Exemplo n.º 1
0
		private void UseScratch ()
		{
			if (scratch == null)
				scratch = new BetterBitArray (searcher.MaxDoc ());
			else
				scratch.SetAll (false);
			collector.Array = scratch;
		}
Exemplo n.º 2
0
		public BetterBitArray (BetterBitArray bits)
		{
			if (bits == null)
				throw new ArgumentNullException ("bits");

			_length = bits._length;
			_array = new int [(_length + 31) / 32];

			Array.Copy(bits._array, _array, _array.Length);
		}
Exemplo n.º 3
0
 void checkOperand(BetterBitArray operand)
 {
     if (operand == null)
     {
         throw new ArgumentNullException();
     }
     if (operand._length != _length)
     {
         throw new ArgumentException();
     }
 }
Exemplo n.º 4
0
        public BetterBitArray(BetterBitArray bits)
        {
            if (bits == null)
            {
                throw new ArgumentNullException("bits");
            }

            _length = bits._length;
            _array  = new int [(_length + 31) / 32];

            Array.Copy(bits._array, _array, _array.Length);
        }
Exemplo n.º 5
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        static void Main()
        {
            Random rng = new Random();

            for (int trial = 0; trial < 10000; ++trial)
            {
                bool failed = false;

                BetterBitArray ba = new BetterBitArray(rng.Next(100000) + 1);

                Hashtable true_hash = new Hashtable();
                int       N         = 1 + rng.Next(10000);
                for (int k = 0; k < N; ++k)
                {
                    int j = rng.Next(ba.Count);
                    ba [j]        = true;
                    true_hash [j] = true;
                }

                int i = 0;
                while (i < ba.Count)
                {
                    i = ba.GetNextTrueIndex(i);
                    if (i < ba.Count)
                    {
                        if (true_hash.Contains(i))
                        {
                            true_hash.Remove(i);
                        }
                        else
                        {
                            Console.WriteLine("Spurious true at {0}", i);
                            failed = true;
                        }
                    }

                    ++i;
                }

                if (true_hash.Count > 0)
                {
                    Console.WriteLine("Missed some trues:");
                    foreach (int k in true_hash.Values)
                    {
                        Console.WriteLine("  {0}", k);
                    }
                    failed = true;
                }

                Console.WriteLine("Trial #{0}: {1}", trial + 1,
                                  failed ? "FAILED" : "ok");
            }
        }
Exemplo n.º 6
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		public SmallIntArray (int length, int max_int)
		{
			this.length = length;
			this.max_int = max_int;

			this.bits_per_int = 0;
			while (max_int != 0) {
				++bits_per_int;
				max_int = max_int >> 1;
			}

			this.bit_array = new BetterBitArray (this.length * this.bits_per_int);
		}
Exemplo n.º 7
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        public SmallIntArray(int length, int max_int)
        {
            this.length  = length;
            this.max_int = max_int;

            this.bits_per_int = 0;
            while (max_int != 0)
            {
                ++bits_per_int;
                max_int = max_int >> 1;
            }

            this.bit_array = new BetterBitArray(this.length * this.bits_per_int);
        }
Exemplo n.º 8
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        public BetterBitArray Xor(BetterBitArray value)
        {
            checkOperand(value);

            int ints = (_length + 31) / 32;

            for (int i = 0; i < ints; i++)
            {
                _array [i] ^= value._array [i];
            }

            _version++;
            _contains_true     = ContainsTrueState.Maybe; // better
            _cached_true_count = -1;                      // better
            return(this);
        }
Exemplo n.º 9
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        public void Incr(BetterBitArray bit_array)
        {
            if (bit_array.Length != length)
            {
                throw new Exception("Incr BetterBitArray has wrong length!");
            }

            int i = 0;

            while (i < length)
            {
                i = bit_array.GetNextTrueIndex(i);
                if (i >= length)
                {
                    break;
                }
                Set(i, Get(i) + 1);
                ++i;
            }
        }
Exemplo n.º 10
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        public BetterBitArray Or(BetterBitArray value)
        {
            checkOperand(value);

            int ints = (_length + 31) / 32;

            for (int i = 0; i < ints; i++)
            {
                _array [i] |= value._array [i];
            }

