Braddock Gaskill wrote:
it isn't ok.
boost/function/function_template.hpp lines 653-659
template<typename Functor> void assign_to(Functor f) { static vtable_type stored_vtable(f); if (stored_vtable.assign_to(f, functor)) vtable = &stored_vtable; else vtable = 0; }
function static is not thread safe
You've just succeeded in scaring the hell out of me. Just how unsafe is boost::function?
As far as I can see, the situation here is less problematic than with the general thread-safety problem of function-local statics. This one is local to a template member function and the object initialization is identical for concurrent calls (addresses of two static functions which only depend on the template arguments), so you cannot end up with a corrupted stored_vtable. There is however a potential race condition regarding the internal "this local static variable is initialized" state. I think with >=2 processors running that same code, one may see that flag set with the actual object not being properly initialized from its point of view (due to write reordering by the other processor). Given the relative "distance" between this initialization code and a possible access of either manager or invoker member in the vtable, I think the problem is of a rather academical nature. But the code is still not strictly correct from my understanding. The theoretical outcome is undefined behaviour for the first copy operation or invocation of each function object with a given distinct signature and assigned functor type. Regards Timmo Stange