Dart - make vTable fixed size (expect the number of fields when creating) (#6735)

6 files changed, 65 insertions, 51 deletions

diff --git a/dart/example/monster_my_game.sample_generated.dart b/dart/example/monster_my_game.sample_generated.dart
index eae52b61..57c3d6b3 100644
--- a/dart/example/monster_my_game.sample_generated.dart
+++ b/dart/example/monster_my_game.sample_generated.dart
@@ -220,7 +220,7 @@ class MonsterBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(10);
   }
 
   int addPos(int offset) {
@@ -315,7 +315,7 @@ class MonsterObjectBuilder extends fb.ObjectBuilder {
     final int? equippedOffset = _equipped?.getOrCreateOffset(fbBuilder);
     final int? pathOffset = _path == null ? null
         : fbBuilder.writeListOfStructs(_path!);
-    fbBuilder.startTable();
+    fbBuilder.startTable(10);
     if (_pos != null) {
       fbBuilder.addStruct(0, _pos!.finish(fbBuilder));
     }
@@ -375,7 +375,7 @@ class WeaponBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(2);
   }
 
   int addNameOffset(int? offset) {
@@ -407,7 +407,7 @@ class WeaponObjectBuilder extends fb.ObjectBuilder {
   @override
   int finish(fb.Builder fbBuilder) {
     final int? nameOffset = fbBuilder.writeString(_name);
-    fbBuilder.startTable();
+    fbBuilder.startTable(2);
     fbBuilder.addOffset(0, nameOffset);
     fbBuilder.addInt16(1, _damage);
     return fbBuilder.endTable();
diff --git a/dart/lib/flat_buffers.dart b/dart/lib/flat_buffers.dart
index ca635feb..55b825a0 100644
--- a/dart/lib/flat_buffers.dart
+++ b/dart/lib/flat_buffers.dart
@@ -472,12 +472,12 @@ class Builder {
     }
   }
 
-  /// Start a new table.  Must be finished with [endTable] invocation.
-  void startTable() {
+  /// Start a new table. Must be finished with [endTable] invocation.
+  void startTable(int numFields) {
     if (_currentVTable != null) {
       throw new StateError('Inline tables are not supported.');
     }
-    _currentVTable = new _VTable();
+    _currentVTable = new _VTable(numFields);
     _currentTableEndTail = _tail;
   }
 
@@ -1229,8 +1229,14 @@ class _FbBoolList extends _FbList<bool> {
 class _VTable {
   static const int _metadataLength = 4;
 
-  final fieldTails = <int?>[];
-  final fieldOffsets = <int>[];
+  final int numFields;
+
+  // Note: fieldOffsets start as "tail offsets" and are then transformed by
+  // [computeFieldOffsets()] to actual offsets when a table is finished.
+  final Uint32List fieldOffsets;
+  bool offsetsComputed = false;
+
+  _VTable(this.numFields) : fieldOffsets = Uint32List(numFields);
 
   /// The size of the table that uses this VTable.
   int tableSize = 0;
@@ -1241,17 +1247,20 @@ class _VTable {
 
   int get _vTableSize => numOfUint16 * _sizeofUint16;
 
-  int get numOfUint16 => 1 + 1 + fieldTails.length;
+  int get numOfUint16 => 1 + 1 + numFields;
 
+  @pragma('vm:prefer-inline')
   void addField(int field, int offset) {
-    while (fieldTails.length <= field) {
-      fieldTails.add(null);
-    }
-    fieldTails[field] = offset;
+    assert(!offsetsComputed);
+    assert(offset > 0); // it's impossible for field to start at the buffer end
+    assert(offset <= 4294967295); // uint32 max
+    fieldOffsets[field] = offset;
   }
 
+  @pragma('vm:prefer-inline')
   bool _offsetsMatch(int vt2Start, ByteData buf) {
-    for (int i = 0; i < fieldOffsets.length; i++) {
+    assert(offsetsComputed);
+    for (int i = 0; i < numFields; i++) {
       if (fieldOffsets[i] !=
           buf.getUint16(vt2Start + _metadataLength + (2 * i), Endian.little)) {
         return false;
@@ -1261,17 +1270,22 @@ class _VTable {
   }
 
