- Clarify the order of setting the interrupt bit and posting a message in

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 47a410f7630531cf08574c11142cf5dfaf1f8ab1..eb12fb5df1ebcaaccaf1a00a922f6c68c92f79b1 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1601,7 +1601,13 @@ DART_EXPORT void Dart_InterruptIsolate(Dart_Isolate isolate) {
   }
   // TODO(16615): Validate isolate parameter.
   Isolate* iso = reinterpret_cast<Isolate*>(isolate);
+  // Schedule the interrupt. The isolate will notice this bit being set if it
+  // is currently executing in Dart code.
   iso->ScheduleInterrupts(Isolate::kApiInterrupt);
+  // If the isolate is blocked on the message queue, we post a dummy message
+  // to the isolate's main port. The message will be ultimately ignored, but as
+  // part of handling the message the interrupt bit which was set above will be
+  // honored.
   // Can't use Dart_Post() since there isn't a current isolate.
   Dart_CObject api_null = { Dart_CObject_kNull , { 0 } };
   Dart_PostCObject(iso->main_port(), &api_null);