vmservice: basic object graph serialization.

runtime/bin/vmservice/observatory/lib/object_graph.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library object_graph;
+
+import 'dart:collection';
+import 'dart:typed_data';
+
+// Port of dart::ReadStream from vm/datastream.h.
+class ReadStream {
+  int _cur = 0;
+  ByteData _data;

[Cutch, 2014/12/02 16:46:26]

could this be final?

[koda, 2014/12/02 18:47:12]

Done.

+  
+  ReadStream(this._data);
+  
+  int get pendingBytes => _data.lengthInBytes - _cur;
+  
+  int readUnsigned() {
+    int result = 0;
+    int shift = 0;
+    while (_data.getUint8(_cur) <= maxUnsignedDataPerByte) {
+      result |= _data.getUint8(_cur) << shift;
+      shift += dataBitsPerByte;
+      ++_cur;
+    }
+    result |= (_data.getUint8(_cur) & byteMask) << shift;
+    ++_cur;
+    return result;
+  }
+
+  static const int dataBitsPerByte = 7;
+  static const int byteMask = (1 << dataBitsPerByte) - 1;
+  static const int maxUnsignedDataPerByte = byteMask;
+}
+
+class ObjectVertex {
+  int _id;

[Cutch, 2014/12/02 16:46:26]

could this be final?

[koda, 2014/12/02 18:47:12]

Done.

+  int size;
+  int classId;

[Cutch, 2014/12/02 16:46:26]

could these be made final? or at least have non-public setters.

[koda, 2014/12/02 18:47:12]

Hid the setters.

+  List<ObjectVertex> succ = new List<ObjectVertex>();

[Cutch, 2014/12/02 16:46:26]

could this be final?

[koda, 2014/12/02 18:47:12]

Done.

+  ObjectVertex(this._id);
+}
+
+// See implementation of ObjectGraph::Serialize for format.
+class ObjectGraph {
+  Map<int, ObjectVertex> _idToVertex = new Map<int, ObjectVertex>();

[Cutch, 2014/12/02 16:46:26]

could this be final?

[koda, 2014/12/02 18:47:12]

Done.

+
+  ObjectVertex _asVertex(int id) {
+    return _idToVertex.putIfAbsent(id, () => new ObjectVertex(id));
+  }
+
+  void _addFrom(ReadStream stream) {
+    ObjectVertex obj = _asVertex(stream.readUnsigned());
+    obj.size = stream.readUnsigned();
+    obj.classId = stream.readUnsigned();

[Cutch, 2014/12/02 16:46:26]

if you read the id, size, and classId and then called _asVertex(id, size,
classId) you could make all the fields final in ObjectVertex

[koda, 2014/12/02 18:47:12]

No.

+    int last = stream.readUnsigned();
+    while (last != 0) {
+      obj.succ.add(_asVertex(last));

[Cutch, 2014/12/02 16:46:26]

Oh, I see why you can't make _asVertex take all three properties.

[koda, 2014/12/02 18:47:12]

Right. I added a comment explaining the two-stage initialization.

+      last = stream.readUnsigned();
+    }
+  }
+
+  ObjectGraph(ReadStream reader) {
+    while (reader.pendingBytes > 0) {
+      _addFrom(reader);
+    }
+  }
+
+  Iterable<ObjectVertex> get vertices => _idToVertex.values;
+}