何时std :: lock_guard被锁定？

Question

我有以下代码。我想知道scoped锁是否在函数“do_something”的开头被锁定了？非常感谢！

class Test {
public:
    void do_something () {
        std::cout << "anything printable" << std::endl;
        // do something else
        // Has mu_ got locked here?
        ...

        std::lock_guard<std::mutex> l(mu_);
        // something only I can do
        ...

        return;
    }
private:
    std::mutex mu_;
}