std::unique_lock::lock - cppreference.com (original) (raw)

The following example uses lock to re-acquire a mutex that was unlocked.

#include #include #include #include #include   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 operation std::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: 1 1, initial counter: 2 2, initial counter: 3 3, initial counter: 4 4, initial counter: 5 5, initial counter: 6 6, initial counter: 7 7, initial counter: 8 8, initial counter: 9 9, initial counter: 10 6, final counter: 11 3, final counter: 12 4, final counter: 13 2, final counter: 14 5, final counter: 15 0, final counter: 16 1, final counter: 17 7, final counter: 18 9, final counter: 19 8, final counter: 20