cache.hpp

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/*********************************************************************/
// dar - disk archive - a backup/restoration program
// Copyright (C) 2002-2024 Denis Corbin
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
//
// to contact the author, see the AUTHOR file
/*********************************************************************/
 
 
#ifndef CACHE_HPP
#define CACHE_HPP
 
#include "../my_config.h"
#include "infinint.hpp"
#include "generic_file.hpp"
 
namespace libdar
{
 
 
 
    class cache : public generic_file
    {
    public:
    cache(generic_file & hidden,              
          bool shift_mode,                    
          U_I size = 102400                   
        );
    cache(const cache & ref) = delete;
    cache(cache && ref) = delete;
    cache & operator = (const cache & ref) = delete;
    cache & operator = (cache && ref) = delete;
    ~cache();
    void change_to_read_write() { if(get_mode() == gf_read_only) throw SRC_BUG; set_mode(gf_read_write); };
 
        // inherited from generic_file
 
    virtual bool skippable(skippability direction, const infinint & amount) override;
    virtual bool skip(const infinint & pos) override;
    virtual bool skip_to_eof() override;
    virtual bool skip_relative(S_I x) override;
    virtual bool truncatable(const infinint & pos) const override;
    virtual infinint get_position() const override { return buffer_offset + next; };
 
    protected:
        // inherited from generic_file
    virtual void inherited_read_ahead(const infinint & amount) override;
    virtual U_I inherited_read(char *a, U_I size) override;
    virtual void inherited_write(const char *a, U_I size) override;
    virtual void inherited_truncate(const infinint & pos) override;
    virtual void inherited_sync_write() override { flush_write(); };
    virtual void inherited_flush_read() override { flush_write(); clear_buffer(); };
    virtual void inherited_terminate() override { flush_write(); };
 
    private:
    generic_file *ref;                
    char *buffer;                     
    U_I size;                         
    U_I half;                         
    U_I next;                         
    U_I last;                         
    U_I first_to_write;               
    infinint buffer_offset;           
    bool shifted_mode;                
    infinint eof_offset;              
 
    bool need_flush_write() const { return first_to_write < last; };
    void alloc_buffer(size_t x_size); 
    void release_buffer();            
    void shift_by_half();
    void clear_buffer();
    void flush_write();
    void fulfill_read();
    U_I available_in_cache(skippability direction) const;
    };
 
 
} // end of namespace
 
#endif