std::valarray and parallelization

May be it is so stupid question.

On this site I read that

The valarray specification allows for libraries to implement it with several efficiency optimizations, such as parallelization of certain operations

What is at the moment with parallelization of std::valarray on different platforms and compilers? GCC, VS2010/2013, clang?

Especially with standard threading support from C++11.

UPD: And if some sompilers don't support this feature. What is the best way to do this: apply some function to elements of a container in several threads? Obviously, naive solution would be short and works well with std::thread but maybe exist better solution?