Using replace() in multi-threaded environment

1#include <algorithm>
2#include <iostream>
3#include <thread>
4#include <mutex>
5#include <vector>
6
7std::mutex mtx;
8
9void replace_elements(
10  std::vector<int> &data,
11  int old_value,
12  int new_value
13) {
14  std::lock_guard<std::mutex> lock(mtx);
15  std::ranges::replace(data, old_value, new_value);
16}
17
18int main() {
19  std::vector<int> data{1, 2, 3, 3, 3, 4, 5};
20
21  std::thread t1(
22    replace_elements, std::ref(data), 3, 0);
23  std::thread t2(
24    replace_elements, std::ref(data), 4, 9);
25
26  t1.join();
27  t2.join();
28
29  std::cout << "Modified data: ";
30  for (const auto &num : data) {
31    std::cout << num << ", ";
32  }
33}

1#include <algorithm>
2#include <iostream>
3#include <thread>
4#include <vector>
5
6void replace_elements(
7  const std::vector<int> &source,
8  std::vector<int> &dest,
9  int old_value,
10  int new_value
11) {
12  std::ranges::replace_copy(
13    source, dest.begin(), old_value, new_value);
14}
15
16int main() {
17  std::vector<int> data{1, 2, 3, 3, 3, 4, 5};
18  std::vector<int> result1(
19    data.size()), result2(data.size());
20
21  std::thread t1(replace_elements,
22    std::cref(data), std::ref(result1), 3, 0);
23  std::thread t2(replace_elements,
24    std::cref(data), std::ref(result2), 4, 9);
25
26  t1.join();
27  t2.join();
28
29  std::cout << "Result 1: ";
30  for (const auto &num : result1) {
31    std::cout << num << ", ";
32  }
33  std::cout << "\nResult 2: ";
34  for (const auto &num : result2) {
35    std::cout << num << ", ";
36  }
37}