Chris@16: //  lock-free queue from
Chris@16: //  Michael, M. M. and Scott, M. L.,
Chris@16: //  "simple, fast and practical non-blocking and blocking concurrent queue algorithms"
Chris@16: //
Chris@16: //  Copyright (C) 2008-2013 Tim Blechmann
Chris@16: //
Chris@16: //  Distributed under the Boost Software License, Version 1.0. (See
Chris@16: //  accompanying file LICENSE_1_0.txt or copy at
Chris@16: //  http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_LOCKFREE_FIFO_HPP_INCLUDED
Chris@16: #define BOOST_LOCKFREE_FIFO_HPP_INCLUDED
Chris@16: 
Chris@16: #include <boost/assert.hpp>
Chris@16: #include <boost/static_assert.hpp>
Chris@16: #include <boost/type_traits/has_trivial_assign.hpp>
Chris@16: #include <boost/type_traits/has_trivial_destructor.hpp>
Chris@16: 
Chris@16: #include <boost/lockfree/detail/atomic.hpp>
Chris@16: #include <boost/lockfree/detail/copy_payload.hpp>
Chris@16: #include <boost/lockfree/detail/freelist.hpp>
Chris@16: #include <boost/lockfree/detail/parameter.hpp>
Chris@16: #include <boost/lockfree/detail/tagged_ptr.hpp>
Chris@16: 
Chris@101: #ifdef BOOST_HAS_PRAGMA_ONCE
Chris@101: #pragma once
Chris@101: #endif
Chris@101: 
Chris@101: 
Chris@16: #if defined(_MSC_VER)
Chris@16: #pragma warning(push)
Chris@16: #pragma warning(disable: 4324) // structure was padded due to __declspec(align())
Chris@16: #endif
Chris@16: 
Chris@16: 
Chris@16: namespace boost    {
Chris@16: namespace lockfree {
Chris@16: namespace detail   {
Chris@16: 
Chris@16: typedef parameter::parameters<boost::parameter::optional<tag::allocator>,
Chris@16:                               boost::parameter::optional<tag::capacity>
Chris@16:                              > queue_signature;
Chris@16: 
Chris@16: } /* namespace detail */
Chris@16: 
Chris@16: 
Chris@16: /** The queue class provides a multi-writer/multi-reader queue, pushing and popping is lock-free,
Chris@16:  *  construction/destruction has to be synchronized. It uses a freelist for memory management,
Chris@16:  *  freed nodes are pushed to the freelist and not returned to the OS before the queue is destroyed.
Chris@16:  *
Chris@16:  *  \b Policies:
Chris@16:  *  - \ref boost::lockfree::fixed_sized, defaults to \c boost::lockfree::fixed_sized<false> \n
Chris@16:  *    Can be used to completely disable dynamic memory allocations during push in order to ensure lockfree behavior. \n
Chris@16:  *    If the data structure is configured as fixed-sized, the internal nodes are stored inside an array and they are addressed
Chris@16:  *    by array indexing. This limits the possible size of the queue to the number of elements that can be addressed by the index
Chris@16:  *    type (usually 2**16-2), but on platforms that lack double-width compare-and-exchange instructions, this is the best way
Chris@16:  *    to achieve lock-freedom.
