Track loading happening in parallel with background compilation and abort compilation if necessary.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index 5220506471715723ec77beaa3932f6ef96c02b58..fb74a733ff7aa0c8464ce562200f9ef8f7e210af 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -491,6 +491,24 @@ void Parser::SetPosition(TokenPosition position) {
 }
 
 
+// Set state and increments generational count so that thge background compiler
+// can detect if loading/top-level-parsing occured during compilation.
+class TopLevelParsingScope : public ValueObject {
+ public:
+  explicit TopLevelParsingScope(Isolate* isolate) : isolate_(isolate) {
+    isolate_->set_top_level_parsing(true);
+    isolate_->IncrLoadingInvalidationGen();
+  }
+  ~TopLevelParsingScope() {
+    isolate_->set_top_level_parsing(false);
+    isolate_->IncrLoadingInvalidationGen();
+  }

[siva, 2016/03/28 17:20:14]

Both constructor and destructor are incrementing the loading_invalidation_gen_
value, is that needed? Do you want to differentiate between start of top level
parsing and end?

[srdjan, 2016/03/28 19:54:54]

I do not need to differentiate. The only information I need is that the a
loading occurred. In that context, I only need to increment the loading counter
at the exit, since the start and loading is covered by the IsTopLevelParsing
state/check. 

+
+ private:
+  Isolate* isolate_;
+};
+
+
 void Parser::ParseCompilationUnit(const Library& library,
                                   const Script& script) {
   Thread* thread = Thread::Current();
@@ -507,6 +525,7 @@ void Parser::ParseCompilationUnit(const Library& library,
   }
 #endif
 
+  TopLevelParsingScope scope(thread->isolate());
   Parser parser(script, library, TokenPosition::kMinSource);
   parser.ParseTopLevel();
 }