Search⌘ K
Home
Courses
C++ Fundamentals for Professionals

- Solution

Explore how the std::thread::hardware_concurrency function in C++11 helps detect the number of CPU cores available. Understand how to handle cases where no core count is provided and adapt your programs dynamically to optimize performance based on hardware capabilities. This lesson prepares you for advanced task management with promises and futures.

We'll cover the following...

Solution #

C++ 17
#include <algorithm>
#include <future>
#include <iostream>
#include <thread>
#include <deque>
#include <vector>
class SumUp{
public:
  SumUp(int b, int e): beg(b), end(e){}
  int operator()(){
    long long int sum{0};
    for (int i= beg; i < end; ++i ) sum += i;
    return sum;
  }
private:
    int beg;
    int end;
};
static const unsigned int hwGuess = 4;
static const unsigned int numbers = 10001;
int main(){
  std::cout << std::endl;
  unsigned int hw = std::thread::hardware_concurrency();
  unsigned int hwConcurr = (hw != 0)? hw : hwGuess;
  // define the functors
  std::vector<SumUp> sumUp;
  for (unsigned int i = 0; i < hwConcurr; ++i){
    int begin = (i*numbers)/hwConcurr;
    int end = (i+1)*numbers/hwConcurr;
    sumUp.push_back(SumUp(begin , end));
  }
  // define the tasks
  std::deque<std::packaged_task<int()>> sumTask;
  for (unsigned int i = 0; i < hwConcurr; ++i){
    std::packaged_task<int()> SumTask(sumUp[i]);
    sumTask.push_back(std::move(SumTask));
  }
  // get the futures
  std::vector< std::future<int>> sumResult;
  for (unsigned int i = 0; i < hwConcurr; ++i){
    sumResult.push_back(sumTask[i].get_future());
  }
  // execute each task in a separate thread
  while (! sumTask.empty()){
    std::packaged_task<int()> myTask = std::move(sumTask.front());
    sumTask.pop_front();
    std::thread sumThread(std::move(myTask));
    sumThread.detach();
  }
  // get the results
  int sum = 0;
  for (unsigned int i = 0; i < hwConcurr; ++i){
    sum += sumResult[i].get();
  }
  std::cout << "sum of 0 .. 100000 = " << sum << std::endl;
  std::cout << std::endl;
}

Explanation

...