//  lock-free queue from
	//  Michael, M. M. and Scott, M. L.,
	//  "simple, fast and practical non-blocking and blocking concurrent queue algorithms"
	//
	//  Copyright (C) 2008-2013 Tim Blechmann
	//
	//  Distributed under the Boost Software License, Version 1.0. (See
	//  accompanying file LICENSE_1_0.txt or copy at
	//  http://www.boost.org/LICENSE_1_0.txt)
	
	#ifndef BOOST_LOCKFREE_FIFO_HPP_INCLUDED
	#define BOOST_LOCKFREE_FIFO_HPP_INCLUDED
	
	#include <boost/assert.hpp>
	#include <boost/static_assert.hpp>
	#include <boost/type_traits/has_trivial_assign.hpp>
	#include <boost/type_traits/has_trivial_destructor.hpp>
	#include <boost/config.hpp> // for BOOST_LIKELY & BOOST_ALIGNMENT
	
	#include <boost/lockfree/detail/atomic.hpp>
	#include <boost/lockfree/detail/copy_payload.hpp>
	#include <boost/lockfree/detail/freelist.hpp>
	#include <boost/lockfree/detail/parameter.hpp>
	#include <boost/lockfree/detail/tagged_ptr.hpp>
	
	#include <boost/lockfree/lockfree_forward.hpp>
	
	#ifdef BOOST_HAS_PRAGMA_ONCE
	#pragma once
	#endif
	
	
	#if defined(_MSC_VER)
	#pragma warning(push)
	#pragma warning(disable: 4324) // structure was padded due to __declspec(align())
	#endif
	
	
	namespace boost    {
	namespace lockfree {
	namespace detail   {
	
	typedef parameter::parameters<boost::parameter::optional<tag::allocator>,
	                              boost::parameter::optional<tag::capacity>
	                             > queue_signature;
	
	} /* namespace detail */
	
	
	/** The queue class provides a multi-writer/multi-reader queue, pushing and popping is lock-free,
	 *  construction/destruction has to be synchronized. It uses a freelist for memory management,
	 *  freed nodes are pushed to the freelist and not returned to the OS before the queue is destroyed.
	 *
	 *  \b Policies:
	 *  - \ref boost::lockfree::fixed_sized, defaults to \c boost::lockfree::fixed_sized<false> \n
	 *    Can be used to completely disable dynamic memory allocations during push in order to ensure lockfree behavior. \n
	 *    If the data structure is configured as fixed-sized, the internal nodes are stored inside an array and they are addressed
	 *    by array indexing. This limits the possible size of the queue to the number of elements that can be addressed by the index
	 *    type (usually 2**16-2), but on platforms that lack double-width compare-and-exchange instructions, this is the best way
	 *    to achieve lock-freedom.
	 *
	 *  - \ref boost::lockfree::capacity, optional \n
	 *    If this template argument is passed to the options, the size of the queue is set at compile-time.\n
	 *    This option implies \c fixed_sized<true>
	 *
	 *  - \ref boost::lockfree::allocator, defaults to \c boost::lockfree::allocator<std::allocator<void>> \n
	 *    Specifies the allocator that is used for the internal freelist
	 *
	 *  \b Requirements:
	 *   - T must have a copy constructor
	 *   - T must have a trivial assignment operator
	 *   - T must have a trivial destructor
	 *
	 * */
	#ifdef BOOST_NO_CXX11_VARIADIC_TEMPLATES
	template <typename T, class A0, class A1, class A2>
	#else
	template <typename T, typename ...Options>
	#endif
	class queue
	{
	private:
	#ifndef BOOST_DOXYGEN_INVOKED
	
	#ifdef BOOST_HAS_TRIVIAL_DESTRUCTOR
	    BOOST_STATIC_ASSERT((boost::has_trivial_destructor<T>::value));
	#endif
	
	#ifdef BOOST_HAS_TRIVIAL_ASSIGN
	    BOOST_STATIC_ASSERT((boost::has_trivial_assign<T>::value));
	#endif
	
