boost/lockfree/queue.hpp
// 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 #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> #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 * It 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 * * */ #ifndef BOOST_DOXYGEN_INVOKED template <typename T, class A0 = boost::parameter::void_, class A1 = boost::parameter::void_, class A2 = boost::parameter::void_> #else template <typename T, ...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 typedef typename detail::queue_signature::bind<A0, A1, A2>::type bound_args; 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_LOCKFREE_CACHELINE_ALIGNMENT 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): data(v)//, next(tagged_node_handle(0, 0)) { /* 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 */