            _version++;
            if (_contains_true == ContainsTrueState.Yes ||
                value._contains_true == ContainsTrueState.Yes)
            {
                _contains_true = ContainsTrueState.Yes;
            }
            else
            {
                _contains_true = ContainsTrueState.Maybe; // better
            }
            _cached_true_count = -1;                      // better
            return(this);
        }
Exemplo n.º 11
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		// There are two ways we can determine the max_results
		// most recent items:  
		//
		// One is to instantiate Lucene documents for each of
		// the document IDs in primary_matches.  This is a
		// fairly expensive operation.
		//
		// The other is to walk through the list of all
		// document IDs in descending time order.  This is
		// a less expensive operation, but adds up over time
		// on large data sets.
		//
		// We can walk about 2.5 docs for every Document we
		// instantiate.  So what we'll do, if we have more
		// matches than available hits, is walk (m * 1.25)
		// docs to see if we can fill out the top 100 hits.
		// If not, we'll fall back to creating documents
		// for all of them.

		private static ArrayList ScanRecentDocs (IndexReader	    primary_reader,
						    IndexReader		    secondary_reader,
						    BetterBitArray	    primary_matches,
						    Dictionary<int, Hit>    hits_by_id,
						    int			    max_results,
						    ref int		    total_number_of_matches,
						    HitFilter		    hit_filter,
						    string		    index_name)
		{
			Stopwatch a = new Stopwatch ();
			a.Start ();

			TermDocs docs = primary_reader.TermDocs ();
			TermEnum enumerator = primary_reader.Terms (new Term ("InvertedTimestamp", String.Empty));
			ArrayList results = new ArrayList (max_results);
			int docs_found = 0;
			int docs_walked = 0;
			int hit_filter_removed = 0;
			int max_docs = (int) (primary_matches.TrueCount * 1.25);

			Term term;
			TermDocs secondary_term_docs = null;
			if (secondary_reader != null)
				secondary_term_docs = secondary_reader.TermDocs ();

			do {
				term = enumerator.Term ();
			
				if (term.Field () != "InvertedTimestamp")
					break;

				docs.Seek (enumerator);

				while (docs.Next ()
				       && docs_found < max_results
				       && docs_walked < max_docs) {
					int doc_id = docs.Doc ();

					if (primary_matches.Get (doc_id)) {
						Document doc = primary_reader.Document (doc_id);
						Hit hit = CreateHit (doc, secondary_reader, secondary_term_docs);

						// If we have a HitFilter, apply it.
						if (hit_filter != null && ! hit_filter (hit)) {
							if (Debug)
								Log.Debug ("Filtered out {0}", hit.Uri);
							hit_filter_removed ++;
							continue;
						}
						hits_by_id [doc_id] = hit;
						// Add the result, last modified first
						results.Add (hit);
						docs_found++;
					}
			
					docs_walked++;
				}
			} while (enumerator.Next ()
				 && docs_found < max_results
				 && docs_walked < max_docs);

			docs.Close ();
			if (secondary_term_docs != null)
				secondary_term_docs.Close ();

			// If we've found all the docs we can return in a subset!
			// Fantastic, we've probably short circuited a slow search.
			if (docs_found != max_results) {
				// Otherwise bad luck! Not all docs found
				// Start afresh - this time traversing all results
				results = null;
			} else {
				// Adjust total_number_of_matches. We need to do this to avoid scenarios like the following:
				// max_hits = 100. Matched 100 results. But hit filter removed 30. So 70 results will be returned.
				// We want to avoid saying "Showing top 70 of 100". Note that since we are not passing
				// every document in the index through the hit_filter, when we say "Showing top 100 of 1234", the
				// 1234 could actually be much less. But since max_hits was 100, that will not mislead the user.
				total_number_of_matches -= hit_filter_removed;
			}

			a.Stop ();
			if (Debug) {
				Log.Debug (">>> {0}: Walked {1} items, populated an enum with {2} items in {3}", index_name, docs_walked, docs_found, a);
				
				if (docs_found == max_results)
					Log.Debug (">>> {0}: Successfully short circuited timestamp ordering!", index_name);
			}

			return results;
		}
Exemplo n.º 12
0
 public BetterBitArrayEnumerator(BetterBitArray ba)
 {
     _index    = -1;
     _bitArray = ba;
     _version  = ba._version;
 }
Exemplo n.º 13
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			public BetterBitArrayEnumerator (BetterBitArray ba)
			{
				_index = -1;
				_bitArray = ba;
				_version = ba._version;
			}
Exemplo n.º 14
0
		static void Main ()
		{
			Random rng = new Random ();
			
			for (int trial = 0; trial < 10000; ++trial) {

				bool failed = false;
				
