src/FileMap.h

   1 /*
   2  * Copyright (C) 1996-2020 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 /* DEBUG: section 08    Swap File Bitmap */
  10
  11 #ifndef FILEMAP_H_
  12 #define FILEMAP_H_
  13
  14 #include "store/forward.h"
  15
  16 /** A bitmap used for managing UFS StoreEntry "file numbers".
  17  *
  18  * Nth bit represents whether file number N is used.
  19  * The map automatically grows to hold up to 2^24 bits.
  20  * New bit is "off" or zero by default, representing unused fileno.
  21  * TODO: consider using std::bitset instead.
  22  */
  23 class FileMap
  24 {
  25 public:
  26     FileMap();
  27     ~FileMap();
  28
  29     /** Set the num-th bit in the FileMap
  30      *
  31      * \warning FileMap's backing storage will be extended as needed to
  32      * hold the representation, but  if the bit is already set
  33      * it will break the file number accounting, so the caller must
  34      * ensure that setBit is only called if the bit is not already set,
  35      * by using testBit on it before.
  36      */
  37     bool setBit(sfileno num);
  38
  39     /// Test whether the num-th bit in the FileMap is set
  40     bool testBit(sfileno num) const;
  41
  42     /** Clear the num-th bit in the FileMap
  43      *
  44      * \warning that clearBit doesn't do any bounds checking, nor it
  45      * checks that the bit is set before clearing. The caller will have
  46      * to ensure that both are true using testBit before clearing.
  47      */
  48     void clearBit(sfileno num);
  49
  50     /** locate an unused slot in the FileMap, possibly at or after position suggestion
  51      *
  52      * Obtain the location of an unused slot in the FileMap,
  53      * growing it if needed.
  54      * The suggestion is only an advice; there is no guarantee
  55      * that it will be followed.
  56      */
  57     sfileno allocate(sfileno suggestion);
  58
  59     /// return the max number of slots in the FileMap
  60     int capacity() const {return capacity_;}
  61
  62     /// return the number of used slots in the FileMap
  63     int numFilesInMap() const {return usedSlots_;}
  64 private:
  65     /// grow the FileMap (size is doubled each time, up to 2^24 bits)
  66     void grow();
  67     FileMap(const FileMap &); //no copying
  68     FileMap& operator=(const FileMap &); //no assignments
  69
  70     /// max number of files which can be tracked in the current store
  71     sfileno capacity_;
  72     /// used slots in the map
  73     unsigned int usedSlots_;
  74     /// number of "long ints" making up the filemap
  75     unsigned int nwords;
  76     unsigned long *bitmap;
  77 };
  78
  79 #endif /* FILEMAP_H_ */
  80