[cfe-dev] Attribute parsing at end of translation unit?

[Delesley Hutchins]

But out-of-line declarations are not standard C++, so you wouldn't be
able to compile that code with any other compiler, right?

  -DeLesley

On Tue, Dec 11, 2012 at 2:44 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Mon, Dec 10, 2012 at 3:07 PM, Delesley Hutchins <delesley at google.com> wrote:
>> I am considering changing the way in which thread safety attributes
>> are parsed, but I wanted to get some feedback.
>>
>> Thread safety analysis currently parses attributes at the end of the
>> class where they occur, just like method bodies.  However, this
>> strategy can lead to situations where there is no valid way to
>> annotate a piece of code.  Here's a toy example:
>>
>>
>> class Graph;
>>
>> class Node {
>> public:
>>   // error: Graph has incomplete type.
>>   void reachable(Graph* g, int nodeID) SHARED_LOCKS_REQUIRED(g->mu_);
>>
>> private:
>>   // error: Graph has incomplete type.
>>   std::vector<int> edges_ GUARDED_BY(&Graph::mu_);
>> };
>>
>>
>> class Graph {
>>   friend class Node;
>>
>>   Mutex mu_;
>>   std::vector<Node> nodes_ GUARDED_BY(mu_);
>> };
>>
>>
>> There's a circular dependency here between Graph and Node.  You could
>> try to resolve the dependency by refactoring, but the usual ways of
>> breaking dependencies in C++ don't work with attributes.  The body of
>> a method can be defined outside of its class, but the attribute can't;
>> there's no way to redeclare a method (or a data member) with a new
>> attribute.
>
> We could allow out-of-line declarations for members if they contain
> any thread-safety attributes.



-- 
DeLesley Hutchins | Software Engineer | delesley at google.com | 505-206-0315