In boost::log documentation, there's some code as following: * typedef attrs::mutable_constant< int > int_constant_t; boost::shared_ptr< int_constant_t > attr(new int_constant_t(-5)); lg.add_attribute("MyInteger", attr); BOOST_LOG(lg) << "This record has MyInteger == -5"; **// Change the attribute value attr->set_value(100); BOOST_LOG(lg) << "This record has MyInteger == 100"; * Now I have a situation in my multi-threading app: the 'attr->set_value()' could be called in different threads, so the following 'BOOST_LOG(lg)...' could access wrong attributes that is set by another thread. If I use a mutex to protect this, it would be stupid, because the log line might be filtered out, that means the 'locking mutex' is not neccessary. Who can help ? Jinqiang *btw, the boost::log documentation isn't too good, when I read it, I felt I lost in a juggle.*