xapian-core/backends/multi/multi_valuelist.h

   1 /** @file
   2  * @brief Class for merging ValueList objects from subdatabases.
   3  */
   4 /* Copyright (C) 2007,2008,2009,2017 Olly Betts
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  19  */
  20
  21 #ifndef XAPIAN_INCLUDED_MULTI_VALUELIST_H
  22 #define XAPIAN_INCLUDED_MULTI_VALUELIST_H
  23
  24 #include "backends/valuelist.h"
  25
  26 #include "backends/databaseinternal.h"
  27 #include "backends/multi.h"
  28
  29 #include <string>
  30
  31 struct SubValueList {
  32     ValueList * valuelist;
  33     unsigned shard;
  34
  35     SubValueList(ValueList * vl, unsigned shard_)
  36         : valuelist(vl), shard(shard_) { }
  37
  38     ~SubValueList() {
  39         delete valuelist;
  40     }
  41
  42     void skip_to(Xapian::docid did, Xapian::doccount n_shards) {
  43         // Calculate the docid in this shard which is the same or later than
  44         // did (which may be in a different shard).
  45         Xapian::docid shard_did = shard_docid(did, n_shards);
  46         if (shard_number(did, n_shards) > shard)
  47             ++shard_did;
  48         valuelist->skip_to(shard_did);
  49     }
  50
  51     Xapian::docid get_docid() const {
  52         return valuelist->get_docid();
  53     }
  54
  55     Xapian::docid get_merged_docid(unsigned n_shards) const {
  56         return unshard(valuelist->get_docid(), shard, n_shards);
  57     }
  58
  59     std::string get_value() const { return valuelist->get_value(); }
  60
  61     void next() {
  62         valuelist->next();
  63     }
  64
  65     bool at_end() const { return valuelist->at_end(); }
  66 };
  67
  68 /// Class for merging ValueList objects from subdatabases.
  69 class MultiValueList : public ValueList {
  70     /// Don't allow assignment.
  71     void operator=(const MultiValueList &);
  72
  73     /// Don't allow copying.
  74     MultiValueList(const MultiValueList &);
  75
  76     /// Current docid (or 0 if we haven't started yet).
  77     Xapian::docid current_docid = 0;
  78
  79     /// Number of SubValueList* entries in valuelists.
  80     Xapian::doccount count;
  81
  82     /// Array of sub-valuelists which we use as a heap.
  83     SubValueList** valuelists;
  84
  85     /// The value slot we're iterating over.
  86     Xapian::valueno slot;
  87
  88     Xapian::doccount n_shards;
  89
  90   public:
  91     /// Constructor.
  92     MultiValueList(Xapian::doccount n_shards_,
  93                    SubValueList** valuelists_,
  94                    Xapian::valueno slot_)
  95         : count(n_shards_),
  96           valuelists(valuelists_),
  97           slot(slot_),
  98           n_shards(n_shards_)
  99     {
 100     }
 101
 102     /// Destructor.
 103     ~MultiValueList();
 104
 105     /// Return the docid at the current position.
 106     Xapian::docid get_docid() const;
 107
 108     /// Return the value at the current position.
 109     std::string get_value() const;
 110
 111     /// Return the value slot for the current position/this iterator.
 112     Xapian::valueno get_valueno() const;
 113
 114     /// Return true if the current position is past the last entry in this list.
 115     bool at_end() const;
 116
 117     /** Advance the current position to the next document in the value stream.
 118      *
 119      *  The list starts before the first entry in the list, so next(),
 120      *  skip_to() or check() must be called before any methods which need the
 121      *  context of the current position.
 122      */
 123     void next();
 124
 125     /** Skip forward to the specified docid.
 126      *
 127      *  If the specified docid isn't in the list, position ourselves on the
 128      *  first document after it (or at_end() if no greater docids are present).
 129      */
 130     void skip_to(Xapian::docid);
 131
 132     /** Check if the specified docid occurs in this valuestream.
 133      *
 134      *  The caller is required to ensure that the specified @a docid actually
 135      *  exists in the database.
 136      *
 137      *  This method acts like skip_to() if that can be done at little extra
 138      *  cost, in which case it then sets @a valid to true.
 139      *
 140      *  Otherwise it simply checks if a particular docid is present.  If it
 141      *  is, it returns true.  If it isn't, it returns false, and leaves the
 142      *  position unspecified (and hence the result of calling methods which
 143      *  depend on the current position, such as get_docid(), are also
 144      *  unspecified).  In this state, next() will advance to the first matching
 145      *  position after @a docid, and skip_to() will act as it would if the
 146      *  position was the first matching position after @a docid.
 147      *
 148      *  The default implementation calls skip_to().
 149      */
 150     bool check(Xapian::docid did);
 151
 152     /// Return a string description of this object.
 153     std::string get_description() const;
 154 };
 155
 156 #endif // XAPIAN_INCLUDED_MULTIVALUELIST_H