Rearrange sources (#4997)

include/xrpl/beast/core/LockFreeStack.h

@@ -0,0 +1,307 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of Beast: https://github.com/vinniefalco/Beast
+    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef BEAST_INTRUSIVE_LOCKFREESTACK_H_INCLUDED
+#define BEAST_INTRUSIVE_LOCKFREESTACK_H_INCLUDED
+
+#include <atomic>
+#include <iterator>
+#include <type_traits>
+
+namespace beast {
+
+//------------------------------------------------------------------------------
+
+template <class Container, bool IsConst>
+class LockFreeStackIterator
+{
+protected:
+    using Node = typename Container::Node;
+    using NodePtr =
+        typename std::conditional<IsConst, Node const*, Node*>::type;
+
+public:
+    using iterator_category = std::forward_iterator_tag;
+    using value_type = typename Container::value_type;
+    using difference_type = typename Container::difference_type;
+    using pointer = typename std::conditional<
+        IsConst,
+        typename Container::const_pointer,
+        typename Container::pointer>::type;
+    using reference = typename std::conditional<
+        IsConst,
+        typename Container::const_reference,
+        typename Container::reference>::type;
+
+    LockFreeStackIterator() : m_node()
+    {
+    }
+
+    LockFreeStackIterator(NodePtr node) : m_node(node)
+    {
+    }
+
+    template <bool OtherIsConst>
+    explicit LockFreeStackIterator(
+        LockFreeStackIterator<Container, OtherIsConst> const& other)
+        : m_node(other.m_node)
+    {
+    }
+
+    LockFreeStackIterator&
+    operator=(NodePtr node)
+    {
+        m_node = node;
+        return static_cast<LockFreeStackIterator&>(*this);
+    }
+
+    LockFreeStackIterator&
+    operator++()
+    {
+        m_node = m_node->m_next.load();
+        return static_cast<LockFreeStackIterator&>(*this);
+    }
+
+    LockFreeStackIterator
+    operator++(int)
+    {
+        LockFreeStackIterator result(*this);
+        m_node = m_node->m_next;
+        return result;
+    }
+
+    NodePtr
+    node() const
+    {
+        return m_node;
+    }
+
+    reference
+    operator*() const
+    {
+        return *this->operator->();
+    }
+
+    pointer
+    operator->() const
+    {
+        return static_cast<pointer>(m_node);
+    }
+
+private:
+    NodePtr m_node;
+};
+
+//------------------------------------------------------------------------------
+
+template <class Container, bool LhsIsConst, bool RhsIsConst>
+bool
+operator==(
+    LockFreeStackIterator<Container, LhsIsConst> const& lhs,
+    LockFreeStackIterator<Container, RhsIsConst> const& rhs)
+{
+    return lhs.node() == rhs.node();
+}
+
+template <class Container, bool LhsIsConst, bool RhsIsConst>
+bool
+operator!=(
+    LockFreeStackIterator<Container, LhsIsConst> const& lhs,
+    LockFreeStackIterator<Container, RhsIsConst> const& rhs)
+{
+    return lhs.node() != rhs.node();
+}
+
+//------------------------------------------------------------------------------
+
+/** Multiple Producer, Multiple Consumer (MPMC) intrusive stack.
+
+    This stack is implemented using the same intrusive interface as List.
+    All mutations are lock-free.
+
+    The caller is responsible for preventing the "ABA" problem:
+        http://en.wikipedia.org/wiki/ABA_problem
+
+    @param Tag  A type name used to distinguish lists and nodes, for
+                putting objects in multiple lists. If this parameter is
+                omitted, the default tag is used.
+*/
+template <class Element, class Tag = void>
+class LockFreeStack
+{
+public:
+    class Node
+    {
+    public:
+        Node() : m_next(nullptr)
+        {
+        }
+
+        explicit Node(Node* next) : m_next(next)
+        {
+        }
+
+        Node(Node const&) = delete;
+        Node&
+        operator=(Node const&) = delete;
+
+    private:
+        friend class LockFreeStack;
+
+        template <class Container, bool IsConst>
+        friend class LockFreeStackIterator;
+
+        std::atomic<Node*> m_next;
+    };
+
+public:
+    using value_type = Element;
+    using pointer = Element*;
+    using reference = Element&;
+    using const_pointer = Element const*;
+    using const_reference = Element const&;
+    using size_type = std::size_t;
+    using difference_type = std::ptrdiff_t;
+    using iterator = LockFreeStackIterator<LockFreeStack<Element, Tag>, false>;
+    using const_iterator =
+        LockFreeStackIterator<LockFreeStack<Element, Tag>, true>;
+
+    LockFreeStack() : m_end(nullptr), m_head(&m_end)
+    {
+    }
+
+    LockFreeStack(LockFreeStack const&) = delete;
+    LockFreeStack&
+    operator=(LockFreeStack const&) = delete;
+
+    /** Returns true if the stack is empty. */
+    bool
+    empty() const
+    {
+        return m_head.load() == &m_end;
+    }
+
+    /** Push a node onto the stack.
+        The caller is responsible for preventing the ABA problem.
+        This operation is lock-free.
+        Thread safety:
+            Safe to call from any thread.
+
+        @param node The node to push.
+
+        @return `true` if the stack was previously empty. If multiple threads
+                are attempting to push, only one will receive `true`.
+    */
+    // VFALCO NOTE Fix this, shouldn't it be a reference like intrusive list?
+    bool
+    push_front(Node* node)
+    {
+        bool first;
+        Node* old_head = m_head.load(std::memory_order_relaxed);
+        do
+        {
+            first = (old_head == &m_end);
+            node->m_next = old_head;
+        } while (!m_head.compare_exchange_strong(
+            old_head,
+            node,
+            std::memory_order_release,
+            std::memory_order_relaxed));
+        return first;
+    }
+
+    /** Pop an element off the stack.
+        The caller is responsible for preventing the ABA problem.
+        This operation is lock-free.
+        Thread safety:
+            Safe to call from any thread.
+
+        @return The element that was popped, or `nullptr` if the stack
+                was empty.
+    */
+    Element*
+    pop_front()
+    {
+        Node* node = m_head.load();
+        Node* new_head;
+        do
+        {
+            if (node == &m_end)
+                return nullptr;
+            new_head = node->m_next.load();
+        } while (!m_head.compare_exchange_strong(
+            node,
+            new_head,
+            std::memory_order_release,
+            std::memory_order_relaxed));
+        return static_cast<Element*>(node);
+    }
+
+    /** Return a forward iterator to the beginning or end of the stack.
+        Undefined behavior results if push_front or pop_front is called
+        while an iteration is in progress.
+        Thread safety:
+            Caller is responsible for synchronization.
+    */
+    /** @{ */
+    iterator
+    begin()
+    {
+        return iterator(m_head.load());
+    }
+
+    iterator
+    end()
+    {
+        return iterator(&m_end);
+    }
+
+    const_iterator
+    begin() const
+    {
+        return const_iterator(m_head.load());
+    }
+
+    const_iterator
+    end() const
+    {
+        return const_iterator(&m_end);
+    }
+
+    const_iterator
+    cbegin() const
+    {
+        return const_iterator(m_head.load());
+    }
+
+    const_iterator
+    cend() const
+    {
+        return const_iterator(&m_end);
+    }
+    /** @} */
+
+private:
+    Node m_end;
+    std::atomic<Node*> m_head;
+};
+
+}  // namespace beast
+
+#endif