Initial backend for metrics in Observatory

sdk/lib/profiler/profiler.dart

Index: sdk/lib/profiler/profiler.dart
diff --git a/sdk/lib/profiler/profiler.dart b/sdk/lib/profiler/profiler.dart
index 0bcae568dfd45b678de3e79710afdcd1fbc74b87..e30fd1dfb2e133ba65803d25df552f725bdce7ab 100644
--- a/sdk/lib/profiler/profiler.dart
+++ b/sdk/lib/profiler/profiler.dart
@@ -4,6 +4,8 @@
 
 library dart.profiler;
 
+import 'dart:convert';
+
 /// 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.
@@ -63,3 +65,135 @@ var _currentTag = _FakeUserTag._defaultTag;
 UserTag getCurrentTag() {
   return _currentTag;
 }
+
+/// Abstract [Metric] class. Metric names must be unique, are hierarchical,
+/// and use periods as separators. For example, 'a.b.c'. Uniqueness is only
+/// enforced when a Metric is registered. The name of a metric cannot contain
+/// the slash ('/') character.
+abstract class Metric {
+  /// [name] of this metric.
+  final String name;
+  /// [description] of this metric.
+  final String description;
+
+  Metric(this.name, this.description) {
+    if (name.contains('/')) {
+      throw new ArgumentError('Invalid Metric name.');
+    }
+  }
+
+  Map _toJSON();
+}
+
+/// A measured value with a min and max. Initial value is min. Value will
+/// be clamped to the interval [min, max].
+class Gauge extends Metric {
+  final double min;
+  final double max;
+
+  double _value;
+  double get value => _value;
+  set value(double v) {
+    if (v < min) {
+      v = min;
+    } else if (v > max) {
+      v = max;
+    }
+    _value = v;
+  }
+
+  Gauge(String name, String description, this.min, this.max)
+      : super(name, description) {
+    if (min is! double) {
+      throw new ArgumentError('min must be a double');
+    }
+    if (max is! double) {
+      throw new ArgumentError('max must be a double');
+    }
+    if (!(min < max)) {
+      throw new ArgumentError('min must be less than max');
+    }
+    _value = min;
+  }
+
+  Map _toJSON() {
+    var map = {
+      'type': 'Gauge',
+      'id': 'metrics/$name',
+      'name': name,
+      'description': description,
+      'value': value,
+      'min': min,
+      'max': max,
+    };
+    return map;
+  }
+}
+
+
+/// A changing value. Initial value is 0.0.
+class Counter extends Metric {
+  Counter(String name, String description)
+      : super(name, description);
+
+  double _value = 0.0;
+  double get value => _value;
+  set value(double v) {
+    _value = v;
+  }
+
+  Map _toJSON() {
+    var map = {
+      'type': 'Counter',
+      'id': 'metrics/$name',
+      'name': name,
+      'description': description,
+      'value': value,
+    };
+    return map;
+  }
+}
+
+class Metrics {
+  static final Map<String, Metric> _metrics = new Map<String, Metric>();
+
+  /// Register [Metric]s to make them visible to Observatory.
+  static void register(Metric metric) {
+    if (metric is! Metric) {
+      throw new ArgumentError('metric must be a Metric');
+    }
+    if (_metrics[metric.name] != null) {
+      throw new ArgumentError('Registered metrics have unique names');
+    }
+    _metrics[metric.name] = metric;
+  }
+
+  /// Deregister [Metric]s to make them not visible to Observatory.
+  static void deregister(Metric metric) {
+    if (metric is! Metric) {
+      throw new ArgumentError('metric must be a Metric');
+    }
+    _metrics.remove(metric.name);
+  }
+
+  static String _printMetric(String id) {
+    var metric = _metrics[id];
+    if (metric == null) {
+      return null;
+    }
+    return JSON.encode(metric._toJSON());
+  }
+
+  static String _printMetrics() {
+    var members = [];
+    for (var metric in _metrics.values) {
+      members.add(metric._toJSON());
+    }
+    var map = {
+      'type': 'MetricList',
+      'id': 'metrics',
+      'members': members,
+    };
+    return JSON.encode(map);
+  }
+}