no matching constructor for initialization of 'std::thread'

Question

I have been working on a rather simple facility: a concurrent for loop construct that takes a list of input elements, an output vector, and a function that computes output elements out of input elements.

I have this snippet that does not compile:

            template<class In, class Out>
            void thread_do(net::coderodde::concurrent::queue<In>& input_queue,
                           Out (*process)(In in),
                           std::vector<Out>& output_vector)
            {
                // Pop the queue, process, and save result.
                ...
            }


                for (unsigned i = 0; i < thread_count; ++i) 
                {
                    thread_vector.push_back(std::thread(thread_do, 
                                                        input_queue,
                                                        process,
                                                        output_vector));
                }

I use -std=c++14 .

However, I have no idea how to fix it. Tried to prepend & to the thread_do /appending <In, Out> , yet no to avail.

Answer 1

This minimal, complete example (hint) shows you how to call a template member function in another thread.

#include <thread>

struct X
{

  template<class A, class B> void run(A a, B b)
  {
  }

  template<class A, class B>
  void run_with(A a, B b)
  {
    mythread = std::thread(&X::run<A, B>, this, a, b);
  }

  std::thread mythread;
};

int main()
{
  X x;
  x.run_with(10, 12);
  x.mythread.join();
}

Note that std::thread 's constructor is not able to auto-deduce template arguments. You have to be explicit.

Answer 2

You need to instantiate your function:

thread_vector.push_back(std::thread(thread_do<In, Out>,     // you need to instantiate your template function 
                                    std::ref(input_queue),  // pass parameters by ref 
                                    std::ref(process),      // - // -
                                    std::ref(output_vector))// - // -
                                    );