LocklessFIFO.hpp

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/*
    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
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*/

/*
    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;



    // 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);
    };



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

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



    // 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();
    };



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



    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
    }



    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