Is it safe to modify elements of std::valarray<T> concurrently?

Question

If I've understood correctly, since C++11 it has been safe to call const member functions of a container concurrently and modify the elements of a container as long as the container itself is not modified as part of the operation (as seen from e.g. the table concerning thread safety in cppreference.com). Since std::valarray is not listed in the containers section of the (draft) standard, I'm unsure if thread safety also applies to it. In other words,

• Is it safe to read from a std::valarray concurrently (in particular by using operator[] with slices)?
• Is it safe to modify the elements of std::valarray<T> concurrently if the operation on T is safe?

I would like to use std::valarray for a multidimensional array of numbers that would be filled using multiple threads.

Answer 1

If I am reading your question correctly, [res.on.data.races] protects distinct slices from participating in data races, under

A C++ standard library function shall not directly or indirectly access objects accessible by threads other than the current thread unless the objects are accessed directly or indirectly via the function's arguments, including this.

[container.requirements.dataraces] adds extra protection around modifications to distinct elements, which strictly valarray lacks.