Reuse IndexedScore instances, as emptying the values is faster than discarding and re-allocating memory. (#8297)

Author: isoos

app/lib/search/mem_index.dart

@@ -27,6 +27,7 @@ class InMemoryPackageIndex {
   late final TokenIndex<String> _descrIndex;
   late final TokenIndex<String> _readmeIndex;
   late final TokenIndex<IndexedApiDocPage> _apiSymbolIndex;
+  late final _scorePool = ScorePool(_packageNameIndex._packageNames);
 
   /// Adjusted score takes the overall score and transforms
   /// it linearly into the [0.4-1.0] range.
@@ -116,8 +117,16 @@ class InMemoryPackageIndex {
   }
 
   PackageSearchResult search(ServiceSearchQuery query) {
-    final packageScores = IndexedScore(_packageNameIndex._packageNames, 1.0);
+    return _scorePool.withScore(
+      value: 1.0,
+      fn: (score) {
+        return _search(query, score);
+      },
+    );
+  }
 
+  PackageSearchResult _search(
+      ServiceSearchQuery query, IndexedScore<String> packageScores) {
     // filter on package prefix
     if (query.parsedQuery.packagePrefix != null) {
       final String prefix = query.parsedQuery.packagePrefix!.toLowerCase();
@@ -308,11 +317,17 @@ class InMemoryPackageIndex {
           nameMatches.add(word);
         }
 
-        final wordScore =
-            _packageNameIndex.searchWord(word, filterOnNonZeros: packageScores);
-        _descrIndex.searchAndAccumulate(word, score: wordScore);
-        _readmeIndex.searchAndAccumulate(word, weight: 0.75, score: wordScore);
-        packageScores.multiplyAllFrom(wordScore);
+        _scorePool.withScore(
+          value: 0.0,
+          fn: (wordScore) {
+            _packageNameIndex.searchWord(word,
+                score: wordScore, filterOnNonZeros: packageScores);
+            _descrIndex.searchAndAccumulate(word, score: wordScore);
+            _readmeIndex.searchAndAccumulate(word,
+                weight: 0.75, score: wordScore);
+            packageScores.multiplyAllFrom(wordScore);
+          },
+        );
       }
 
       final topApiPages =
@@ -483,7 +498,8 @@ class PackageNameIndex {
   Map<String, double> search(String text) {
     IndexedScore<String>? score;
     for (final w in splitForQuery(text)) {
-      final s = searchWord(w, filterOnNonZeros: score);
+      final s = IndexedScore(_packageNames);
+      searchWord(w, score: s, filterOnNonZeros: score);
       if (score == null) {
         score = s;
       } else {
@@ -498,11 +514,12 @@ class PackageNameIndex {
   ///
   /// When [filterOnNonZeros] is present, only the indexes with an already
   /// non-zero value are evaluated.
-  IndexedScore<String> searchWord(
+  void searchWord(
     String word, {
+    required IndexedScore<String> score,
     IndexedScore<String>? filterOnNonZeros,
   }) {
-    final score = IndexedScore(_packageNames);
+    assert(score.keys.length == _packageNames.length);
     final singularWord = word.length <= 3 || !word.endsWith('s')
         ? word
         : word.substring(0, word.length - 1);
@@ -543,7 +560,6 @@ class PackageNameIndex {
         }
       }
     }
-    return score;
   }
 }
 

app/lib/search/token_index.dart

@@ -100,6 +100,7 @@ class TokenIndex<K> {
   /// scoring.
   IndexedScore<K> searchWords(List<String> words, {double weight = 1.0}) {
     IndexedScore<K>? score;
+
     weight = math.pow(weight, 1 / words.length).toDouble();
     for (final w in words) {
       final s = IndexedScore(_ids);
@@ -142,6 +143,30 @@ extension StringTokenIndexExt on TokenIndex<String> {
   }
 }
 
+/// A reusable pool for [IndexedScore] instances to spare some memory allocation.
+class ScorePool<K> {
+  final List<K> _keys;
+  final _pool = <IndexedScore<K>>[];
+
+  ScorePool(this._keys);
+
+  R withScore<R>({
+    required double value,
+    required R Function(IndexedScore<K> score) fn,
+  }) {
+    late IndexedScore<K> score;
+    if (_pool.isNotEmpty) {
+      score = _pool.removeLast();
+      score._values.setAll(0, Iterable.generate(score.length, (_) => value));
+    } else {
+      score = IndexedScore<K>(_keys, value);
+    }
+    final r = fn(score);
+    _pool.add(score);
+    return r;
+  }
+}
+
 /// Mutable score list that can accessed via integer index.
 class IndexedScore<K> {
   final List<K> _keys;