	#ifdef BOOST_NO_CXX11_VARIADIC_TEMPLATES
	    typedef typename detail::queue_signature::bind<A0, A1, A2>::type bound_args;
	#else
	    typedef typename detail::queue_signature::bind<Options...>::type bound_args;
	#endif
	
	    static const bool has_capacity = detail::extract_capacity<bound_args>::has_capacity;
	    static const size_t capacity = detail::extract_capacity<bound_args>::capacity + 1; // the queue uses one dummy node
	    static const bool fixed_sized = detail::extract_fixed_sized<bound_args>::value;
	    static const bool node_based = !(has_capacity || fixed_sized);
	    static const bool compile_time_sized = has_capacity;
	
	    struct BOOST_ALIGNMENT(BOOST_LOCKFREE_CACHELINE_BYTES) node
	    {
	        typedef typename detail::select_tagged_handle<node, node_based>::tagged_handle_type tagged_node_handle;
	        typedef typename detail::select_tagged_handle<node, node_based>::handle_type handle_type;
	
	        node(T const & v, handle_type null_handle):
	            next(tagged_node_handle(null_handle, 0)), data(v)
	        {
	            /* increment tag to avoid ABA problem */
	            tagged_node_handle old_next = next.load(memory_order_relaxed);
	            tagged_node_handle new_next (null_handle, old_next.get_next_tag());
	            next.store(new_next, memory_order_release);
	        }
	
	        node (handle_type null_handle):
	            next(tagged_node_handle(null_handle, 0))

	        {}
	
	        node(void)
	        {}
	
	        atomic<tagged_node_handle> next;
	        T data;
	    };
	
	    typedef typename detail::extract_allocator<bound_args, node>::type node_allocator;
	    typedef typename detail::select_freelist<node, node_allocator, compile_time_sized, fixed_sized, capacity>::type pool_t;
	    typedef typename pool_t::tagged_node_handle tagged_node_handle;
	    typedef typename detail::select_tagged_handle<node, node_based>::handle_type handle_type;
	
	    void initialize(void)
	    {
	        node * n = pool.template construct<true, false>(pool.null_handle());
	        tagged_node_handle dummy_node(pool.get_handle(n), 0);
	        head_.store(dummy_node, memory_order_relaxed);
	        tail_.store(dummy_node, memory_order_release);
	    }
	
	    struct implementation_defined
	    {
	        typedef node_allocator allocator;
	        typedef std::size_t size_type;
	    };
	
	#endif
	
	    BOOST_DELETED_FUNCTION(queue(queue const&))
	    BOOST_DELETED_FUNCTION(queue& operator= (queue const&))
	
	public:
	    typedef T value_type;
	    typedef typename implementation_defined::allocator allocator;
	    typedef typename implementation_defined::size_type size_type;
	
	    /**
	     * \return true, if implementation is lock-free.
	     *
	     * \warning It only checks, if the queue head and tail nodes and the freelist can be modified in a lock-free manner.
	     *       On most platforms, the whole implementation is lock-free, if this is true. Using c++0x-style atomics, there is
	     *       no possibility to provide a completely accurate implementation, because one would need to test every internal
	     *       node, which is impossible if further nodes will be allocated from the operating system.
	     * */
	    bool is_lock_free (void) const
	    {
	        return head_.is_lock_free() && tail_.is_lock_free() && pool.is_lock_free();
	    }
	
	    //! Construct queue
	    // @{
	    queue(void):
	        head_(tagged_node_handle(0, 0)),
	        tail_(tagged_node_handle(0, 0)),
	        pool(node_allocator(), capacity)
	    {
	        BOOST_ASSERT(has_capacity);
	        initialize();
	    }
	
	    template <typename U>
	    explicit queue(typename node_allocator::template rebind<U>::other const & alloc):
	        head_(tagged_node_handle(0, 0)),
	        tail_(tagged_node_handle(0, 0)),
	        pool(alloc, capacity)
	    {
	        BOOST_STATIC_ASSERT(has_capacity);
	        initialize();
	    }
	
	    explicit queue(allocator const & alloc):
	        head_(tagged_node_handle(0, 0)),
	        tail_(tagged_node_handle(0, 0)),
	        pool(alloc, capacity)
	    {
	        BOOST_ASSERT(has_capacity);
	        initialize();
	    }
	    // @}
	
