Why do I get future_error with async? - c++11

Question

I need to start execution of vector of tasks in parallel and wait until finished. Here is how I did this, but I get future_error on MSVC. Small utility to split vector into parts:
template<typename T>
vector<vector<T>> split(const vector<T>& vec, size_t n) {
vector<vector<T>> outVec;
size_t length = vec.size() / n;
size_t remain = vec.size() % n;
size_t begin = 0;
size_t end = 0;
for (size_t i = 0; i < std::min(n, vec.size()); ++i) {
end += (remain > 0) ? (length + !!(remain--)) : length;
outVec.push_back(std::vector<T>(vec.begin() + begin, vec.begin() + end));
begin = end;
}
return outVec;
};
launch async execution:
template <typename T, typename R, typename F>
void execInParallel(vector<T> &tasks, vector<R> &res, F&&f, int cores) {
function<int(int &t)> fn(std::forward<F>(f));
auto parts = split(tasks, cores);
vector<future<vector<R>>*> threads;
for (auto part: parts) {
future<vector<R>> thrd=async(launch::async, [&](vector<T> tasks) {
vector<R> rs;
for (auto&t : tasks) {
rs.push_back(fn(t));
}
return rs;
}, part);
threads.push_back(&thrd);
}
for (auto&thrd : threads) {
vector<R> rs = thrd->get();
for (auto &r : rs)
res.push_back(r);
}
};
test on stupid example:
int main(){
vector<int> tasks,res;
tasks.push_back(1);
tasks.push_back(7);
tasks.push_back(19);
execInParallel(tasks,res, [&](int&t) {
return t+8;
}, 2);
return 0;
}
May be I am inventing a bicycle? Is there anything like that in C++11 or boost out of the box? Any example available?