[observatory] Fix race in getCpuProfileTimeline.

This function would iterate vm.isolates twice with an async gap in between and expect no isolates to start or exit in the mean time.

Change-Id: I1a79dd9494a4d0431b112db61c0660ce2df00cca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136560
Reviewed-by: Ben Konyi <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

runtime/observatory/lib/src/repositories/timeline_base.dart

@@ -14,11 +14,11 @@ class TimelineRepositoryBase {
   static const kTimeOriginMicros = 'timeOriginMicros';
   static const kTimeExtentMicros = 'timeExtentMicros';
 
-  Future<void> _formatSamples(
-      M.Isolate isolate, Map traceObject, S.ServiceMap cpuSamples) async {
+  Future<void> _formatSamples(M.Isolate isolate, Map traceObject,
+      Future<S.ServiceObject> cpuSamples) async {
     const kRootFrameId = 0;
     final profile = SampleProfile();
-    await profile.load(isolate as S.ServiceObjectOwner, cpuSamples);
+    await profile.load(isolate as S.ServiceObjectOwner, await cpuSamples);
     final trie = profile.loadFunctionTree(M.ProfileTreeDirection.inclusive);
     final root = trie.root;
     int nextId = kRootFrameId;
@@ -66,24 +66,20 @@ class TimelineRepositoryBase {
   Future<Map> getCpuProfileTimeline(M.VMRef ref,
       {int timeOriginMicros, int timeExtentMicros}) async {
     final S.VM vm = ref as S.VM;
-    final sampleRequests = <Future>[];
+    final traceObject = <String, dynamic>{
+      _kStackFrames: {},
+      _kTraceEvents: [],
+    };
 
-    for (final isolate in vm.isolates) {
-      sampleRequests.add(vm.invokeRpc('getCpuSamples', {
+    await Future.wait(vm.isolates.map((isolate) {
+      final samples = vm.invokeRpc('getCpuSamples', {
         'isolateId': isolate.id,
         if (timeOriginMicros != null) kTimeOriginMicros: timeOriginMicros,
         if (timeExtentMicros != null) kTimeExtentMicros: timeExtentMicros,
-      }));
-    }
+      });
+      return _formatSamples(isolate, traceObject, samples);
+    }));
 
-    final completed = await Future.wait(sampleRequests);
-    final traceObject = <String, dynamic>{
-      _kStackFrames: {},
-      _kTraceEvents: [],
-    };
-    for (int i = 0; i < vm.isolates.length; ++i) {
-      await _formatSamples(vm.isolates[i], traceObject, completed[i]);
-    }
     return traceObject;
   }
 

runtime/observatory/tests/service/get_zone_memory_info_rpc_test.dart

@@ -12,7 +12,7 @@ var tests = <VMTest>[
     isInstanceOf<int> isInt = new isInstanceOf<int>();
     // Just iterate over all the isolates to confirm they have
     // the correct fields needed to examine zone memory usage.
-    for (Isolate isolate in vm.isolates) {
+    for (Isolate isolate in new List.from(vm.isolates)) {
       await isolate.reload();
       expect(isolate.zoneHighWatermark, isInt);
       expect(isolate.threads, isNotNull);