std::unique_lock<Mutex>::try_lock

#include <chrono>
#include <iostream>
#include <mutex>
#include <thread>
#include <vector>
 
using namespace std::chrono_literals;
 
int main()
{
 std::mutex counter_mutex;
 std::vector <std::thread > threads;
 using Id = int;
 
 auto worker_task = [&](Id id, std::chrono::seconds wait, std::chrono::seconds acquire)
 {
 // wait for a few seconds before acquiring lock.
 std::this_thread::sleep_for (wait);
 
 std::unique_lock <std::mutex > lock(counter_mutex, std::defer_lock );
 if (lock.try_lock())
 std::cout << '#' << id << ", lock acquired.\n";
 else
 {
 std::cout << '#' << id << ", failed acquiring lock.\n";
 return;
 }
 
 // keep the lock for a while.
 std::this_thread::sleep_for (acquire);
 
 std::cout << '#' << id << ", releasing lock (via destructor).\n";
 };
 
 threads.emplace_back(worker_task, Id{0}, 0s, 2s);
 threads.emplace_back(worker_task, Id{1}, 1s, 0s);
 threads.emplace_back(worker_task, Id{2}, 3s, 0s);
 
 for (auto& thread : threads)
 thread.join();
}

#0, lock acquired.
#1, failed acquiring lock.
#0, releasing lock (via destructor).
#2, lock acquired.
#2, releasing lock (via destructor).