Generally, functions in the UCW library are reentrant as long as you call them on different data. Calling on the same object is not, unless otherwise told, which also includes functions acting on any kind of global state. There are some exceptions: - logging functions are safe as long as you don't switch log files - setproctitle() is not safe, it modifies global state - handle_signal() is not safe, it modifies global state - stk_printf() is not safe, it currently uses a global buffer (FIXME!)