				BetterBitArray ba = new BetterBitArray (rng.Next (100000) + 1);
				
				Hashtable true_hash = new Hashtable ();
				int N = 1 + rng.Next (10000);
				for (int k = 0; k < N; ++k) {
					int j = rng.Next (ba.Count);
					ba [j] = true;
					true_hash [j] = true;
				}

				int i = 0;
				while (i < ba.Count) {
					i = ba.GetNextTrueIndex (i);
					if (i < ba.Count) {
						if (true_hash.Contains (i)) {
							true_hash.Remove (i);
						} else {
							Console.WriteLine ("Spurious true at {0}", i);
							failed = true;
						}
					}
					
					++i;
				}

				if (true_hash.Count > 0) {
					Console.WriteLine ("Missed some trues:");
					foreach (int k in true_hash.Values)
						Console.WriteLine ("  {0}", k);
					failed = true;
				}

				Console.WriteLine ("Trial #{0}: {1}", trial+1,
						   failed ? "FAILED" : "ok");
			}
		}
Exemplo n.º 15
0
		public void Incr (BetterBitArray bit_array)
		{
			if (bit_array.Length != length)
				throw new Exception ("Incr BetterBitArray has wrong length!");

			int i = 0;
			while (i < length) {
				i = bit_array.GetNextTrueIndex (i);
				if (i >= length)
					break;
				Set (i, Get (i) + 1);
				++i;
			}
		}
Exemplo n.º 16
0
		public LuceneBitArray (LNS.IndexSearcher searcher) : base (searcher.MaxDoc ())
		{
			this.searcher = searcher;
			this.collector = new BitArrayHitCollector ();
			this.scratch = null;
		}
Exemplo n.º 17
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		public BetterBitArray Xor (BetterBitArray value)
		{
			checkOperand (value);

			int ints = (_length + 31) / 32;
			for (int i = 0; i < ints; i++)
				_array [i] ^= value._array [i];

			_version++;
			_contains_true = ContainsTrueState.Maybe; // better
			_cached_true_count = -1; // better
			return this;
		}
Exemplo n.º 18
0
 public BitArrayHitCollector (BetterBitArray matches)
 {
         this.matches = matches;
 }
Exemplo n.º 19
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		private static void GenerateQueryResults (IndexReader       primary_reader,
							  IndexReader       secondary_reader,
							  BetterBitArray    primary_matches,
							  IQueryResult      result,
							  ICollection       query_term_list,
							  int               max_results,
							  HitFilter         hit_filter,
							  string            index_name)
		{
			int num_hits;

			if (Debug)
				Logger.Log.Debug (">>> {0}: Initially handed {1} matches", index_name, primary_matches.TrueCount);

			if (primary_matches.TrueCount <= max_results) {
				if (Debug)
					Logger.Log.Debug (">>> {0}: Initial count is within our limit of {1}", index_name, max_results);
				num_hits = primary_matches.TrueCount;
			} else {
				if (Debug)
					Logger.Log.Debug (">>> {0}: Number of hits is capped at {1}", index_name, max_results);
				num_hits = max_results;
			}

			Stopwatch total, d, e;
			total = new Stopwatch ();
			d = new Stopwatch ();
			e = new Stopwatch ();

			total.Start ();

			ArrayList final_list_of_hits = null;

			// This is used only for scoring
			Dictionary<int, Hit> hits_by_id = new Dictionary<int, Hit> (num_hits);

			int total_number_of_matches = primary_matches.TrueCount;

			if (primary_matches.TrueCount > max_results)
				final_list_of_hits = ScanRecentDocs (primary_reader,
					secondary_reader,
					primary_matches,
					hits_by_id,
					max_results,
					ref total_number_of_matches,
					hit_filter,
					index_name);

			if (final_list_of_hits == null)
				final_list_of_hits = FindRecentResults (primary_reader,
					secondary_reader,
					primary_matches,
					hits_by_id,
					max_results,
					ref total_number_of_matches,
					hit_filter,
					index_name);

			d.Start ();