Chris@16:  *
Chris@16:  *  - \ref boost::lockfree::capacity, optional \n
Chris@16:  *    If this template argument is passed to the options, the size of the queue is set at compile-time.\n
Chris@16:  *    It this option implies \c fixed_sized<true>
Chris@16:  *
Chris@16:  *  - \ref boost::lockfree::allocator, defaults to \c boost::lockfree::allocator<std::allocator<void>> \n
Chris@16:  *    Specifies the allocator that is used for the internal freelist
Chris@16:  *
Chris@16:  *  \b Requirements:
Chris@16:  *   - T must have a copy constructor
Chris@16:  *   - T must have a trivial assignment operator
Chris@16:  *   - T must have a trivial destructor
Chris@16:  *
Chris@16:  * */
Chris@16: #ifndef BOOST_DOXYGEN_INVOKED
Chris@16: template <typename T,
Chris@16:           class A0 = boost::parameter::void_,
Chris@16:           class A1 = boost::parameter::void_,
Chris@16:           class A2 = boost::parameter::void_>
Chris@16: #else
Chris@16: template <typename T, ...Options>
Chris@16: #endif
Chris@16: class queue
Chris@16: {
Chris@16: private:
Chris@16: #ifndef BOOST_DOXYGEN_INVOKED
Chris@16: 
Chris@16: #ifdef BOOST_HAS_TRIVIAL_DESTRUCTOR
Chris@16:     BOOST_STATIC_ASSERT((boost::has_trivial_destructor<T>::value));
Chris@16: #endif
Chris@16: 
Chris@16: #ifdef BOOST_HAS_TRIVIAL_ASSIGN
Chris@16:     BOOST_STATIC_ASSERT((boost::has_trivial_assign<T>::value));
Chris@16: #endif
Chris@16: 
Chris@16:     typedef typename detail::queue_signature::bind<A0, A1, A2>::type bound_args;
Chris@16: 
Chris@16:     static const bool has_capacity = detail::extract_capacity<bound_args>::has_capacity;
Chris@16:     static const size_t capacity = detail::extract_capacity<bound_args>::capacity + 1; // the queue uses one dummy node
Chris@16:     static const bool fixed_sized = detail::extract_fixed_sized<bound_args>::value;
Chris@16:     static const bool node_based = !(has_capacity || fixed_sized);
Chris@16:     static const bool compile_time_sized = has_capacity;
Chris@16: 
Chris@16:     struct BOOST_LOCKFREE_CACHELINE_ALIGNMENT node
Chris@16:     {
Chris@16:         typedef typename detail::select_tagged_handle<node, node_based>::tagged_handle_type tagged_node_handle;
Chris@16:         typedef typename detail::select_tagged_handle<node, node_based>::handle_type handle_type;
Chris@16: 
Chris@16:         node(T const & v, handle_type null_handle):
Chris@16:             data(v)//, next(tagged_node_handle(0, 0))
Chris@16:         {
Chris@16:             /* increment tag to avoid ABA problem */
Chris@16:             tagged_node_handle old_next = next.load(memory_order_relaxed);
Chris@16:             tagged_node_handle new_next (null_handle, old_next.get_next_tag());
Chris@16:             next.store(new_next, memory_order_release);
Chris@16:         }
Chris@16: 
Chris@16:         node (handle_type null_handle):
Chris@16:             next(tagged_node_handle(null_handle, 0))
Chris@16:         {}
Chris@16: 
Chris@16:         node(void)
Chris@16:         {}
Chris@16: 
Chris@16:         atomic<tagged_node_handle> next;
Chris@16:         T data;
Chris@16:     };
Chris@16: 
Chris@16:     typedef typename detail::extract_allocator<bound_args, node>::type node_allocator;
Chris@16:     typedef typename detail::select_freelist<node, node_allocator, compile_time_sized, fixed_sized, capacity>::type pool_t;
Chris@16:     typedef typename pool_t::tagged_node_handle tagged_node_handle;
Chris@16:     typedef typename detail::select_tagged_handle<node, node_based>::handle_type handle_type;
Chris@16: 
Chris@16:     void initialize(void)
Chris@16:     {
Chris@16:         node * n = pool.template construct<true, false>(pool.null_handle());
Chris@16:         tagged_node_handle dummy_node(pool.get_handle(n), 0);
Chris@16:         head_.store(dummy_node, memory_order_relaxed);
Chris@16:         tail_.store(dummy_node, memory_order_release);
Chris@16:     }
Chris@16: 
Chris@16:     struct implementation_defined
Chris@16:     {
Chris@16:         typedef node_allocator allocator;
Chris@16:         typedef std::size_t size_type;
Chris@16:     };
Chris@16: 
Chris@16: #endif
Chris@16: 
Chris@101:     BOOST_DELETED_FUNCTION(queue(queue const&))
Chris@101:     BOOST_DELETED_FUNCTION(queue& operator= (queue const&))
Chris@16: 
Chris@16: public:
Chris@16:     typedef T value_type;
Chris@16:     typedef typename implementation_defined::allocator allocator;
Chris@16:     typedef typename implementation_defined::size_type size_type;
Chris@16: 
Chris@16:     /**
Chris@16:      * \return true, if implementation is lock-free.
Chris@16:      *
Chris@16:      * \warning It only checks, if the queue head and tail nodes and the freelist can be modified in a lock-free manner.
Chris@16:      *       On most platforms, the whole implementation is lock-free, if this is true. Using c++0x-style atomics, there is
Chris@16:      *       no possibility to provide a completely accurate implementation, because one would need to test every internal
Chris@16:      *       node, which is impossible if further nodes will be allocated from the operating system.
