thread_pool

c++11 thread pool

####usage:

std::mutex mtx;
try{
	tp::thread_pool tp;
	std::vector<std::future<int>> v;
	std::vector<std::future<void>> v1;
	for (int i = 0; i != 10; ++i){
		auto ans = tp.submit([](int answer) { return answer; }, i);
		v.push_back(std::move(ans));
	}
	for (int i = 0; i != 5; ++i){
		auto ans = tp.submit([&mtx](const std::string& str1, const std::string& str2){
			std::lock_guard<std::mutex> lg(mtx);
			std::cout << (str1 + str2) << std::endl;
			return;
		}, "hello ", "world");
		v1.push_back(std::move(ans));
	}
	for (int i = 0; i != v.size(); ++i){
		std::lock_guard<std::mutex> lg(mtx);
		cout << v[i].get() << endl;
	}
	for (int i = 0; i != v1.size(); ++i){
		v1[i].get();
	}
}catch (std::exception& e){
	std::cout << e.what() << std::endl;
}