Dart: Makes timing of sending trace events configurable.

mojo/common/dart/lib/src/trace_provider_impl.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:async';
 
 import 'package:mojo/core.dart';
 import 'package:mojo_services/tracing/tracing.mojom.dart';
 
+enum TraceSendTiming {
+  IMMEDIATE,
+  // TODO: Add BATCHED?
+  AT_END,
+}
+
 class TraceProviderImpl implements TraceProvider {
   // Any messages sent before the tracing service connects to us will be
   // recorded and kept until one second after construction of the trace
   // provider. If the tracing service connects before that time, we will replay
   // the recorded trace events.
   //
   // This allows the client to record trace events early during initialization
   // of the app.
   List<String> _message_queue;
   bool _enqueuing;
 
   TraceProviderStub _stub;
   TraceRecorderProxy _recorder;
   // TODO(rudominer) We currently ignore _categories.
   String _categories;
 
-  TraceProviderImpl() {
+  TraceSendTiming _timing;
+
+  TraceProviderImpl([TraceSendTiming timing = TraceSendTiming.IMMEDIATE]) {
     _message_queue = [];
     _enqueuing = true;
-    new Future(() {
-      new Future.delayed(const Duration(seconds: 1), () {
-        if (_enqueuing) {
-          _enqueuing = false;
-          _message_queue.clear();
-        }
-      });
+    _timing = timing;
+    new Future.delayed(const Duration(seconds: 1), () {
+      if (_enqueuing) {
+        _enqueuing = false;
+        _message_queue.clear();
+      }
     });
   }
 
   void connect(MojoMessagePipeEndpoint e) {
     _stub = TraceProviderStub.newFromEndpoint(e);
     _stub.impl = this;
   }
 
   @override
   void startTracing(String categories, TraceRecorderProxy recorder) {
     assert(_recorder == null);
     _recorder = recorder;
     _categories = categories;
     _enqueuing = false;
+    if (_timing == TraceSendTiming.IMMEDIATE) {
+      for (String message in _message_queue) {
+        _recorder.ptr.record(message);
+      }
+      _message_queue.clear();
+    }
   }
 
   @override
   void stopTracing() {
     assert(_recorder != null);
-    for (String message in _message_queue) {
-      _recorder.ptr.record(message);
+    if (_timing == TraceSendTiming.AT_END) {
+      for (String message in _message_queue) {
+        _recorder.ptr.record(message);
+      }
+      _message_queue.clear();
     }
     _recorder.close();
     _recorder = null;
-    _message_queue.clear();
   }
 
   bool isActive() {
     return _enqueuing || _recorder != null;
   }
 
   void sendTraceMessage(String message) {
-    if (isActive()) {
-      _message_queue.add(message);
+    switch (_timing) {
+      case TraceSendTiming.IMMEDIATE:
+        if (_recorder != null) {
+          _recorder.ptr.record(message);
+        } else if (_enqueuing) {
+          _message_queue.add(message);
+        }
+        break;
+      case TraceSendTiming.AT_END:
+        if (isActive()) {
+          _message_queue.add(message);
+        }
+        break;
     }
   }
 }