[ dart:developer ] Added optional parent parameter to TimelineTask constructors.

Specifying a parent will result in an argument being added to 'start'
events for that TimelineTask named 'parentId', which contains the task
ID of the parent. This is to be used by DevTools to show relationships
between asynchronous tasks that are not currently supported in the trace
event format used by Catapult.

Change-Id: Id0a030f018f5a6ac1e3b0ef2e89c1cd732790f02
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/119520
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Kenzie Schmoll <kenzieschmoll@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>

CHANGELOG.md

@@ -23,6 +23,11 @@ main() { foo(() {}); }
 * Default values of parameters of abstract methods are no longer available
   via `dart:mirrors`.
 
+#### `dart:developer`
+
+* Added optional `parent` paremeter to `TimelineTask` constructors to allow for
+  linking of asynchronous timeline events in the DevTools timeline view.
+
 ### Dart VM
 
 ### Tools

runtime/observatory/tests/service/get_vm_timeline_rpc_test.dart

@@ -13,7 +13,8 @@ primeTimeline() {
   Timeline.startSync('apple');
   Timeline.instantSync('ISYNC', arguments: {'fruit': 'banana'});
   Timeline.finishSync();
-  TimelineTask task = new TimelineTask();
+  TimelineTask parentTask = TimelineTask.withTaskId(42);
+  TimelineTask task = TimelineTask(parent: parentTask);
   task.start('TASK1', arguments: {'task1-start-key': 'task1-start-value'});
   task.instant('ITASK',
       arguments: {'task1-instant-key': 'task1-instant-value'});
@@ -126,8 +127,8 @@ var tests = <VMTest>[
         eventsContains(dartEvents, 'i', 'ISYNC', {'fruit': 'banana'}), isTrue);
     expect(eventsContains(dartEvents, 'X', 'apple'), isTrue);
     expect(
-        eventsContains(
-            dartEvents, 'b', 'TASK1', {'task1-start-key': 'task1-start-value'}),
+        eventsContains(dartEvents, 'b', 'TASK1',
+            {'task1-start-key': 'task1-start-value', 'parentId': 42}),
         isTrue);
     expect(
         eventsContains(dartEvents, 'e', 'TASK1',

sdk/lib/developer/timeline.dart

@@ -180,11 +180,23 @@ class Timeline {
 /// [TimelineTask] in the other isolate.
 class TimelineTask {
   /// Create a task. The task ID will be set by the system.
-  TimelineTask() : _taskId = _getNextAsyncId() {}
+  ///
+  /// If [parent] is provided, the parent's task ID is provided as argument
+  /// 'parentId' when [start] is called. In DevTools, this argument will result
+  /// in this [TimelineTask] being linked to the [parent] [TimelineTask].
+  TimelineTask({TimelineTask parent})
+      : _parent = parent,
+        _taskId = _getNextAsyncId() {}
 
   /// Create a task with an explicit [taskId]. This is useful if you are
   /// passing a task from one isolate to another.
-  TimelineTask.withTaskId(int taskId) : _taskId = taskId {
+  ///
+  /// If [parent] is provided, the parent's task ID is provided as argument
+  /// 'parentId' when [start] is called. In DevTools, this argument will result
+  /// in this [TimelineTask] being linked to the [parent] [TimelineTask].
+  TimelineTask.withTaskId(int taskId, {TimelineTask parent})
+      : _parent = parent,
+        _taskId = taskId {
     ArgumentError.checkNotNull(taskId, 'taskId');
   }
 
@@ -195,7 +207,10 @@ class TimelineTask {
     ArgumentError.checkNotNull(name, 'name');
     var block = new _AsyncBlock._(name, _taskId);
     _stack.add(block);
-    block._start(arguments);
+    block._start({
+      if (arguments != null) ...arguments,
+      if (_parent != null) 'parentId': _parent._taskId,
+    });
   }
 
   /// Emit an instant event for this task.
@@ -237,6 +252,7 @@ class TimelineTask {
     return r;
   }
 
+  final TimelineTask _parent;
   final int _taskId;
   final List<_AsyncBlock> _stack = [];
 }

sdk_nnbd/lib/developer/timeline.dart

@@ -182,11 +182,23 @@ class Timeline {
 /// [TimelineTask] in the other isolate.
 class TimelineTask {
   /// Create a task. The task ID will be set by the system.
-  TimelineTask() : _taskId = _getNextAsyncId() {}
+  ///
+  /// If [parent] is provided, the parent's task ID is provided as argument
+  /// 'parentId' when [start] is called. In DevTools, this argument will result
+  /// in this [TimelineTask] being linked to the [parent] [TimelineTask].
+  TimelineTask({TimelineTask parent})
+      : _parent = parent,
+        _taskId = _getNextAsyncId() {}
 
   /// Create a task with an explicit [taskId]. This is useful if you are
   /// passing a task from one isolate to another.
-  TimelineTask.withTaskId(int taskId) : _taskId = taskId {
+  ///
+  /// If [parent] is provided, the parent's task ID is provided as argument
+  /// 'parentId' when [start] is called. In DevTools, this argument will result
+  /// in this [TimelineTask] being linked to the [parent] [TimelineTask].
+  TimelineTask.withTaskId(int taskId, {TimelineTask parent})
+      : _parent = parent,
+        _taskId = taskId {
     ArgumentError.checkNotNull(taskId, 'taskId');
   }
 
@@ -197,7 +209,10 @@ class TimelineTask {
     ArgumentError.checkNotNull(name, 'name');
     var block = new _AsyncBlock._(name, _taskId);
     _stack.add(block);
-    block._start(arguments);
+    block._start({
+      if (arguments != null) ...arguments,
+      if (_parent != null) 'parentId': _parent._taskId,
+    });
   }
 
   /// Emit an instant event for this task.
@@ -239,6 +254,7 @@ class TimelineTask {
     return r;
   }
 
+  final TimelineTask _parent;
   final int _taskId;
   final List<_AsyncBlock> _stack = [];
 }