SafeQueue.hpp

/*
 * SafeQueue.hpp
 * Copyright (C) 2019 Alfredo Pons Menargues <apons@linucleus.com>
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef SAFEQUEUE_HPP_
#define SAFEQUEUE_HPP_

#include <queue>
#include <list>
#include <mutex>
#include <thread>
#include <cstdint>
#include <condition_variable>
 
 
 
/** A thread-safe asynchronous queue */
template <class T, class Container = std::list<T>>
class SafeQueue
{
 
    typedef typename Container::value_type value_type;
    typedef typename Container::size_type size_type;
    typedef Container container_type;
 
  public:
 
    /*! Create safe queue. */
    SafeQueue() = default;
    SafeQueue (SafeQueue&& sq)
    {
      m_queue = std::move (sq.m_queue);
    }
    SafeQueue (const SafeQueue& sq)
    {
      std::lock_guard<std::mutex> lock (sq.m_mutex);
      m_queue = sq.m_queue;
    }
 
    /*! Destroy safe queue. */
    ~SafeQueue()
    {
      std::lock_guard<std::mutex> lock (m_mutex);
    }
 
    /**
     * Sets the maximum number of items in the queue. Defaults is 0: No limit
     * \param[in] item An item.
     */
    void set_max_num_items (unsigned int max_num_items)
    {
      m_max_num_items = max_num_items;
    }
 
    /**
     *  Pushes the item into the queue.
     * \param[in] item An item.
     * \return true if an item was pushed into the queue
     */
    bool push (const value_type& item)
    {
      std::lock_guard<std::mutex> lock (m_mutex);
 
      if (m_max_num_items > 0 && m_queue.size() > m_max_num_items)
        return false;
 
      m_queue.push (item);
      m_condition.notify_one();
      return true;
    }
 
    /**
     *  Pushes the item into the queue.
     * \param[in] item An item.
     * \return true if an item was pushed into the queue
     */
    bool push (const value_type&& item)
    {
      std::lock_guard<std::mutex> lock (m_mutex);
 
      if (m_max_num_items > 0 && m_queue.size() > m_max_num_items)
        return false;
 
      m_queue.push (item);
      m_condition.notify_one();
      return true;
    }
 
    /**
     *  Pops item from the queue. If queue is empty, this function blocks until item becomes available.
     * \param[out] item The item.
     */
    void pop (value_type& item)
    {
      std::unique_lock<std::mutex> lock (m_mutex);
      m_condition.wait (lock, [this]() // Lambda funct
      {
        return !m_queue.empty();
      });
      item = m_queue.front();
      m_queue.pop();
    }
 
    /**
     *  Pops item from the queue using the contained type's move assignment operator, if it has one..
     *  This method is identical to the pop() method if that type has no move assignment operator.
     *  If queue is empty, this function blocks until item becomes available.
     * \param[out] item The item.
     */
    void move_pop (value_type& item)
    {
      std::unique_lock<std::mutex> lock (m_mutex);
      m_condition.wait (lock, [this]() // Lambda funct
      {
        return !m_queue.empty();
      });
      item = std::move (m_queue.front());
      m_queue.pop();
    }
 
    /**
     *  Tries to pop item from the queue.
     * \param[out] item The item.
     * \return False is returned if no item is available.
     */
    bool try_pop (value_type& item)
    {
      std::unique_lock<std::mutex> lock (m_mutex);
 
      if (m_queue.empty())
        return false;
 
      item = m_queue.front();
      m_queue.pop();
      return true;
    }
 
    /**
     *  Tries to pop item from the queue using the contained type's move assignment operator, if it has one..
     *  This method is identical to the try_pop() method if that type has no move assignment operator.
     * \param[out] item The item.
     * \return False is returned if no item is available.
     */
    bool try_move_pop (value_type& item)
    {
      std::unique_lock<std::mutex> lock (m_mutex);
 
      if (m_queue.empty())
        return false;
 
      item = std::move (m_queue.front());
      m_queue.pop();
      return true;
    }
 
