Re: Passing std::unique_ptr to std::thread's target

SG <>
Fri, 12 Aug 2011 16:39:12 CST
On 12 Aug., 00:02, Andy Venikov wrote:

On 08/10/2011 09:04 PM, Daniel Kr?gler wrote:

Exactly. glibc++ is using bind internally to forward the arguments to the
thread functor.
So, it looks like bind can't be used internally by thread library to
pass arguments.

Right. The easiest solution is probably to make use of make_tuple:

  auto argtup = make_tuple(std::forward<Args>(args)...);
  // store this thing

And later to forward it with a bit of meta programming:

  template<int... Ints>
  struct int_pack {};

  template<int N, int... Tail>
  struct make_indices : make_indices<N-1,N-1,Tail...> {};

  template<int... Tail>
  struct make_indices<0,Tail...> {
    typedef int_pack<Tail...> type;

  template<class IntPack> struct invoke_helper;

  template<int... Indices>
  struct invoke_helper<int_pack<Indices...> > {
    template<class Func, class... T>
    static void doit(Func&& f, std::tuple<T...> const& a) {
    static void doit(Func&& f, std::tuple<T...> && a) {
        std::forward<typename std::tuple_element<Indices>::type>(
        // ^^^^^^^ (*)
    // (*): this is intentionally no std::move since one of
    // the Ts might be an lvalue reference.

  typedef decltype(argtup) argtup_type;
  constexpr int N = tuple_size<argtup_type>::value;
  typedef typename make_indices<N>::type indices;
  // no longer needed in thread/async ^^^ ^^^^^^
  // hence the std::move.



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