Async and function implementation in C++

async.cc

#include <iostream>
#include <cstdlib>
#include <unistd.h> //for sleep
#include <future>
#include <map>

using namespace std;

map<string,function<void()>> my_functions = {
  
  { "test", [](){
    cout << "test function" << endl;
  }},
  
  { "long", [](){
    cout << "long: before loop" << endl;
    for (int i = 0; i < 1e9; i++){}
    cout << "long: after loop" << endl;
  }},
  
};

int main(int argc, const char * argv[]){
  
  future<void> a(async(my_functions["long"]));
  
  my_functions["test"]();
  
  a.get();
  
  return 0;
  
}