Implement bitarray pool in package search index. (#8797)

Author: isoos

app/lib/search/mem_index.dart

@@ -29,6 +29,7 @@ class InMemoryPackageIndex {
   late final TokenIndex<String> _descrIndex;
   late final TokenIndex<String> _readmeIndex;
   late final TokenIndex<IndexedApiDocPage> _apiSymbolIndex;
+  late final _bitArrayPool = BitArrayPool(_documents.length);
   late final _scorePool = ScorePool(_packageNameIndex._packageNames);
 
   /// Maps the tag strings to a list of document index values using bit arrays.
@@ -140,22 +141,21 @@ class InMemoryPackageIndex {
     if ((query.offset ?? 0) >= _documents.length) {
       return PackageSearchResult.empty();
     }
-    return _scorePool.withScore(
-      value: 0.0,
-      fn: (score) {
-        return _search(query, score);
-      },
-    );
+    return _bitArrayPool.withBitArrayAllSet(fn: (array) {
+      return _scorePool.withScore(
+        value: 0.0,
+        fn: (score) {
+          return _search(query, array, score);
+        },
+      );
+    });
   }
 
   PackageSearchResult _search(
     ServiceSearchQuery query,
+    BitArray packages,
     IndexedScore<String> packageScores,
   ) {
-    // TODO: implement pooling of this object similarly to [ScorePool].
-    final packages = BitArray(_documents.length)
-      ..setRange(0, _documents.length);
-
     // filter on tags
     final combinedTagsPredicate =
         query.tagsPredicate.appendPredicate(query.parsedQuery.tagsPredicate);

app/lib/search/token_index.dart

@@ -5,6 +5,7 @@
 import 'dart:math' as math;
 
 import 'package:meta/meta.dart';
+import 'package:pub_dev/third_party/bit_array/bit_array.dart';
 
 import 'text_utils.dart';
 
@@ -183,6 +184,33 @@ class ScorePool<K> {
   }
 }
 
+/// A reusable pool for [BitArray] instances to spare some memory allocation.
+class BitArrayPool<K> {
+  final int _length;
+  final _pool = <BitArray>[];
+
+  BitArrayPool(this._length);
+
+  BitArray _acquireAllSet() {
+    final array = _pool.isNotEmpty ? _pool.removeLast() : BitArray(_length);
+    array.setRange(0, _length);
+    return array;
+  }
+
+  void _release(BitArray array) {
+    _pool.add(array);
+  }
+
+  R withBitArrayAllSet<R>({
+    required R Function(BitArray array) fn,
+  }) {
+    final array = _acquireAllSet();
+    final r = fn(array);
+    _release(array);
+    return r;
+  }
+}
+
 /// Mutable score list that can accessed via integer index.
 class IndexedScore<K> {
   final List<K> _keys;