#include <chrono>#include <iostream>#include <mutex>#include <thread>#include <vector> int main(){int counter=0;std::mutex counter_mutex;std::vector<std::thread> threads; auto worker_task=[&](int id){std::unique_lock<std::mutex> lock(counter_mutex);++counter;std::cout<< id<<", initial counter: "<< counter<<'\n';        lock.unlock(); // don't hold the lock while we simulate an expensive operationstd::this_thread::sleep_for(std::chrono::seconds(1));         lock.lock();++counter;std::cout<< id<<", final counter: "<< counter<<'\n';}; for(int i=0; i<10;++i)        threads.emplace_back(worker_task, i); for(auto& thread: threads)        thread.join();}

0, initial counter: 11, initial counter: 22, initial counter: 33, initial counter: 44, initial counter: 55, initial counter: 66, initial counter: 77, initial counter: 88, initial counter: 99, initial counter: 106, final counter: 113, final counter: 124, final counter: 132, final counter: 145, final counter: 150, final counter: 161, final counter: 177, final counter: 189, final counter: 198, final counter: 20