Initial UserTag and dart:profiler library

sdk/lib/profiler/profiler.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 dart.profiler;
+
+/// A UserTag can be used to group samples in the Observatory profiler.
+abstract class UserTag {
+  /// The maximum number of UserTag instances that can be created by a program.
+  static const MAX_USER_TAGS = 64;
+
+  factory UserTag(String label) => new _FakeUserTag(label);
+
+  /// Label of [this].
+  String get label;
+
+  /// Make [this] the current tag for the isolate.
+  makeCurrent();
+}
+
+// This is a fake implementation of UserTag so that code can compile and run
+// in dart2js.
+class _FakeUserTag implements UserTag {
+  static List _instances = [];
+
+  _FakeUserTag.real(this.label);
+
+  factory _FakeUserTag(String label) {
+    // Canonicalize by name.
+    for (var tag in _instances) {
+      if (tag.label == label) {
+        return tag;
+      }
+    }
+    // Throw an exception if we've reached the maximum number of user tags.
+    if (_instances.length == UserTag.MAX_USER_TAGS) {
+      throw new UnsupportedError(
+          'UserTag instance limit (${UserTag.MAX_USER_TAGS}) reached.');
+    }
+    // Create a new instance and add it to the instance list.
+    var instance = new _FakeUserTag.real(label);
+    _instances.add(instance);
+    return instance;
+  }
+
+  final String label;
+
+  makeCurrent() {
+    _currentTag = this;
+  }
+}
+
+var _currentTag = null;
+
+/// Returns the current [UserTag] for the isolate.
+UserTag getCurrentTag() {
+  return _currentTag;
+}
+
+/// Sets the current [UserTag] for the isolate to null. Returns current tag
+/// before clearing.
+UserTag clearCurrentTag() {
+  var old = _currentTag;
+  _currentTag = null;
+  return old;
+}