			ScoreHits (hits_by_id, primary_reader, query_term_list);
			hits_by_id = null;

			d.Stop ();

			if (Debug)
				Log.Debug (">>> {0}: Scored hits in {1}", index_name, d);

			e.Start ();

			// 25 hits seems to be the sweet spot: anything lower
			// and serialization overhead gets us, higher takes
			// longer to send out.
			const int MAX_QUEUED_HITS = 25;
			int sent_index = 0;

			// Break up the hits into reasonably sized chunks for
			// sending over the wire.
			for (int i = 0; i < final_list_of_hits.Count; ++i) {
				// Flush our hits
				if (i > 0 && i % MAX_QUEUED_HITS == 0) {
					result.Add (final_list_of_hits.GetRange (0, MAX_QUEUED_HITS));
					final_list_of_hits.RemoveRange (0, MAX_QUEUED_HITS);
					i -= MAX_QUEUED_HITS;
				}
			}

			// Flush the remaining hits
			result.Add (final_list_of_hits, total_number_of_matches);
			final_list_of_hits = null;

			e.Stop ();

			if (Debug)
				Log.Debug (">>> {0}: Hit filters executed and results sent in {1}", index_name, e);

			total.Stop ();

			if (Debug) {
				Logger.Log.Debug (">>> {0}: GenerateQueryResults time statistics:", index_name);
				//Logger.Log.Debug (">>> {0}:   Short circuit {1,6} ({2:0.0}%)", index_name, a == null ? "N/A" : a.ToString (), a == null ? 0.0 : 100 * a.ElapsedTime / total.ElapsedTime);
				//Logger.Log.Debug (">>> {0}:     Create docs {1,6} ({2:0.0}%)", index_name, b, 100 * b.ElapsedTime / total.ElapsedTime);
				//Logger.Log.Debug (">>> {0}:    Hit assembly {1,6} ({2:0.0}%)", index_name, c, 100 * c.ElapsedTime / total.ElapsedTime);
				Logger.Log.Debug (">>> {0}:     Scored hits {1,6} ({2:0.0}%)", index_name, d, 100 * d.ElapsedTime / total.ElapsedTime);
				Logger.Log.Debug (">>> {0}:    Results sent {1,6} ({2:0.0}%)", index_name, e, 100 * e.ElapsedTime / total.ElapsedTime);
				Logger.Log.Debug (">>> {0}:           TOTAL {1,6}", index_name, total);
			}
		}
Exemplo n.º 20
0
		// Any whitelists that are passed in must be fully joined, or
		// query results will be incorrect.
		private static BetterBitArray DoRequiredQueries_TwoIndex (LNS.IndexSearcher primary_searcher,
									  LNS.IndexSearcher secondary_searcher,
									  ArrayList primary_queries,
									  ArrayList secondary_queries,
									  BetterBitArray primary_whitelist,
									  BetterBitArray secondary_whitelist)
		{
			ArrayList match_info_list;
			match_info_list = new ArrayList ();

			// First, do all of the low-level queries
			// and store them in our MatchInfo 
			for (int i = 0; i < primary_queries.Count; ++i) {
				LNS.Query pq, sq;
				pq = primary_queries [i] as LNS.Query;
				sq = secondary_queries [i] as LNS.Query;

				LuceneBitArray p_matches = null, s_matches = null;
				p_matches = new LuceneBitArray (primary_searcher);
				if (pq != null) {
					p_matches.Or (pq);
					if (primary_whitelist != null)
						p_matches.And (primary_whitelist);
				}

				s_matches = new LuceneBitArray (secondary_searcher);
				if (sq != null) {
					s_matches.Or (sq);
					if (secondary_whitelist != null)
						s_matches.And (secondary_whitelist);
				}

				MatchInfo info;
				info = new MatchInfo ();
				info.PrimaryMatches = p_matches;
				info.SecondaryMatches = s_matches;
				info.RestrictBy (null); // a hack to initialize the UpperBound
				match_info_list.Add (info);
			}

			// We want to be smart about the order we do this in,
			// to minimize the expense of the Join.
			while (match_info_list.Count > 1) {

				// linear scan to find the minimum
				int index_min = 0;
				for (int i = 1; i < match_info_list.Count; ++i)
					if (((MatchInfo) match_info_list [i]).CompareTo ((MatchInfo) match_info_list [index_min]) < 0)
						index_min = i;

