src/FileMap.h

   1 /*
   2  * FileMap.h
   3  *
   4  * DEBUG: section 08    Swap File Bitmap
   5  * AUTHOR: Harvest Derived
   6  *
   7  * SQUID Web Proxy Cache          http://www.squid-cache.org/
   8  * ----------------------------------------------------------
   9  *
  10  *  Squid is the result of efforts by numerous individuals from
  11  *  the Internet community; see the CONTRIBUTORS file for full
  12  *  details.   Many organizations have provided support for Squid's
  13  *  development; see the SPONSORS file for full details.  Squid is
  14  *  Copyrighted (C) 2001 by the Regents of the University of
  15  *  California; see the COPYRIGHT file for full details.  Squid
  16  *  incorporates software developed and/or copyrighted by other
  17  *  sources; see the CREDITS file for full details.
  18  *
  19  *  This program is free software; you can redistribute it and/or modify
  20  *  it under the terms of the GNU General Public License as published by
  21  *  the Free Software Foundation; either version 2 of the License, or
  22  *  (at your option) any later version.
  23  *
  24  *  This program is distributed in the hope that it will be useful,
  25  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  26  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  27  *  GNU General Public License for more details.
  28  *
  29  *  You should have received a copy of the GNU General Public License
  30  *  along with this program; if not, write to the Free Software
  31  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
  32  */
  33
  34 #ifndef FILEMAP_H_
  35 #define FILEMAP_H_
  36
  37 #include "typedefs.h"
  38
  39 /** A bitmap used for managing UFS StoreEntry "file numbers".
  40  *
  41  * Nth bit represents whether file number N is used.
  42  * The map automatically grows to hold up to 2^24 bits.
  43  * New bit is "off" or zero by default, representing unused fileno.
  44  * TODO: consider using std::bitset instead.
  45  */
  46 class FileMap
  47 {
  48 public:
  49     FileMap();
  50     ~FileMap();
  51
  52     /** Set the num-th bit in the FileMap
  53      *
  54      * \warning FileMap's backing storage will be extended as needed to
  55      * hold the representation, but  if the bit is already set
  56      * it will break the file number accounting, so the caller must
  57      * ensure that setBit is only called if the bit is not already set,
  58      * by using testBit on it before.
  59      */
  60     bool setBit(sfileno num);
  61
  62     /// Test whether the num-th bit in the FileMap is set
  63     bool testBit(sfileno num) const;
  64
  65     /** Clear the num-th bit in the FileMap
  66      *
  67      * \warning that clearBit doesn't do any bounds checking, nor it
  68      * checks that the bit is set before clearing. The caller will have
  69      * to ensure that both are true using testBit before clearing.
  70      */
  71     void clearBit(sfileno num);
  72
  73     /** locate an unused slot in the FileMap, possibly at or after position suggestion
  74      *
  75      * Obtain the location of an unused slot in the FileMap,
  76      * growing it if needed.
  77      * The suggestion is only an advice; there is no guarantee
  78      * that it will be followed.
  79      */
  80     sfileno allocate(sfileno suggestion);
  81
  82     /// return the max number of slots in the FileMap
  83     int capacity() const {return capacity_;}
  84
  85     /// return the number of used slots in the FileMap
  86     int numFilesInMap() const {return usedSlots_;}
  87 private:
  88     /// grow the FileMap (size is doubled each time, up to 2^24 bits)
  89     void grow();
  90     FileMap(const FileMap &); //no copying
  91     FileMap& operator=(const FileMap &); //no assignments
  92
  93     /// max number of files which can be tracked in the current store
  94     sfileno capacity_;
  95     /// used slots in the map
  96     unsigned int usedSlots_;
  97     /// number of "long ints" making up the filemap
  98     unsigned int nwords;
  99     unsigned long *bitmap;
 100 };
 101
 102 #endif /* FILEMAP_H_ */