	    //! Construct queue, allocate n nodes for the freelist.
	    // @{
	    explicit queue(size_type n):
	        head_(tagged_node_handle(0, 0)),
	        tail_(tagged_node_handle(0, 0)),
	        pool(node_allocator(), n + 1)
	    {
	        BOOST_ASSERT(!has_capacity);
	        initialize();
	    }
	
	    template <typename U>
	    queue(size_type n, typename node_allocator::template rebind<U>::other const & alloc):
	        head_(tagged_node_handle(0, 0)),
	        tail_(tagged_node_handle(0, 0)),
	        pool(alloc, n + 1)
	    {
	        BOOST_STATIC_ASSERT(!has_capacity);
	        initialize();
	    }
	    // @}
	
	    /** \copydoc boost::lockfree::stack::reserve
	     * */
	    void reserve(size_type n)
	    {
	        pool.template reserve<true>(n);
	    }
	
	    /** \copydoc boost::lockfree::stack::reserve_unsafe
	     * */
	    void reserve_unsafe(size_type n)
	    {
	        pool.template reserve<false>(n);
	    }
	
	    /** Destroys queue, free all nodes from freelist.
	     * */
	    ~queue(void)
	    {
	        T dummy;
	        while(unsynchronized_pop(dummy))
	        {}
	
	        pool.template destruct<false>(head_.load(memory_order_relaxed));
	    }
	
	    /** Check if the queue is empty
	     *
	     * \return true, if the queue is empty, false otherwise
	     * \note The result is only accurate, if no other thread modifies the queue. Therefore it is rarely practical to use this
	     *       value in program logic.
	     * */
	    bool empty(void) const
	    {
	        return pool.get_handle(head_.load()) == pool.get_handle(tail_.load());
	    }
	
	    /** Pushes object t to the queue.
	     *
	     * \post object will be pushed to the queue, if internal node can be allocated
	     * \returns true, if the push operation is successful.
	     *
	     * \note Thread-safe. If internal memory pool is exhausted and the memory pool is not fixed-sized, a new node will be allocated
	     *                    from the OS. This may not be lock-free.
	     * */
	    bool push(T const & t)
	    {
	        return do_push<false>(t);
	    }
	
	    /** Pushes object t to the queue.
	     *
	     * \post object will be pushed to the queue, if internal node can be allocated
	     * \returns true, if the push operation is successful.
	     *
	     * \note Thread-safe and non-blocking. If internal memory pool is exhausted, operation will fail
	     * \throws if memory allocator throws
	     * */
	    bool bounded_push(T const & t)
	    {
	        return do_push<true>(t);
	    }
	
	
	private:
	#ifndef BOOST_DOXYGEN_INVOKED
	    template <bool Bounded>
	    bool do_push(T const & t)
	    {
	        node * n = pool.template construct<true, Bounded>(t, pool.null_handle());
	        handle_type node_handle = pool.get_handle(n);
	
	        if (n == NULL)
	            return false;
	
	        for (;;) {
	            tagged_node_handle tail = tail_.load(memory_order_acquire);
	            node * tail_node = pool.get_pointer(tail);
	            tagged_node_handle next = tail_node->next.load(memory_order_acquire);
	            node * next_ptr = pool.get_pointer(next);
	
	            tagged_node_handle tail2 = tail_.load(memory_order_acquire);
	            if (BOOST_LIKELY(tail == tail2)) {
	                if (next_ptr == 0) {
	                    tagged_node_handle new_tail_next(node_handle, next.get_next_tag());
	                    if ( tail_node->next.compare_exchange_weak(next, new_tail_next) ) {
	                        tagged_node_handle new_tail(node_handle, tail.get_next_tag());
	                        tail_.compare_exchange_strong(tail, new_tail);
	                        return true;
	                    }
	                }
	                else {
	                    tagged_node_handle new_tail(pool.get_handle(next_ptr), tail.get_next_tag());
	                    tail_.compare_exchange_strong(tail, new_tail);
	                }
	            }
	        }
	    }
	#endif
	
	public:
	
