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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/>

// C++ implementation of Dmitry Vyukov's non-intrusive lock free unbound MPSC queue
// http://www.1024cores.net/home/lock-free-algorithms/queues/non-intrusive-mpsc-node-based-queue

#ifndef __MPSC_BOUNDED_QUEUE_INCLUDED__
#define __MPSC_BOUNDED_QUEUE_INCLUDED__

#include <atomic>
#include <assert.h>

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

        mpsc_queue_t()
            : _head(reinterpret_cast<buffer_node_t*>(new buffer_node_aligned_t))
            , _tail(_head.load(std::memory_order_relaxed))
        {
            buffer_node_t* front = _head.load(std::memory_order_relaxed);
            front->next.store(NULL, std::memory_order_relaxed);
        }

        ~mpsc_queue_t()
        {
            T output;
            while (this->dequeue(output))
            {
            }
            buffer_node_t* front = _head.load(std::memory_order_relaxed);
            delete front;
        }

        bool enqueue(const T& input)
        {
            buffer_node_t* node = reinterpret_cast<buffer_node_t*>(new buffer_node_aligned_t);
            node->data = input;
            node->next.store(NULL, std::memory_order_relaxed);

            buffer_node_t* prev_head = _head.exchange(node, std::memory_order_acq_rel);
            prev_head->next.store(node, std::memory_order_release);
            return true;
        }

        bool dequeue(T& output)
        {
            buffer_node_t* tail = _tail.load(std::memory_order_relaxed);
            buffer_node_t* next = tail->next.load(std::memory_order_acquire);

            if (next == NULL)
            {
                return false;
            }

            output = next->data;
            _tail.store(next, std::memory_order_release);
            delete tail;
            return true;
        }


    private:

        struct buffer_node_t
        {
            T                           data;
            std::atomic<buffer_node_t*> next;
        };

        typedef typename std::aligned_storage<sizeof(buffer_node_t), std::alignment_of<buffer_node_t>::value>::type buffer_node_aligned_t;

        std::atomic<buffer_node_t*> _head;
        std::atomic<buffer_node_t*> _tail;

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

#endif