RakNet/DependentExtensions/cat/threads/LocklessFIFO.hpp

/*
	Copyright (c) 2009-2010 Christopher A. Taylor.  All rights reserved.

	Redistribution and use in source and binary forms, with or without
	modification, are permitted provided that the following conditions are met:

	* Redistributions of source code must retain the above copyright notice,
	  this list of conditions and the following disclaimer.
	* Redistributions in binary form must reproduce the above copyright notice,
	  this list of conditions and the following disclaimer in the documentation
	  and/or other materials provided with the distribution.
	* Neither the name of LibCat nor the names of its contributors may be used
	  to endorse or promote products derived from this software without
	  specific prior written permission.

	THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
	LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	POSSIBILITY OF SUCH DAMAGE.
*/

/*
    Algorithm from "An Optimistic Approach to Lock-Free FIFO Queues"
        Edya Ladan-Mozes and Nir Shavit (2004)
*/

#ifndef CAT_LOCKLESS_FIFO_HPP
#define CAT_LOCKLESS_FIFO_HPP

#include <cat/threads/RegionAllocator.hpp>
#include <cat/threads/Atomic.hpp>

#if defined(CAT_OS_WINDOWS)
# include <cat/port/WindowsInclude.hpp>
#else
# error "Not portable to your OS!"
#endif

namespace cat {


namespace FIFO {

template<class T> class Ptr;
template<class T> class Node;
template<class T> class Queue;


//// Ptr

    // Union for an ABA-proof pointer
    template<class T>
    class Ptr
    {
    public:
        union
        {
            struct
            {
                Node<T> *ptr;
#if defined(CAT_WORD_64)
                u64 tag;
#else
                u32 tag;
#endif
            };
#if defined(CAT_WORD_64)
            volatile u64 N[2];
#else
            volatile u64 N;
#endif
        } CAT_PACKED;

        Ptr(); // zero everything

        bool operator==(const Ptr<T> &rhs);
        bool operator!=(const Ptr<T> &rhs);
    };


//// Derive from Data<T> for data passed through the queue

    template<class T>
    class Node
    {
        friend class Queue<T>;

        T *value;
        Ptr<T> next, prev;
    };


//// Queue

    // Performs lazy deallocation of data objects on behalf of the caller,
    // freeing all remaining objects when the Queue goes out of scope.
    template<class T>
    class Queue
    {
        // Pointer to head and tail
        Ptr<T> Head, Tail;

        // Event to wait on if dequeuing
#if defined(CAT_OS_WINDOWS)
        HANDLE hEvent;
#endif

    public:
        Queue();
        ~Queue();

    public:
        void Enqueue(T *data);
        T *Dequeue();
        void FixList(Ptr<T> tail, Ptr<T> head);

        // Enqueue a new event to wake up a thread stuck here
        T *DequeueWait();
    };


//// Compare-and-Swap x2 (CAS2) atomic operation

    template<class T>
    inline bool CAS2(Ptr<T> &destination, const Ptr<T> &expected, const Ptr<T> &replacement)
    {
        return Atomic::CAS2(&destination, &expected, &replacement);
    }


//// Ptr: Templated member implementation

    template<class T>
    Ptr<T>::Ptr()
    {
#if defined(CAT_WORD_64)
        N[0] = 0;
        N[1] = 0;
#else
        N = 0;
#endif
    }

    template<class T>
    bool Ptr<T>::operator==(const Ptr<T> &n)
    {
#if defined(CAT_WORD_64)
        return N[0] == n.N[0] && N[1] == n.N[1];
#else
        return N == n.N;
#endif
    }

    template<class T>
    bool Ptr<T>::operator!=(const Ptr<T> &n)
    {
#if defined(CAT_WORD_64)
        return N[0] != n.N[0] || N[1] != n.N[1];
#else
        return N != n.N;
#endif
    }


//// Queue: Templated member implementation

    template<class T>
    Queue<T>::Queue()
    {
#if defined(CAT_OS_WINDOWS)
        hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
#endif

        Node<T> *node = new (RegionAllocator::ii) Node<T>;
        node->value = 0;

        Head.ptr = Tail.ptr = node;
    }

    template<class T>
    Queue<T>::~Queue()
    {
        // Destroy objects that are still queued
        for (Node<T> *next, *ptr = Head.ptr; ptr; ptr = next)
        {
            next = ptr->next.ptr;

            if (ptr->value)
                RegionAllocator::ii->Delete(ptr->value);
            RegionAllocator::ii->Delete(ptr);
        }

