BufferLockFree.hpp

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/***************************************************************************
  tag: Peter Soetens  Thu Jan 13 10:24:51 CET 2005  BufferLockFree.hpp

                        BufferLockFree.hpp -  description
                           -------------------
    begin                : Thu January 13 2005
    copyright            : (C) 2005 Peter Soetens
    email                : peter.soetens@mech.kuleuven.ac.be

 ***************************************************************************
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#ifndef ORO_BUFFER_LOCK_FREE_HPP
#define ORO_BUFFER_LOCK_FREE_HPP

#include "../os/oro_arch.h"
#include "../os/Atomic.hpp"
#include "../os/CAS.hpp"
#include "BufferInterface.hpp"
#include "../internal/AtomicMWSRQueue.hpp"
#include "../internal/TsPool.hpp"
#include <vector>

#ifdef ORO_PRAGMA_INTERFACE
#pragma interface
#endif

namespace RTT
{ namespace base {


    using os::CAS;

    template< class T>
    class BufferLockFree
        : public BufferInterface<T>
    {
    public:
        typedef typename BufferInterface<T>::reference_t reference_t;
        typedef typename BufferInterface<T>::param_t param_t;
        typedef typename BufferInterface<T>::size_type size_type;
        typedef T value_t;
    private:
        typedef T Item;
        internal::AtomicMWSRQueue<Item*> bufs;
        // is mutable because of reference counting.
        mutable internal::TsPool<Item> mpool;
        const bool mcircular;
        RTT::os::AtomicInt droppedSamples;
        
    public:
        BufferLockFree( unsigned int bufsize, const T& initial_value = T(), bool circular = false)
            : bufs( bufsize ), mpool(bufsize + 1), mcircular(circular), droppedSamples(0)
        {
            mpool.data_sample( initial_value );
        }

        ~BufferLockFree() {
            // free all items still in the buffer.
            clear();
        }

        virtual void data_sample( const T& sample )
        {
            mpool.data_sample(sample);
        }

        virtual T data_sample() const
        {
            T result = T();
            Item* mitem = mpool.allocate();
            if (mitem != 0) {
                result = *mitem;
                mpool.deallocate( mitem );
            }
            return result;
        }


        size_type capacity() const
        {
            return bufs.capacity();
        }

        size_type size() const
        {
            return bufs.size();
        }

        bool empty() const
        {
            return bufs.isEmpty();
        }

        bool full() const
        {
            return bufs.isFull();
        }

        void clear()
        {
            Item* item;
            while ( bufs.dequeue(item) )
                mpool.deallocate( item );
        }

        virtual size_type dropped() const
        {
            return droppedSamples.read();
        }
        
        bool Push( param_t item)
        {
            if ( capacity() == (size_type)bufs.size() ) {
                if (!mcircular) {
                    droppedSamples.inc();
                    return false;
                }
                // we will recover below in case of circular
            }
            Item* mitem = mpool.allocate();
            if ( mitem == 0 ) { // queue full ( rare but possible in race with PopWithoutRelease )
                if (!mcircular) {
                    droppedSamples.inc();
                    return false;
                }
                else {
                    if (bufs.dequeue( mitem ) == false ) {
                        droppedSamples.inc();
                        return false; // assert(false) ???
                    }
                    // we keep mitem to write item to next
                }
            }

            // copy over.
            *mitem = item;
            if (bufs.enqueue( mitem ) == false ) {
                //got memory, but buffer is full
                //this can happen, as the memory pool is
                //bigger than the buffer
                if (!mcircular) {
                    mpool.deallocate( mitem );
                    droppedSamples.inc();
                    return false;
                } else {
                    // pop & deallocate until we have free space.
                    Item* itmp = 0;
                    do {
                        if ( bufs.dequeue( itmp ) ) {
                            mpool.deallocate( itmp );
                            droppedSamples.inc();
                        } else {
                            // Both operations, enqueue() and dequeue() failed on the buffer:
                            // We could free the allocated pool item return false here,
                            // but in fact this can only happen during massive concurrent
                            // access to the circular buffer or in the trivial case that
                            // the buffer size is zero. So just keep on trying...
                        }
                    } while ( bufs.enqueue( mitem ) == false );
                }
            }
            return true;
        }

        size_type Push(const std::vector<T>& items)
        {
            // @todo Make this function more efficient as in BufferLocked.
            int towrite  = items.size();
            size_type written = 0;
            typename std::vector<T>::const_iterator it;
            for(  it = items.begin(); it != items.end(); ++it) {
                if ( this->Push( *it ) == false ) {
                    break; // will only happen in non-circular case !
                }
                written++;
            }
            droppedSamples.add(towrite - written);
            return written;
        }


        bool Pop( reference_t item )
        {
            Item* ipop;
            if (bufs.dequeue( ipop ) == false )
                return false;
            item = *ipop;
            if (mpool.deallocate( ipop ) == false )
                assert(false);
            return true;
        }

        size_type Pop(std::vector<T>& items )
        {
            Item* ipop;
            items.clear();
            while( bufs.dequeue(ipop) ) {
                items.push_back( *ipop );
                if (mpool.deallocate(ipop) == false)
                    assert(false);
            }
            return items.size();
        }
        
        value_t* PopWithoutRelease()
    {
            Item* ipop;
            if (bufs.dequeue( ipop ) == false )
                return 0;
        return ipop;
    }

    void Release(value_t *item) 
    {
            if (mpool.deallocate( item ) == false )
                assert(false);  
    }
    };
}}

#endif