Chris@16:      * */
Chris@16:     bool is_lock_free (void) const
Chris@16:     {
Chris@16:         return head_.is_lock_free() && tail_.is_lock_free() && pool.is_lock_free();
Chris@16:     }
Chris@16: 
Chris@16:     //! Construct queue
Chris@16:     // @{
Chris@16:     queue(void):
Chris@16:         head_(tagged_node_handle(0, 0)),
Chris@16:         tail_(tagged_node_handle(0, 0)),
Chris@16:         pool(node_allocator(), capacity)
Chris@16:     {
Chris@16:         BOOST_ASSERT(has_capacity);
Chris@16:         initialize();
Chris@16:     }
Chris@16: 
Chris@16:     template <typename U>
Chris@16:     explicit queue(typename node_allocator::template rebind<U>::other const & alloc):
Chris@16:         head_(tagged_node_handle(0, 0)),
Chris@16:         tail_(tagged_node_handle(0, 0)),
Chris@16:         pool(alloc, capacity)
Chris@16:     {
Chris@16:         BOOST_STATIC_ASSERT(has_capacity);
Chris@16:         initialize();
Chris@16:     }
Chris@16: 
Chris@16:     explicit queue(allocator const & alloc):
Chris@16:         head_(tagged_node_handle(0, 0)),
Chris@16:         tail_(tagged_node_handle(0, 0)),
Chris@16:         pool(alloc, capacity)
Chris@16:     {
Chris@16:         BOOST_ASSERT(has_capacity);
Chris@16:         initialize();
Chris@16:     }
Chris@16:     // @}
Chris@16: 
Chris@16:     //! Construct queue, allocate n nodes for the freelist.
Chris@16:     // @{
Chris@16:     explicit queue(size_type n):
Chris@16:         head_(tagged_node_handle(0, 0)),
Chris@16:         tail_(tagged_node_handle(0, 0)),
Chris@16:         pool(node_allocator(), n + 1)
Chris@16:     {
Chris@16:         BOOST_ASSERT(!has_capacity);
Chris@16:         initialize();
Chris@16:     }
Chris@16: 
Chris@16:     template <typename U>
Chris@16:     queue(size_type n, typename node_allocator::template rebind<U>::other const & alloc):
Chris@16:         head_(tagged_node_handle(0, 0)),
Chris@16:         tail_(tagged_node_handle(0, 0)),
Chris@16:         pool(alloc, n + 1)
Chris@16:     {
Chris@16:         BOOST_STATIC_ASSERT(!has_capacity);
Chris@16:         initialize();
Chris@16:     }
Chris@16:     // @}
Chris@16: 
Chris@16:     /** \copydoc boost::lockfree::stack::reserve
Chris@16:      * */
Chris@16:     void reserve(size_type n)
Chris@16:     {
Chris@16:         pool.template reserve<true>(n);
Chris@16:     }
Chris@16: 
Chris@16:     /** \copydoc boost::lockfree::stack::reserve_unsafe
Chris@16:      * */
Chris@16:     void reserve_unsafe(size_type n)
Chris@16:     {
Chris@16:         pool.template reserve<false>(n);
Chris@16:     }
Chris@16: 
Chris@16:     /** Destroys queue, free all nodes from freelist.
Chris@16:      * */
Chris@16:     ~queue(void)
Chris@16:     {
Chris@16:         T dummy;
Chris@16:         while(unsynchronized_pop(dummy))
Chris@16:         {}
Chris@16: 
Chris@16:         pool.template destruct<false>(head_.load(memory_order_relaxed));
Chris@16:     }
Chris@16: 
Chris@16:     /** Check if the queue is empty
Chris@16:      *
Chris@16:      * \return true, if the queue is empty, false otherwise
Chris@16:      * \note The result is only accurate, if no other thread modifies the queue. Therefore it is rarely practical to use this
Chris@16:      *       value in program logic.
Chris@16:      * */
Chris@101:     bool empty(void) const
Chris@16:     {
Chris@16:         return pool.get_handle(head_.load()) == pool.get_handle(tail_.load());
Chris@16:     }
Chris@16: 
Chris@16:     /** Pushes object t to the queue.
Chris@16:      *
Chris@16:      * \post object will be pushed to the queue, if internal node can be allocated
Chris@16:      * \returns true, if the push operation is successful.
Chris@16:      *
Chris@16:      * \note Thread-safe. If internal memory pool is exhausted and the memory pool is not fixed-sized, a new node will be allocated
Chris@16:      *                    from the OS. This may not be lock-free.
