38     int ec = __libcpp_mutex_lock(&__m_);  in lock()  local
39     if (ec)  in lock()
40         __throw_system_error(ec, "mutex lock failed");  in lock()
52     int ec = __libcpp_mutex_unlock(&__m_);  in unlock()  local
53     (void)ec;  in unlock()
54     _LIBCPP_ASSERT(ec == 0, "call to mutex::unlock failed");  in unlock()
61     int ec = __libcpp_recursive_mutex_init(&__m_);  in recursive_mutex()  local
62     if (ec)  in recursive_mutex()
63         __throw_system_error(ec, "recursive_mutex constructor failed");  in recursive_mutex()
76     int ec = __libcpp_recursive_mutex_lock(&__m_);  in lock()  local
77     if (ec)  in lock()
78         __throw_system_error(ec, "recursive_mutex lock failed");  in lock()