	    /** Pushes object t to the queue.
	     *
	     * \post object will be pushed to the queue, if internal node can be allocated
	     * \returns true, if the push operation is successful.
	     *
	     * \note Not Thread-safe. If internal memory pool is exhausted and the memory pool is not fixed-sized, a new node will be allocated
	     *       from the OS. This may not be lock-free.
	     * \throws if memory allocator throws
	     * */
	    bool unsynchronized_push(T const & t)
	    {
	        node * n = pool.template construct<false, false>(t, pool.null_handle());
	
	        if (n == NULL)
	            return false;
	
	        for (;;) {
	            tagged_node_handle tail = tail_.load(memory_order_relaxed);
	            tagged_node_handle next = tail->next.load(memory_order_relaxed);
	            node * next_ptr = next.get_ptr();
	
	            if (next_ptr == 0) {
	                tail->next.store(tagged_node_handle(n, next.get_next_tag()), memory_order_relaxed);
	                tail_.store(tagged_node_handle(n, tail.get_next_tag()), memory_order_relaxed);
	                return true;
	            }
	            else
	                tail_.store(tagged_node_handle(next_ptr, tail.get_next_tag()), memory_order_relaxed);
	        }
	    }
	
	    /** Pops object from queue.
	     *
	     * \post if pop operation is successful, object will be copied to ret.
	     * \returns true, if the pop operation is successful, false if queue was empty.
	     *
	     * \note Thread-safe and non-blocking
	     * */
	    bool pop (T & ret)
	    {
	        return pop<T>(ret);
	    }
	
	    /** Pops object from queue.
	     *
	     * \pre type U must be constructible by T and copyable, or T must be convertible to U
	     * \post if pop operation is successful, object will be copied to ret.
	     * \returns true, if the pop operation is successful, false if queue was empty.
	     *
	     * \note Thread-safe and non-blocking
	     * */
	    template <typename U>
	    bool pop (U & ret)
	    {
	        for (;;) {
	            tagged_node_handle head = head_.load(memory_order_acquire);
	            node * head_ptr = pool.get_pointer(head);
	
	            tagged_node_handle tail = tail_.load(memory_order_acquire);
	            tagged_node_handle next = head_ptr->next.load(memory_order_acquire);
	            node * next_ptr = pool.get_pointer(next);
	
	            tagged_node_handle head2 = head_.load(memory_order_acquire);
	            if (BOOST_LIKELY(head == head2)) {
	                if (pool.get_handle(head) == pool.get_handle(tail)) {
	                    if (next_ptr == 0)
	                        return false;
	
	                    tagged_node_handle new_tail(pool.get_handle(next), tail.get_next_tag());
	                    tail_.compare_exchange_strong(tail, new_tail);
	
	                } else {
	                    if (next_ptr == 0)
	                        /* this check is not part of the original algorithm as published by michael and scott
	                         *
	                         * however we reuse the tagged_ptr part for the freelist and clear the next part during node
	                         * allocation. we can observe a null-pointer here.
	                         * */
	                        continue;
	                    detail::copy_payload(next_ptr->data, ret);
	
	                    tagged_node_handle new_head(pool.get_handle(next), head.get_next_tag());
	                    if (head_.compare_exchange_weak(head, new_head)) {
	                        pool.template destruct<true>(head);
	                        return true;
	                    }
	                }
	            }
	        }
	    }
	
