std::try_lock

#include <chrono>
#include <functional>
#include <iostream>
#include <mutex>
#include <thread>
#include <vector>
 
int main()
{
 int foo_count = 0;
 std::mutex foo_count_mutex;
 int bar_count = 0;
 std::mutex bar_count_mutex;
 int overall_count = 0;
 bool done = false;
 std::mutex done_mutex;
 
 auto increment = [](int& counter, std::mutex & m, const char* desc)
 {
 for (int i = 0; i < 10; ++i)
 {
 std::unique_lock <std::mutex > lock(m);
 ++counter;
 std::cout << desc << ": " << counter << '\n';
 lock.unlock();
 std::this_thread::sleep_for (std::chrono::seconds (1));
 }
 };
 
 std::thread increment_foo(increment, std::ref (foo_count), 
 std::ref (foo_count_mutex), "foo");
 std::thread increment_bar(increment, std::ref (bar_count), 
 std::ref (bar_count_mutex), "bar");
 
 std::thread update_overall([&]()
 {
 done_mutex.lock();
 while (!done)
 {
 done_mutex.unlock();
 int result = std::try_lock(foo_count_mutex, bar_count_mutex);
 if (result == -1)
 {
 overall_count += foo_count + bar_count;
 foo_count = 0;
 bar_count = 0;
 std::cout << "overall: " << overall_count << '\n';
 foo_count_mutex.unlock();
 bar_count_mutex.unlock();
 }
 std::this_thread::sleep_for (std::chrono::seconds (2));
 done_mutex.lock();
 }
 done_mutex.unlock();
 });
 
 increment_foo.join();
 increment_bar.join();
 done_mutex.lock();
 done = true;
 done_mutex.unlock();
 update_overall.join();
 
 std::cout << "Done processing\n"
 << "foo: " << foo_count << '\n'
 << "bar: " << bar_count << '\n'
 << "overall: " << overall_count << '\n';
}

bar: 1
foo: 1
foo: 2
bar: 2
foo: 3
overall: 5
bar: 1
foo: 1
bar: 2
foo: 2
bar: 3
overall: 10
bar: 1
foo: 1
bar: 2
foo: 2
overall: 14
bar: 1
foo: 1
bar: 2
overall: 17
foo: 1
bar: 1
foo: 2
overall: 20
Done processing
foo: 0
bar: 0
overall: 20