   /// Fill the [fieldOffsets] field.
+  @pragma('vm:prefer-inline')
   void computeFieldOffsets(int tableTail) {
-    assert(fieldOffsets.isEmpty);
-    for (int? fieldTail in fieldTails) {
-      int fieldOffset = fieldTail == null ? 0 : tableTail - fieldTail;
-      fieldOffsets.add(fieldOffset);
+    assert(!offsetsComputed);
+    offsetsComputed = true;
+    for (var i = 0; i < numFields; i++) {
+      if (fieldOffsets[i] != 0) {
+        fieldOffsets[i] = tableTail - fieldOffsets[i];
+      }
     }
   }
 
   /// Outputs this VTable to [buf], which is is expected to be aligned to 16-bit
   /// and have at least [numOfUint16] 16-bit words available.
+  @pragma('vm:prefer-inline')
   void output(ByteData buf, int bufOffset) {
+    assert(offsetsComputed);
     // VTable size.
     buf.setUint16(bufOffset, numOfUint16 * 2, Endian.little);
     bufOffset += 2;
@@ -1279,8 +1293,8 @@ class _VTable {
     buf.setUint16(bufOffset, tableSize, Endian.little);
     bufOffset += 2;
     // Field offsets.
-    for (int fieldOffset in fieldOffsets) {
-      buf.setUint16(bufOffset, fieldOffset, Endian.little);
+    for (int i = 0; i < numFields; i++) {
+      buf.setUint16(bufOffset, fieldOffsets[i], Endian.little);
       bufOffset += 2;
     }
   }
diff --git a/dart/test/flat_buffers_test.dart b/dart/test/flat_buffers_test.dart
index 6df4b306..783f9fc0 100644
--- a/dart/test/flat_buffers_test.dart
+++ b/dart/test/flat_buffers_test.dart
@@ -224,15 +224,15 @@ class BuilderTest {
 
   void test_error_startTable_duringTable() {
     Builder builder = new Builder();
-    builder.startTable();
+    builder.startTable(0);
     expect(() {
-      builder.startTable();
+      builder.startTable(0);
     }, throwsStateError);
   }
 
