ThreadSafeQueue.hpp

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/***************************************************
 *       _   _            _                        *
 *      | | | |          (_)                       *
 *      | |_| | ___  _ __ _ _______  _ __          *
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 ***************************************************
 * This file is part of Horizon (c).
 *
 * Copyright (c) 2019 Sagun K. (sagunxp@gmail.com).
 * Copyright (c) 2019 Horizon Dev Team.
 *
 * This library 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 library 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 library.  If not, see <http://www.gnu.org/licenses/>.
 **************************************************/
 
#ifndef HORIZON_CORE_MULTITHREADING_THREADSAFEQUEUE_HPP
#define HORIZON_CORE_MULTITHREADING_THREADSAFEQUEUE_HPP
 
#include <memory>
#include <thread>
#include <mutex>
 
template<typename T>
class ThreadSafeQueue
{
private:
    struct node
    {
        std::shared_ptr<T> data;
        std::unique_ptr<node> next;
    };
 
    std::mutex head_mutex;
    std::unique_ptr<node> head;
    std::mutex tail_mutex;
    node *tail;
 
    node *get_tail()
    {
        std::unique_lock<std::mutex> tail_lock(tail_mutex);
        return tail;
    }
 
    std::unique_ptr<node> pop_head()
    {
        std::unique_lock<std::mutex> head_lock(head_mutex);
 
        if(head.get() == get_tail())
            return nullptr;
 
        std::unique_ptr<node> old_head = std::move(head);
        head = std::move(old_head->next);
        return old_head;
    }
 
public:
    ThreadSafeQueue():
        head(new node), tail(head.get())
    {}
 
    ~ThreadSafeQueue()
    {
        std::size_t qsize = size();
 
        for (std::size_t i = 0; i < qsize; i++)
            try_pop();
    }
 
    ThreadSafeQueue(const ThreadSafeQueue &other)=delete;
    ThreadSafeQueue &operator=(const ThreadSafeQueue &other)=delete;
 
    std::shared_ptr<T> try_pop()
    {
        std::unique_ptr<node> old_head = pop_head();
        return old_head ? old_head->data : std::shared_ptr<T>();
    }
 
    void push(T &&new_value)
    {
        std::shared_ptr<T> new_data(
            std::make_shared<T>(std::move(new_value)));
        std::unique_ptr<node> p(new node);
        node *new_tail = p.get();
        std::unique_lock<std::mutex> tail_lock(tail_mutex);
        tail->data = new_data;
        tail->next = std::move(p);
        tail = new_tail;
    }
 
    std::size_t size()
    {
        int count = 0;
        std::unique_lock<std::mutex> head_lock(head_mutex);
        std::unique_lock<std::mutex> tail_lock(tail_mutex);
        node const *n = head.get();
 
        while ((n = n->next.get())) {
            count++;
        }
 
        return count;
    }
 
    bool empty()
    {
        std::unique_lock<std::mutex> head_lock(head_mutex);
 
        if(head.get() == get_tail())
            return true;
 
        return false;
    }
 
    std::shared_ptr<T> front()
    {
        std::unique_lock<std::mutex> head_lock(head_mutex);
        std::shared_ptr<T> front = head != nullptr ? std::make_shared<T>(*head->data) : nullptr;
        return std::move(front);
    }
};
 
#endif // HORIZON_CORE_MULTITHREADING_THREADSAFEQUEUE_HPP