Chris@16:      * */
Chris@16:     bool push(T const & t)
Chris@16:     {
Chris@16:         return do_push<false>(t);
Chris@16:     }
Chris@16: 
Chris@16:     /** Pushes object t to the queue.
Chris@16:      *
Chris@16:      * \post object will be pushed to the queue, if internal node can be allocated
Chris@16:      * \returns true, if the push operation is successful.
Chris@16:      *
Chris@16:      * \note Thread-safe and non-blocking. If internal memory pool is exhausted, operation will fail
Chris@16:      * \throws if memory allocator throws
Chris@16:      * */
Chris@16:     bool bounded_push(T const & t)
Chris@16:     {
Chris@16:         return do_push<true>(t);
Chris@16:     }
Chris@16: 
Chris@16: 
Chris@16: private:
Chris@16: #ifndef BOOST_DOXYGEN_INVOKED
Chris@16:     template <bool Bounded>
Chris@16:     bool do_push(T const & t)
Chris@16:     {
Chris@16:         using detail::likely;
Chris@16: 
Chris@16:         node * n = pool.template construct<true, Bounded>(t, pool.null_handle());
Chris@16:         handle_type node_handle = pool.get_handle(n);
Chris@16: 
Chris@16:         if (n == NULL)
Chris@16:             return false;
Chris@16: 
Chris@16:         for (;;) {
Chris@16:             tagged_node_handle tail = tail_.load(memory_order_acquire);
Chris@16:             node * tail_node = pool.get_pointer(tail);
Chris@16:             tagged_node_handle next = tail_node->next.load(memory_order_acquire);
Chris@16:             node * next_ptr = pool.get_pointer(next);
Chris@16: 
Chris@16:             tagged_node_handle tail2 = tail_.load(memory_order_acquire);
Chris@16:             if (likely(tail == tail2)) {
Chris@16:                 if (next_ptr == 0) {
Chris@16:                     tagged_node_handle new_tail_next(node_handle, next.get_next_tag());
Chris@16:                     if ( tail_node->next.compare_exchange_weak(next, new_tail_next) ) {
Chris@16:                         tagged_node_handle new_tail(node_handle, tail.get_next_tag());
Chris@16:                         tail_.compare_exchange_strong(tail, new_tail);
Chris@16:                         return true;
Chris@16:                     }
Chris@16:                 }
Chris@16:                 else {
Chris@16:                     tagged_node_handle new_tail(pool.get_handle(next_ptr), tail.get_next_tag());
Chris@16:                     tail_.compare_exchange_strong(tail, new_tail);
Chris@16:                 }
Chris@16:             }
Chris@16:         }
Chris@16:     }
Chris@16: #endif
Chris@16: 
Chris@16: public:
Chris@16: 
Chris@16:     /** Pushes object t to the queue.
Chris@16:      *
Chris@16:      * \post object will be pushed to the queue, if internal node can be allocated
Chris@16:      * \returns true, if the push operation is successful.
Chris@16:      *
Chris@16:      * \note Not Thread-safe. If internal memory pool is exhausted and the memory pool is not fixed-sized, a new node will be allocated
Chris@16:      *       from the OS. This may not be lock-free.
Chris@16:      * \throws if memory allocator throws
Chris@16:      * */
Chris@16:     bool unsynchronized_push(T const & t)
Chris@16:     {
Chris@16:         node * n = pool.template construct<false, false>(t, pool.null_handle());
Chris@16: 
Chris@16:         if (n == NULL)
Chris@16:             return false;
Chris@16: 
Chris@16:         for (;;) {
Chris@16:             tagged_node_handle tail = tail_.load(memory_order_relaxed);
Chris@16:             tagged_node_handle next = tail->next.load(memory_order_relaxed);
Chris@16:             node * next_ptr = next.get_ptr();
Chris@16: 
Chris@16:             if (next_ptr == 0) {
Chris@16:                 tail->next.store(tagged_node_handle(n, next.get_next_tag()), memory_order_relaxed);
Chris@16:                 tail_.store(tagged_node_handle(n, tail.get_next_tag()), memory_order_relaxed);
Chris@16:                 return true;
Chris@16:             }
Chris@16:             else
Chris@16:                 tail_.store(tagged_node_handle(next_ptr, tail.get_next_tag()), memory_order_relaxed);
Chris@16:         }
Chris@16:     }
Chris@16: 
Chris@16:     /** Pops object from queue.
