cache.hpp

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00001 /*********************************************************************/
00002 // dar - disk archive - a backup/restoration program
00003 // Copyright (C) 2002-2052 Denis Corbin
00004 //
00005 // This program is free software; you can redistribute it and/or
00006 // modify it under the terms of the GNU General Public License
00007 // as published by the Free Software Foundation; either version 2
00008 // of the License, or (at your option) any later version.
00009 //
00010 // This program is distributed in the hope that it will be useful,
00011 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00012 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00013 // GNU General Public License for more details.
00014 //
00015 // You should have received a copy of the GNU General Public License
00016 // along with this program; if not, write to the Free Software
00017 // Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
00018 //
00019 // to contact the author : dar.linux@free.fr
00020 /*********************************************************************/
00021 // $Id: cache.hpp,v 1.10 2005/04/09 21:43:34 edrusb Rel $
00022 //
00023 /*********************************************************************/
00024 
00028 
00029 #ifndef CACHE_HPP
00030 #define CACHE_HPP
00031 
00032 #include "../my_config.h"
00033 #include "infinint.hpp"
00034 #include "generic_file.hpp"
00035 
00036 namespace libdar
00037 {
00039 
00050     class cache : public generic_file
00051     {
00052     public:
00053         cache(user_interaction & dialog,
00054               generic_file & hidden,
00055               U_I initial_size = 10240,
00056               U_I unused_read_ratio = 10, U_I observation_read_number = 100, U_I max_size_hit_read_ratio = 50,
00057               U_I unused_write_ratio = 10, U_I observation_write_number = 100, U_I max_size_hit_write_ratio = 50);
00058             // *** hidden: is the file to cache, it is never deleted by the cache object,
00059             // *** intial_size: is the initial size of the cache for reading (read this amount of data at a time)
00060             // unused_read_ratio: is the ratio of cached data effectively asked for reading below which the cache size is divided by two
00061             //   in other words, if during observation_read_number fullfilment of the cache, less than unused_read_ratio percent of data has been
00062             //   effectively asked for reading, then the cache size is divided by two
00063             // *** max_size_hit_read_ratio: is the ratio above which the cache size is doubled. In other words, if during observation_read_number
00064             //   times of cache fullfilment, more than max_size_hit_read_ratio percent time all the cached data has been asked for reading
00065             //   the cache size is doubled.
00066             // to have fixed size read caching, you can set unused_read_ratio to zero and max_size_hit_read_ratio to 101 or above.
00067             // *** unused_write_ratio: cache is flushed before being fullfilled if a seek operation has been asked. If after observation_write_number
00068             //   of cache flushing, less than unused_write_ratio percent of the time the cache was full, its size is divided by 2
00069             // *** max_size_hit_write_ratio: if after observation_write_number of cache flushing, max_size_hit_write_ratio percent of the time
00070             // the cache was fulled, its size get doubled.
00071             // to have a fixed size write caching , you can set unused_write_ratio to zero and max_size_hit_write_ratio to 101 or above
00072         ~cache() { flush_write(); };
00073 
00074 
00075             // inherited from generic_file
00076         bool skip(const infinint & pos) { flush_write(); clear_read(); return ref->skip(pos); };
00077         bool skip_to_eof() { flush_write(); clear_read(); return ref->skip_to_eof(); };
00078         bool skip_relative(S_I x) { flush_write(); clear_read(); return ref->skip_relative(x); };
00079         infinint get_position() { return ref->get_position(); };
00080 
00081     protected:
00082             // inherited from generic_file
00083         S_I inherited_read(char *a, size_t size);
00084         S_I inherited_write(char *a, size_t size);
00085 
00086     private:
00087         struct buf
00088         {
00089             char *buffer;
00090             U_I size; // allocated size
00091             U_I next; // next to read or next place to write to
00092             U_I last; // first to not read in the cache
00093 
00094             buf() { buffer = NULL; size = next = last = 0; };
00095             ~buf() { if(buffer != NULL) delete [] buffer; };
00096         };
00097 
00098         generic_file *ref;
00099 
00100         struct buf buffer_cache;
00101         bool read_mode; // true if in read mode, false if in write mode
00102 
00103         U_I read_obs;
00104         U_I read_unused_rate;
00105         U_I read_overused_rate;
00106 
00107         U_I write_obs;
00108         U_I write_unused_rate;
00109         U_I write_overused_rate;
00110 
00111         U_I stat_read_unused;
00112         U_I stat_read_overused;
00113         U_I stat_read_counter;
00114 
00115         U_I stat_write_overused;
00116         U_I stat_write_counter;
00117 
00118         void flush_write();
00119         void fulfill_read();
00120         void clear_read() { if(read_mode) { buffer_cache.next = buffer_cache.last = 0; } };
00121     };
00122 
00123 } // end of namespace
00124 
00125 #endif
00126 

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