#if defined(CAT_OS_WINDOWS)
        CloseHandle(hEvent);
#endif
    }

    template<class T>
    void Queue<T>::Enqueue(T *val)
    {
        Ptr<T> tail;
        Node<T> *nd = new (RegionAllocator::ii) Node<T>;
        nd->value = val;

        for (;;)
        {
            tail = Tail;
            nd->next.ptr = tail.ptr;
            nd->next.tag = tail.tag + 1;

            Ptr<T> new_tail;
            new_tail.ptr = nd;
            new_tail.tag = tail.tag + 1;

            if (CAS2(Tail, tail, new_tail))
            {
                tail.ptr->prev.ptr = nd;
                tail.ptr->prev.tag = tail.tag;
                break;
            }
        }

#if defined(CAT_OS_WINDOWS)
        SetEvent(hEvent);
#endif
    }

    template<class T>
    T *Queue<T>::DequeueWait()
    {
        for (;;)
        {
            // Attempt to dequeue a message
            // If we won the race to service the message, then return it
            T *retval = Dequeue();
            if (retval) return retval;

#if defined(CAT_OS_WINDOWS)
            // If the sychronization wait fails (handle closed), abort with 0
            if (WaitForSingleObject(hEvent, INFINITE) != WAIT_OBJECT_0)
                return 0;
#endif
        }
    }

    template<class T>
    T *Queue<T>::Dequeue()
    {
        Ptr<T> tail, head, firstNodePrev;
        Node<T> *nd_dummy;
        T *val;

        for (;;)
        {
            head = Head;
            tail = Tail;
            firstNodePrev = head.ptr->prev;
            val = head.ptr->value;

            if (head == Head)
            {
                if (val != 0)
                {
                    if (tail != head)
                    {
                        if (firstNodePrev.tag != head.tag)
                        {
                            FixList(tail, head);
                            continue;
                        }
                    }
                    else
                    {
                        nd_dummy = new (RegionAllocator::ii) Node<T>;
                        nd_dummy->value = 0;
                        nd_dummy->next.ptr = tail.ptr;
                        nd_dummy->next.tag = tail.tag + 1;

                        Ptr<T> new_tail;
                        new_tail.ptr = nd_dummy;
                        new_tail.tag = tail.tag + 1;

                        if (CAS2(Tail, tail, new_tail))
                        {
                            head.ptr->prev.ptr = nd_dummy;
                            head.ptr->prev.tag = tail.tag;
                        }
                        else
                        {
                            RegionAllocator::ii->Delete(nd_dummy);
                        }

                        continue;
                    }

                    Ptr<T> new_head;
                    new_head.ptr = firstNodePrev.ptr;
                    new_head.tag = head.tag + 1;

                    if (CAS2(Head, head, new_head))
                    {
                        RegionAllocator::ii->Delete(head.ptr);
                        return val;
                    }
                }
                else
                {
                    if (tail.ptr == head.ptr)
                        return 0;

                    if (firstNodePrev.tag != head.tag)
                    {
                        FixList(tail, head);

                        continue;
                    }

                    Ptr<T> new_head;
                    new_head.ptr = firstNodePrev.ptr;
                    new_head.tag = head.tag + 1;

                    CAS2(Head, head, new_head);
                }
            }
        }
    }

    template<class T>
    void Queue<T>::FixList(Ptr<T> tail, Ptr<T> head)
    {
        Ptr<T> curNode, curNodeNext, nextNodePrev;

        curNode = tail;

        while (head == Head && curNode != head)
        {
            curNodeNext = curNode.ptr->next;

            if (curNodeNext.tag != curNode.tag)
                return;

            nextNodePrev = curNodeNext.ptr->prev;

            if (nextNodePrev.ptr != curNode.ptr || nextNodePrev.tag != curNode.tag - 1)
            {
                curNodeNext.ptr->prev.ptr = curNode.ptr;
                curNodeNext.ptr->prev.tag = curNode.tag - 1;
            }

            curNode.ptr = curNodeNext.ptr;
            curNode.tag = curNode.tag - 1;
        }
    }


} // namespace FIFO


} // namespace cat

#endif // CAT_LOCKLESS_FIFO_HPP