   void test_error_writeString_duringTable() {
     Builder builder = new Builder();
-    builder.startTable();
+    builder.startTable(1);
     expect(() {
       builder.writeString('12345');
     }, throwsStateError);
@@ -242,7 +242,7 @@ class BuilderTest {
     Uint8List byteList;
     {
       Builder builder = new Builder(initialSize: 0);
-      builder.startTable();
+      builder.startTable(0);
       int offset = builder.endTable();
       builder.finish(offset, 'Az~ÿ');
       byteList = builder.buffer;
@@ -298,7 +298,7 @@ class BuilderTest {
     List<int> byteList;
     {
       final builder = Builder(initialSize: 0, allocator: CustomAllocator());
-      builder.startTable();
+      builder.startTable(2);
       builder.addInt32(0, 10, 10);
       builder.addInt32(1, 20, 10);
       int offset = builder.endTable();
@@ -325,7 +325,7 @@ class BuilderTest {
     Uint8List byteList;
     {
       builder ??= new Builder(initialSize: 0);
-      builder.startTable();
+      builder.startTable(3);
       builder.addInt32(0, 10);
       builder.addInt32(1, 20);
       builder.addInt32(2, 30);
@@ -362,7 +362,7 @@ class BuilderTest {
       Builder builder = new Builder(initialSize: 0);
       int? latinStringOffset = builder.writeString(latinString);
       int? unicodeStringOffset = builder.writeString(unicodeString);
-      builder.startTable();
+      builder.startTable(2);
       builder.addOffset(0, latinStringOffset);
       builder.addOffset(1, unicodeStringOffset);
       int offset = builder.endTable();
@@ -387,7 +387,7 @@ class BuilderTest {
     {
       builder ??= new Builder(initialSize: 0);
       int? stringOffset = builder.writeString('12345');
-      builder.startTable();
+      builder.startTable(7);
       builder.addBool(0, true);
       builder.addInt8(1, 10);
       builder.addInt32(2, 20);
@@ -554,7 +554,7 @@ class BuilderTest {
       // write the object #1
       int object1;
       {
-        builder.startTable();
+        builder.startTable(2);
         builder.addInt32(0, 10);
         builder.addInt32(1, 20);
         object1 = builder.endTable();
@@ -562,7 +562,7 @@ class BuilderTest {
       // write the object #1
       int object2;
       {
-        builder.startTable();
+        builder.startTable(2);
         builder.addInt32(0, 100);
         builder.addInt32(1, 200);
         object2 = builder.endTable();
@@ -608,7 +608,7 @@ class BuilderTest {
       builder ??= new Builder(initialSize: 0);
       int listOffset = builder.writeList(
           [builder.writeString('12345')!, builder.writeString('ABC')!]);
-      builder.startTable();
+      builder.startTable(1);
       builder.addOffset(0, listOffset);
       int offset = builder.endTable();
       builder.finish(offset);
diff --git a/dart/test/monster_test_my_game.example2_generated.dart b/dart/test/monster_test_my_game.example2_generated.dart
index 82c3f4ba..723572c5 100644
--- a/dart/test/monster_test_my_game.example2_generated.dart
+++ b/dart/test/monster_test_my_game.example2_generated.dart
@@ -37,7 +37,7 @@ class Monster {
 
 class MonsterT {
   int pack(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(0);
     return fbBuilder.endTable();
   }
 
@@ -62,7 +62,7 @@ class MonsterObjectBuilder extends fb.ObjectBuilder {
   /// Finish building, and store into the [fbBuilder].
   @override
   int finish(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(0);
     return fbBuilder.endTable();
   }
 
diff --git a/dart/test/monster_test_my_game.example_generated.dart b/dart/test/monster_test_my_game.example_generated.dart
index 5d11bb71..8e0fc0b4 100644
--- a/dart/test/monster_test_my_game.example_generated.dart
+++ b/dart/test/monster_test_my_game.example_generated.dart
@@ -387,7 +387,7 @@ class TestSimpleTableWithEnumT {
       this.color = Color.Green});
 
   int pack(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(1);
     fbBuilder.addUint8(0, color.value);
     return fbBuilder.endTable();
   }
@@ -412,7 +412,7 @@ class TestSimpleTableWithEnumBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(1);
   }
 
   int addColor(Color? color) {
@@ -436,7 +436,7 @@ class TestSimpleTableWithEnumObjectBuilder extends fb.ObjectBuilder {
   /// Finish building, and store into the [fbBuilder].
   @override
   int finish(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(1);
     fbBuilder.addUint8(0, _color?.value);
     return fbBuilder.endTable();
   }
@@ -847,7 +847,7 @@ class StatT {
 
   int pack(fb.Builder fbBuilder) {
     final int? idOffset = fbBuilder.writeString(id);
-    fbBuilder.startTable();
+    fbBuilder.startTable(3);
     fbBuilder.addOffset(0, idOffset);
     fbBuilder.addInt64(1, val);
     fbBuilder.addUint16(2, count);
@@ -874,7 +874,7 @@ class StatBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(3);
   }
 
   int addIdOffset(int? offset) {
@@ -913,7 +913,7 @@ class StatObjectBuilder extends fb.ObjectBuilder {
   @override
   int finish(fb.Builder fbBuilder) {
     final int? idOffset = fbBuilder.writeString(_id);
-    fbBuilder.startTable();
+    fbBuilder.startTable(3);
     fbBuilder.addOffset(0, idOffset);
     fbBuilder.addInt64(1, _val);
     fbBuilder.addUint16(2, _count);
@@ -964,7 +964,7 @@ class ReferrableT {
       this.id = 0});
 