Chris@16:      *
Chris@16:      * \post if pop operation is successful, object will be copied to ret.
Chris@16:      * \returns true, if the pop operation is successful, false if queue was empty.
Chris@16:      *
Chris@16:      * \note Thread-safe and non-blocking
Chris@16:      * */
Chris@16:     bool pop (T & ret)
Chris@16:     {
Chris@16:         return pop<T>(ret);
Chris@16:     }
Chris@16: 
Chris@16:     /** Pops object from queue.
Chris@16:      *
Chris@16:      * \pre type U must be constructible by T and copyable, or T must be convertible to U
Chris@16:      * \post if pop operation is successful, object will be copied to ret.
Chris@16:      * \returns true, if the pop operation is successful, false if queue was empty.
Chris@16:      *
Chris@16:      * \note Thread-safe and non-blocking
Chris@16:      * */
Chris@16:     template <typename U>
Chris@16:     bool pop (U & ret)
Chris@16:     {
Chris@16:         using detail::likely;
Chris@16:         for (;;) {
Chris@16:             tagged_node_handle head = head_.load(memory_order_acquire);
Chris@16:             node * head_ptr = pool.get_pointer(head);
Chris@16: 
Chris@16:             tagged_node_handle tail = tail_.load(memory_order_acquire);
Chris@16:             tagged_node_handle next = head_ptr->next.load(memory_order_acquire);
Chris@16:             node * next_ptr = pool.get_pointer(next);
Chris@16: 
Chris@16:             tagged_node_handle head2 = head_.load(memory_order_acquire);
Chris@16:             if (likely(head == head2)) {
Chris@16:                 if (pool.get_handle(head) == pool.get_handle(tail)) {
Chris@16:                     if (next_ptr == 0)
Chris@16:                         return false;
Chris@16: 
Chris@16:                     tagged_node_handle new_tail(pool.get_handle(next), tail.get_next_tag());
Chris@16:                     tail_.compare_exchange_strong(tail, new_tail);
Chris@16: 
Chris@16:                 } else {
Chris@16:                     if (next_ptr == 0)
Chris@16:                         /* this check is not part of the original algorithm as published by michael and scott
Chris@16:                          *
Chris@16:                          * however we reuse the tagged_ptr part for the freelist and clear the next part during node
Chris@16:                          * allocation. we can observe a null-pointer here.
Chris@16:                          * */
Chris@16:                         continue;
Chris@16:                     detail::copy_payload(next_ptr->data, ret);
Chris@16: 
Chris@16:                     tagged_node_handle new_head(pool.get_handle(next), head.get_next_tag());
Chris@16:                     if (head_.compare_exchange_weak(head, new_head)) {
Chris@16:                         pool.template destruct<true>(head);
Chris@16:                         return true;
Chris@16:                     }
Chris@16:                 }
Chris@16:             }
Chris@16:         }
Chris@16:     }
Chris@16: 
Chris@16:     /** Pops object from queue.
Chris@16:      *
Chris@16:      * \post if pop operation is successful, object will be copied to ret.
Chris@16:      * \returns true, if the pop operation is successful, false if queue was empty.
Chris@16:      *
Chris@16:      * \note Not thread-safe, but non-blocking
Chris@16:      *
Chris@16:      * */
Chris@16:     bool unsynchronized_pop (T & ret)
Chris@16:     {
Chris@16:         return unsynchronized_pop<T>(ret);
Chris@16:     }
Chris@16: 
Chris@16:     /** Pops object from queue.
Chris@16:      *
Chris@16:      * \pre type U must be constructible by T and copyable, or T must be convertible to U
Chris@16:      * \post if pop operation is successful, object will be copied to ret.
Chris@16:      * \returns true, if the pop operation is successful, false if queue was empty.