				MatchInfo smallest;
				smallest = match_info_list [index_min] as MatchInfo;
				match_info_list.RemoveAt (index_min);

				// We can short-circuit if our smallest set of
				// matches is empty.
				if (smallest.UpperBound == 0)
					return smallest.PrimaryMatches; // this must be an empty array.

				smallest.Join ();

				foreach (MatchInfo info in match_info_list)
					info.RestrictBy (smallest);
			}
			
			// For the final pair, we don't need to do a full join:
			// mapping the secondary onto the primary is sufficient
			MatchInfo last;
			last = match_info_list [0] as MatchInfo;
			last.SecondaryMatches.ProjectOnto (last.PrimaryMatches);

			return last.PrimaryMatches;
		}		
Exemplo n.º 21
0
		////////////////////////////////////////////////////////////////

		//
		// Special logic for handling our set of required queries
		//

		// This is the easy case: we just combine all of the queries
		// into one big BooleanQuery.
		private static BetterBitArray DoRequiredQueries (LNS.IndexSearcher primary_searcher,
								 ArrayList primary_queries,
								 BetterBitArray primary_whitelist)
		{
			LNS.BooleanQuery combined_query;
			combined_query = new LNS.BooleanQuery ();
			foreach (LNS.Query query in primary_queries)
				combined_query.Add (query, LNS.BooleanClause.Occur.MUST);

			LuceneBitArray matches;
			matches = new LuceneBitArray (primary_searcher, combined_query);
			if (primary_whitelist != null)
				matches.And (primary_whitelist);

			return matches;
		}
Exemplo n.º 22
0
		private static ArrayList   FindRecentResults (IndexReader	    primary_reader,
							      IndexReader	    secondary_reader,
							      BetterBitArray	    primary_matches,
							      Dictionary<int, Hit>  hits_by_id,
							      int		    max_results,
							      ref int		    total_number_of_matches,
							      HitFilter		    hit_filter,
							      string		    index_name)
		{
			Stopwatch b = new Stopwatch ();
			b.Start ();
			
			int count = 0;
			Document doc;

			ArrayList all_docs = null;
			TopScores top_docs = null;
			TermDocs term_docs = null;

			if (primary_matches.TrueCount > max_results)
				top_docs = new TopScores (max_results);
			else
				all_docs = new ArrayList (primary_matches.TrueCount);

			if (secondary_reader != null)
				term_docs = secondary_reader.TermDocs ();

			for (int match_index = primary_matches.Count; ; match_index --) {
				// Walk across the matches backwards, since newer
				// documents are more likely to be at the end of
				// the index.
				match_index = primary_matches.GetPreviousTrueIndex (match_index);
				if (match_index < 0)
					break;

				count++;

				doc = primary_reader.Document (match_index, fields_timestamp_uri);

				// Check the timestamp --- if we have already reached our
				// limit, we might be able to reject it immediately.
				string timestamp_str;
				long timestamp_num = 0;

				timestamp_str = doc.Get ("Timestamp");
				if (timestamp_str == null) {
					Logger.Log.Warn ("No timestamp on {0}!", GetUriFromDocument (doc));
				} else {
					timestamp_num = Int64.Parse (doc.Get ("Timestamp"));
					if (top_docs != null && ! top_docs.WillAccept (timestamp_num))
						continue;
				}

				// Get the actual hit now
				// doc was created with only 2 fields, so first get the complete lucene document for primary document.
				// Also run our hit_filter now, if we have one. Since we insist of returning max_results
				// most recent hits, any hits that would be filtered out should happen now and not later.
				Hit hit = CreateHit (primary_reader.Document (match_index), secondary_reader, term_docs);
				if (hit_filter != null && ! hit_filter (hit)) {
					if (Debug)
						Log.Debug ("Filtered out {0}", hit.Uri);
					total_number_of_matches --;
					continue;
				}

				hits_by_id [match_index] = hit;