   int pack(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(1);
     fbBuilder.addUint64(0, id);
     return fbBuilder.endTable();
   }
@@ -989,7 +989,7 @@ class ReferrableBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(1);
   }
 
   int addId(int? id) {
@@ -1013,7 +1013,7 @@ class ReferrableObjectBuilder extends fb.ObjectBuilder {
   /// Finish building, and store into the [fbBuilder].
   @override
   int finish(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(1);
     fbBuilder.addUint64(0, _id);
     return fbBuilder.endTable();
   }
@@ -1341,7 +1341,7 @@ class MonsterT {
         : fbBuilder.writeListUint8(testrequirednestedflatbuffer!);
     final int? scalarKeySortedTablesOffset = scalarKeySortedTables == null ? null
         : fbBuilder.writeList(scalarKeySortedTables!.map((b) => b.pack(fbBuilder)).toList());
-    fbBuilder.startTable();
+    fbBuilder.startTable(50);
     if (pos != null) {
       fbBuilder.addStruct(0, pos!.pack(fbBuilder));
     }
@@ -1417,7 +1417,7 @@ class MonsterBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(50);
   }
 
   int addPos(int offset) {
@@ -1831,7 +1831,7 @@ class MonsterObjectBuilder extends fb.ObjectBuilder {
         : fbBuilder.writeListUint8(_testrequirednestedflatbuffer!);
     final int? scalarKeySortedTablesOffset = _scalarKeySortedTables == null ? null
         : fbBuilder.writeList(_scalarKeySortedTables!.map((b) => b.getOrCreateOffset(fbBuilder)).toList());
-    fbBuilder.startTable();
+    fbBuilder.startTable(50);
     if (_pos != null) {
       fbBuilder.addStruct(0, _pos!.finish(fbBuilder));
     }
@@ -1979,7 +1979,7 @@ class TypeAliasesT {
         : fbBuilder.writeListInt8(v8!);
     final int? vf64Offset = vf64 == null ? null
         : fbBuilder.writeListFloat64(vf64!);
-    fbBuilder.startTable();
+    fbBuilder.startTable(12);
     fbBuilder.addInt8(0, i8);
     fbBuilder.addUint8(1, u8);
     fbBuilder.addInt16(2, i16);
@@ -2015,7 +2015,7 @@ class TypeAliasesBuilder {
   final fb.Builder fbBuilder;
 
   void begin() {
-    fbBuilder.startTable();
+    fbBuilder.startTable(12);
   }
 
   int addI8(int? i8) {
@@ -2120,7 +2120,7 @@ class TypeAliasesObjectBuilder extends fb.ObjectBuilder {
         : fbBuilder.writeListInt8(_v8!);
     final int? vf64Offset = _vf64 == null ? null
         : fbBuilder.writeListFloat64(_vf64!);
-    fbBuilder.startTable();
+    fbBuilder.startTable(12);
     fbBuilder.addInt8(0, _i8);
     fbBuilder.addUint8(1, _u8);
     fbBuilder.addInt16(2, _i16);
diff --git a/dart/test/monster_test_my_game_generated.dart b/dart/test/monster_test_my_game_generated.dart
index 7f0fcda5..07618f6c 100644
--- a/dart/test/monster_test_my_game_generated.dart
+++ b/dart/test/monster_test_my_game_generated.dart
@@ -37,7 +37,7 @@ class InParentNamespace {
 
 class InParentNamespaceT {
   int pack(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(0);
     return fbBuilder.endTable();
   }
 
@@ -62,7 +62,7 @@ class InParentNamespaceObjectBuilder extends fb.ObjectBuilder {
   /// Finish building, and store into the [fbBuilder].
   @override
   int finish(fb.Builder fbBuilder) {
-    fbBuilder.startTable();
+    fbBuilder.startTable(0);
     return fbBuilder.endTable();
   }