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// Original file Copyright Crytek GMBH or its affiliates, used under license.
// This is free and unencumbered software released into the public domain.

// Anyone is free to copy, modify, publish, use, compile, sell, or
// distribute this software, either in source code form or as a compiled
// binary, for any purpose, commercial or non-commercial, and by any
// means.

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// software to the public domain. We make this dedication for the benefit
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// software under copyright law.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// For more information, please refer to <http://unlicense.org/>


// non-intrusive lock free unbounded SPSC queue
// the algorithm was taken from the blog post below, and converted to C++11
// http://cbloomrants.blogspot.com/2009/02/02-26-09-low-level-threading-part-51.html

#ifndef __SPSC_QUEUE_INCLUDED__
#define __SPSC_QUEUE_INCLUDED__

#include <atomic>

namespace concqueue
{
    template<typename T>
    class spsc_queue_t
    {
    public:

        spsc_queue_t()
            : _head(reinterpret_cast<node_t*>(new node_aligned_t))
            , _tail(_head)
        {
            _head->next = NULL;
        }

        ~spsc_queue_t()
        {
            T output;
            while (this->dequeue(output))
            {
            }
            delete _head;
        }

        bool enqueue(const T& input)
        {
            node_t* node = reinterpret_cast<node_t*>(new node_aligned_t);
            node->data = input;
            node->next = NULL;

            std::atomic_thread_fence(std::memory_order_acq_rel);
            _head->next = node;
            _head = node;
            return true;
        }

        bool dequeue(T& output)
        {
            std::atomic_thread_fence(std::memory_order_consume);
            if (!_tail->next)
            {
                return false;
            }

            output = _tail->next->data;
            std::atomic_thread_fence(std::memory_order_acq_rel);
            _back = _tail;
            _tail = _back->next;

            delete _back;
            return true;
        }


    private:

        struct node_t
        {
            node_t* next;
            T       data;
        };

        typedef typename std::aligned_storage<sizeof(node_t), std::alignment_of<node_t>::value>::type node_aligned_t;

        node_t* _head;
        char    _cache_line[64];
        node_t* _tail;
        node_t* _back;

        spsc_queue_t(const spsc_queue_t&) {}
        void operator=(const spsc_queue_t&) {}
    };
}

#endif