	    /** Pops object from queue.
	     *
	     * \post if pop operation is successful, object will be copied to ret.
	     * \returns true, if the pop operation is successful, false if queue was empty.
	     *
	     * \note Not thread-safe, but non-blocking
	     *
	     * */
	    bool unsynchronized_pop (T & ret)
	    {
	        return unsynchronized_pop<T>(ret);
	    }
	
	    /** Pops object from queue.
	     *
	     * \pre type U must be constructible by T and copyable, or T must be convertible to U
	     * \post if pop operation is successful, object will be copied to ret.
	     * \returns true, if the pop operation is successful, false if queue was empty.
	     *
	     * \note Not thread-safe, but non-blocking
	     *
	     * */
	    template <typename U>
	    bool unsynchronized_pop (U & ret)
	    {
	        for (;;) {
	            tagged_node_handle head = head_.load(memory_order_relaxed);
	            node * head_ptr = pool.get_pointer(head);
	            tagged_node_handle tail = tail_.load(memory_order_relaxed);
	            tagged_node_handle next = head_ptr->next.load(memory_order_relaxed);
	            node * next_ptr = pool.get_pointer(next);
	
	            if (pool.get_handle(head) == pool.get_handle(tail)) {
	                if (next_ptr == 0)
	                    return false;
	
	                tagged_node_handle new_tail(pool.get_handle(next), tail.get_next_tag());
	                tail_.store(new_tail);
	            } else {
	                if (next_ptr == 0)
	                    /* this check is not part of the original algorithm as published by michael and scott
	                     *
	                     * however we reuse the tagged_ptr part for the freelist and clear the next part during node
	                     * allocation. we can observe a null-pointer here.
	                     * */
	                    continue;
	                detail::copy_payload(next_ptr->data, ret);
	                tagged_node_handle new_head(pool.get_handle(next), head.get_next_tag());
	                head_.store(new_head);
	                pool.template destruct<false>(head);
	                return true;
	            }
	        }
	    }
	
	    /** consumes one element via a functor
	     *
	     *  pops one element from the queue and applies the functor on this object
	     *
	     * \returns true, if one element was consumed
	     *
	     * \note Thread-safe and non-blocking, if functor is thread-safe and non-blocking
	     * */
	    template <typename Functor>
	    bool consume_one(Functor & f)
	    {
	        T element;
	        bool success = pop(element);
	        if (success)
	            f(element);
	
	        return success;
	    }
	
	    /// \copydoc boost::lockfree::queue::consume_one(Functor & rhs)
	    template <typename Functor>
	    bool consume_one(Functor const & f)
	    {
	        T element;
	        bool success = pop(element);
	        if (success)
	            f(element);
	
	        return success;
	    }
	
	    /** consumes all elements via a functor
	     *
	     * sequentially pops all elements from the queue and applies the functor on each object
	     *
	     * \returns number of elements that are consumed
	     *
	     * \note Thread-safe and non-blocking, if functor is thread-safe and non-blocking
	     * */
	    template <typename Functor>
	    size_t consume_all(Functor & f)
	    {
	        size_t element_count = 0;
	        while (consume_one(f))
	            element_count += 1;
	
	        return element_count;
	    }
	
	    /// \copydoc boost::lockfree::queue::consume_all(Functor & rhs)
	    template <typename Functor>
	    size_t consume_all(Functor const & f)
	    {
	        size_t element_count = 0;
	        while (consume_one(f))
	            element_count += 1;
	
	        return element_count;
	    }
	
	private:
	#ifndef BOOST_DOXYGEN_INVOKED
	    atomic<tagged_node_handle> head_;
	    static const int padding_size = BOOST_LOCKFREE_CACHELINE_BYTES - sizeof(tagged_node_handle);
	    char padding1[padding_size];
	    atomic<tagged_node_handle> tail_;
	    char padding2[padding_size];
	
	    pool_t pool;
	#endif
	};
	
	} /* namespace lockfree */
	} /* namespace boost */
	
	#if defined(_MSC_VER)
	#pragma warning(pop)
	#endif
	
	#endif /* BOOST_LOCKFREE_FIFO_HPP_INCLUDED */