/*============================================================================*/
/*
  VFLib: https://github.com/vinniefalco/VFLib

  Copyright (C) 2008 by Vinnie Falco <vinnie.falco@gmail.com>

  This library contains portions of other open source products covered by
  separate licenses. Please see the corresponding source files for specific
  terms.

  VFLib is provided under the terms of The MIT License (MIT):

  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  IN THE SOFTWARE.
*/
/*============================================================================*/

#ifndef BEAST_LOCKFREESTACK_BEASTHEADER
#define BEAST_LOCKFREESTACK_BEASTHEADER

#include "../memory/beast_AtomicPointer.h"

struct LockFreeStackDefaultTag;

/*============================================================================*/
/**
  Multiple Producer, Multiple Consumer (MPMC) intrusive stack.

  This stack is implemented using the same intrusive interface as List. All
  operations 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.

  @ingroup beast_core intrusive
*/
template <class Element, class Tag = LockFreeStackDefaultTag>
class LockFreeStack : Uncopyable
{
public:
    class Node : Uncopyable
    {
    public:
        Node ()
        {
        }

        explicit Node (Node* next) : m_next (next)
        {
        }

    private:
        friend class LockFreeStack;

        AtomicPointer <Node> m_next;
    };

public:
    LockFreeStack () : m_head (0)
    {
    }

    /** Create a LockFreeStack from another stack.

        The contents of the other stack are atomically acquired.
        The other stack is cleared.

        @param other  The other stack to acquire.
    */
    explicit LockFreeStack (LockFreeStack& other)
    {
        Node* head;

        do
        {
            head = other.m_head.get ();
        }
        while (!other.m_head.compareAndSet (0, head));

        m_head = head;
    }

    /** Push a node onto the stack.

        The caller is responsible for preventing the ABA problem. This operation
        is lock-free.

        @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.
    */
    bool push_front (Node* node)
    {
        bool first;
        Node* head;

        do
        {
            head = m_head.get ();
            first = head == 0;
            node->m_next = head;
        }
        while (!m_head.compareAndSet (node, head));

        return first;
    }

    /** Pop an element off the stack.

        The caller is responsible for preventing the ABA problem. This operation
        is lock-free.

        @return   The element that was popped, or nullptr if the stack was empty.
    */
    Element* pop_front ()
    {
        Node* node;
        Node* head;

        do
        {
            node = m_head.get ();

            if (node == 0)
                break;

            head = node->m_next.get ();
        }
        while (!m_head.compareAndSet (head, node));

        return node ? static_cast <Element*> (node) : nullptr;
    }

    /** Swap the contents of this stack with another stack.

        This call is not thread safe or atomic. The caller is responsible for
        synchronizing access.

        @param other  The other stack to swap contents with.
    */
    void swap (LockFreeStack& other)
    {
        Node* temp = other.m_head.get ();
        other.m_head.set (m_head.get ());
        m_head.set (temp);
    }

private:
    AtomicPointer <Node> m_head;
};

/*============================================================================*/
/** Default tag for LockFreeStack

    @ingroup beast_core intrusive
*/
struct LockFreeStackDefaultTag { };

#endif