Chris@16:      *
Chris@16:      * \note Not thread-safe, but non-blocking
Chris@16:      *
Chris@16:      * */
Chris@16:     template <typename U>
Chris@16:     bool unsynchronized_pop (U & ret)
Chris@16:     {
Chris@16:         for (;;) {
Chris@16:             tagged_node_handle head = head_.load(memory_order_relaxed);
Chris@16:             node * head_ptr = pool.get_pointer(head);
Chris@16:             tagged_node_handle tail = tail_.load(memory_order_relaxed);
Chris@16:             tagged_node_handle next = head_ptr->next.load(memory_order_relaxed);
Chris@16:             node * next_ptr = pool.get_pointer(next);
Chris@16: 
Chris@16:             if (pool.get_handle(head) == pool.get_handle(tail)) {
Chris@16:                 if (next_ptr == 0)
Chris@16:                     return false;
Chris@16: 
Chris@16:                 tagged_node_handle new_tail(pool.get_handle(next), tail.get_next_tag());
Chris@16:                 tail_.store(new_tail);
Chris@16:             } else {
Chris@16:                 if (next_ptr == 0)
Chris@16:                     /* this check is not part of the original algorithm as published by michael and scott
Chris@16:                      *
Chris@16:                      * however we reuse the tagged_ptr part for the freelist and clear the next part during node
Chris@16:                      * allocation. we can observe a null-pointer here.
Chris@16:                      * */
Chris@16:                     continue;
Chris@16:                 detail::copy_payload(next_ptr->data, ret);
Chris@16:                 tagged_node_handle new_head(pool.get_handle(next), head.get_next_tag());
Chris@16:                 head_.store(new_head);
Chris@16:                 pool.template destruct<false>(head);
Chris@16:                 return true;
Chris@16:             }
Chris@16:         }
Chris@16:     }
Chris@16: 
Chris@16:     /** consumes one element via a functor
Chris@16:      *
Chris@16:      *  pops one element from the queue and applies the functor on this object
Chris@16:      *
Chris@16:      * \returns true, if one element was consumed
Chris@16:      *
Chris@16:      * \note Thread-safe and non-blocking, if functor is thread-safe and non-blocking
Chris@16:      * */
Chris@16:     template <typename Functor>
Chris@16:     bool consume_one(Functor & f)
Chris@16:     {
Chris@16:         T element;
Chris@16:         bool success = pop(element);
Chris@16:         if (success)
Chris@16:             f(element);
Chris@16: 
Chris@16:         return success;
Chris@16:     }
Chris@16: 
Chris@16:     /// \copydoc boost::lockfree::queue::consume_one(Functor & rhs)
Chris@16:     template <typename Functor>
Chris@16:     bool consume_one(Functor const & f)
Chris@16:     {
Chris@16:         T element;
Chris@16:         bool success = pop(element);
Chris@16:         if (success)
Chris@16:             f(element);
Chris@16: 
Chris@16:         return success;
Chris@16:     }
Chris@16: 
Chris@16:     /** consumes all elements via a functor
Chris@16:      *
Chris@16:      * sequentially pops all elements from the queue and applies the functor on each object
Chris@16:      *
Chris@16:      * \returns number of elements that are consumed
Chris@16:      *
Chris@16:      * \note Thread-safe and non-blocking, if functor is thread-safe and non-blocking
Chris@16:      * */
Chris@16:     template <typename Functor>
Chris@16:     size_t consume_all(Functor & f)
Chris@16:     {
Chris@16:         size_t element_count = 0;
Chris@16:         while (consume_one(f))
Chris@16:             element_count += 1;
Chris@16: 
Chris@16:         return element_count;
Chris@16:     }
Chris@16: 
Chris@16:     /// \copydoc boost::lockfree::queue::consume_all(Functor & rhs)
Chris@16:     template <typename Functor>
Chris@16:     size_t consume_all(Functor const & f)
Chris@16:     {
Chris@16:         size_t element_count = 0;
Chris@16:         while (consume_one(f))
Chris@16:             element_count += 1;
Chris@16: 
Chris@16:         return element_count;
Chris@16:     }
Chris@16: 
Chris@16: private:
Chris@16: #ifndef BOOST_DOXYGEN_INVOKED
Chris@16:     atomic<tagged_node_handle> head_;
Chris@16:     static const int padding_size = BOOST_LOCKFREE_CACHELINE_BYTES - sizeof(tagged_node_handle);
Chris@16:     char padding1[padding_size];
Chris@16:     atomic<tagged_node_handle> tail_;
Chris@16:     char padding2[padding_size];
Chris@16: 
Chris@16:     pool_t pool;
Chris@16: #endif
Chris@16: };
Chris@16: 
Chris@16: } /* namespace lockfree */
Chris@16: } /* namespace boost */
Chris@16: 
Chris@16: #if defined(_MSC_VER)
Chris@16: #pragma warning(pop)
Chris@16: #endif
Chris@16: 
Chris@16: #endif /* BOOST_LOCKFREE_FIFO_HPP_INCLUDED */