    /**
     *  Pops item from the queue. If the queue is empty, blocks for timeout microseconds, or until item becomes available.
     * \param[out] t An item.
     * \param[in] timeout The number of microseconds to wait.
     * \return true if get an item from the queue, false if no item is received before the timeout.
     */
    bool timeout_pop (value_type& item, std::uint64_t timeout)
    {
      std::unique_lock<std::mutex> lock (m_mutex);
 
      if (m_queue.empty())
        {
          if (timeout == 0)
            return false;
 
          if (m_condition.wait_for (lock, std::chrono::microseconds (timeout)) == std::cv_status::timeout)
            return false;
        }
 
      item = m_queue.front();
      m_queue.pop();
      return true;
    }
 
    /**
     *  Pops item from the queue using the contained type's move assignment operator, if it has one..
     *  If the queue is empty, blocks for timeout microseconds, or until item becomes available.
     *  This method is identical to the try_pop() method if that type has no move assignment operator.
     * \param[out] t An item.
     * \param[in] timeout The number of microseconds to wait.
     * \return true if get an item from the queue, false if no item is received before the timeout.
     */
    bool timeout_move_pop (value_type& item, std::uint64_t timeout)
    {
      std::unique_lock<std::mutex> lock (m_mutex);
 
      if (m_queue.empty())
        {
          if (timeout == 0)
            return false;
 
          if (m_condition.wait_for (lock, std::chrono::microseconds (timeout)) == std::cv_status::timeout)
            return false;
        }
 
      item = std::move (m_queue.front());
      m_queue.pop();
      return true;
    }
 
    /**
     *  Gets the number of items in the queue.
     * \return Number of items in the queue.
     */
    size_type size() const
    {
      std::lock_guard<std::mutex> lock (m_mutex);
      return m_queue.size();
    }
 
    /**
     *  Check if the queue is empty.
     * \return true if queue is empty.
     */
    bool empty() const
    {
      std::lock_guard<std::mutex> lock (m_mutex);
      return m_queue.empty();
    }
 
    /**
     *  Swaps the contents.
     * \param[out] sq The SafeQueue to swap with 'this'.
     */
    void swap (SafeQueue& sq)
    {
      if (this != &sq)
        {
          std::lock_guard<std::mutex> lock1 (m_mutex);
          std::lock_guard<std::mutex> lock2 (sq.m_mutex);
          m_queue.swap (sq.m_queue);
 
          if (!m_queue.empty())
            m_condition.notify_all();
 
          if (!sq.m_queue.empty())
            sq.m_condition.notify_all();
        }
    }
 
    /*! The copy assignment operator */
    SafeQueue& operator= (const SafeQueue& sq)
    {
      if (this != &sq)
        {
          std::lock_guard<std::mutex> lock1 (m_mutex);
          std::lock_guard<std::mutex> lock2 (sq.m_mutex);
          std::queue<T, Container> temp {sq.m_queue};
          m_queue.swap (temp);
 
          if (!m_queue.empty())
            m_condition.notify_all();
        }
 
      return *this;
    }
 
    /*! The move assignment operator */
    SafeQueue& operator= (SafeQueue && sq)
    {
      std::lock_guard<std::mutex> lock (m_mutex);
      m_queue = std::move (sq.m_queue);
 
      if (!m_queue.empty())  m_condition.notify_all();
 
      return *this;
    }
 
 
  private:
 
    std::queue<T, Container> m_queue;
    mutable std::mutex m_mutex;
    std::condition_variable m_condition;
    unsigned int m_max_num_items = 0;
};
 
/*! Swaps the contents of two SafeQueue objects. */
template <class T, class Container>
void swap (SafeQueue<T, Container>& q1, SafeQueue<T, Container>& q2)
{
  q1.swap (q2);
}
#endif /* SAFEQUEUE_HPP_ */