C++: What is std::thread and how do you use it?

1#include <thread>
2#include <iostream>
3
4void worker(int id) {
5    std::cout << "Thread " << id << "\n";
6}
7
8int main() {
9    // Create and run thread
10    std::thread t1(worker, 1);
11
12    // Lambda
13    std::thread t2([]{
14        std::cout << "Lambda thread\n";
15    });
16
17    // Must join or detach
18    t1.join();
19    t2.join();
20
21    // Hardware concurrency
22    std::cout << std::thread::hardware_concurrency();
23
24    return 0;
25}
26
27// C++20: std::jthread (auto-join)
28std::jthread jt([](std::stop_token stoken) {
29    while (!stoken.stop_requested()) {
30        // Work
31    }
32});
33// Auto-joined on destruction