vcompactingdeque.h

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/*
Copyright c1997-2014 Trygve Isaacson. All rights reserved.
This file is part of the Code Vault version 4.1
http://www.bombaydigital.com/
License: MIT. See LICENSE.md in the Vault top level directory.
*/

#ifndef vcompactingdeque_h
#define vcompactingdeque_h

#include "vtypes.h"

template < typename _Tp, typename _Alloc = std::allocator<_Tp> >
class VCompactingDeque : public std::deque<_Tp, _Alloc> {
    public:

        VCompactingDeque(size_t highWaterMarkRequired = 64, size_t lowWaterMarkRequired = 0)
            : std::deque<_Tp, _Alloc>()
            , mHighWaterMark(0)
            , mHighWaterMarkRequired(highWaterMarkRequired)
            , mLowWaterMarkRequired(lowWaterMarkRequired)
            {}
        ~VCompactingDeque() {}

        void pop_front() {
            this->_saveHighWaterMark();

            std::deque<_Tp, _Alloc>::pop_front();

            this->_compactIfReachedThreshold();
        }

        void pop_back() {
            this->_saveHighWaterMark();

            std::deque<_Tp, _Alloc>::pop_back();

            this->_compactIfReachedThreshold();
        }

        void compact() { this->_compact(); }

    private:

        void _saveHighWaterMark() {
            mHighWaterMark = V_MAX(mHighWaterMark, this->size());
        }

        void _compactIfReachedThreshold() {
            if ((mHighWaterMark >= mHighWaterMarkRequired) && (this->size() <= mLowWaterMarkRequired)) {
                this->_compact();
            }
        }

        void _compact() {
            // See: http://www.gotw.ca/gotw/054.htm for details. Swap causes a fairly efficient copy to a fresh data structure.
            std::deque<_Tp, _Alloc> temp(*this);
            temp.swap(*this);
            mHighWaterMark = 0; // Doesn't mean current size is zero, means previous hwm is obsolete.
        }

        size_t mHighWaterMark;          
        size_t mHighWaterMarkRequired;  
        size_t mLowWaterMarkRequired;   

        friend class VMessageUnit; // Unit test can peek at our internal state between operations.
};

#endif /* vcompactingdeque_h */