				// Add the document to the appropriate data structure.
				// We use the timestamp_num as the score, so high
				// scores correspond to more-recent timestamps.
				if (all_docs != null)
					all_docs.Add (hit);
				else
					top_docs.Add (timestamp_num, hit);
			}

			if (term_docs != null)
				term_docs.Close ();

			b.Stop ();

			if (Debug)
				Log.Debug (">>> {0}: Instantiated and scanned {1} documents in {2}", index_name, count, b);

			if (all_docs != null) {
				// Sort results before sending
				all_docs.Sort ();
				return all_docs;
			} else {
				return top_docs.TopScoringObjects;
			}
		}
Exemplo n.º 23
0
		// Return all directories with name
		public ICollection GetAllDirectoryNameInfo (string name)
		{
			// First we assemble a query to find all of the directories.
			string field_name;
			field_name = PropertyToFieldName (PropertyType.Keyword,
							  Property.IsDirectoryPropKey);
			LNS.Query isdir_query = new LNS.TermQuery (new Term (field_name, "true"));

			LNS.Query query = null;

			if (name == null) {
				query = isdir_query;
			} else {
				string dirname_field;
				dirname_field = PropertyToFieldName (PropertyType.Text,
								     Property.TextFilenamePropKey);
				LNS.Query dirname_query;
				dirname_query = LuceneCommon.StringToQuery (dirname_field, name, null);
				LNS.BooleanQuery bool_query = new LNS.BooleanQuery ();
				bool_query.Add (isdir_query, LNS.BooleanClause.Occur.MUST);
				bool_query.Add (dirname_query, LNS.BooleanClause.Occur.MUST);

				query = bool_query;
			}

			// Then we actually run the query
			LNS.IndexSearcher searcher;
			//searcher = new LNS.IndexSearcher (SecondaryStore);
			searcher = LuceneCommon.GetSearcher (SecondaryStore);

			BetterBitArray matches;
			matches = new BetterBitArray (searcher.MaxDoc ());

			BitArrayHitCollector collector;
			collector = new BitArrayHitCollector (matches);

			searcher.Search (query, null, collector);
			
			// Finally we pull all of the matching documents,
			// convert them to NameInfo, and store them in a list.

			ArrayList match_list = new ArrayList ();
			int i = 0;
			while (i < matches.Count) {
				
				i = matches.GetNextTrueIndex (i);
				if (i >= matches.Count)
					break;

				Document doc;
				doc = searcher.Doc (i, fields_nameinfo);

				NameInfo info;
				info = DocumentToNameInfo (doc);

				match_list.Add (info);

				++i;
			}

			LuceneCommon.ReleaseSearcher (searcher);

			return match_list;
		}
Exemplo n.º 24
0
                // Returns a list of all files and directories in dir
                static ICollection GetAllItemsInDirectory (DirectoryInfo dir)
                {
                        // form the query
                        string parent_uri_str = PathToUri (dir.FullName).ToString ();

                        // Instead of taking the painfull way of using BeagrepAnalyzer, lets just add the prefix manually
                        // LuceneCommon thinks exposing secret property type encoding is bad, I think so too... except for now
                        string key = "prop:k:" + Property.ParentDirUriPropKey;
                        //Logger.Log.Debug ("Querying for {0}={1}", parent_uri_str, key);
                        LNS.Query query = new LNS.TermQuery (new Term (key, parent_uri_str));

                        // do the search
                        LNS.IndexSearcher searcher;
                        searcher = LuceneCommon.GetSearcher (driver.PrimaryStore);

                        BetterBitArray matches;
                        matches = new BetterBitArray (searcher.MaxDoc ());

                        BitArrayHitCollector collector;
                        collector = new BitArrayHitCollector (matches);

                        searcher.Search (query, null, collector);

                        // Finally we pull all of the matching documents,
                        // convert them to Dirent, and store them in a list.

                        ArrayList match_list = new ArrayList ();
                        int i = 0;
                        while (i < matches.Count) {

                                i = matches.GetNextTrueIndex (i);
                                if (i >= matches.Count)
                                        break;

                                Document doc;
                                doc = searcher.Doc (i);

                                Dirent info;
                                info = DocumentToDirent (doc);

                                match_list.Add (info);

                                ++i;
                        }

                        LuceneCommon.ReleaseSearcher (searcher);
                        //Logger.Log.Debug ("Found {0} items in {1}", match_list.Count, dir.FullName);

                        return match_list;
                }
Exemplo n.º 25
0
		void checkOperand (BetterBitArray operand)
		{
			if (operand == null)
				throw new ArgumentNullException ();
			if (operand._length != _length)
				throw new ArgumentException ();
		}