = c;
  }
 
  Queue(const Queue &) = delete;
  Queue &operator =(const Queue &) = delete;
 
  Queue(Queue &&) = delete;
  Queue &&operator =(Queue &&) = delete;
 
 private:
  bool is_not_empty() const { return queue.size() > 0; }
  bool is_not_full() const { return queue.size() < capacity; }
 
  size_t capacity;
  std::deque<T> queue;
  WriteBehavior wb;
  ReadBehavior rb;
 
  mutable std::mutex q_mutex;
  mutable std::condition_variable q_not_empty;
  mutable std::condition_variable q_not_full;
};
 
}  // namespace bm
 
#endif  // BM_BM_SIM_QUEUE_H_