Writing GLib Applications
Writing GLib Applications — General considerations when programming with GLib
The general policy of GLib is that all functions are invisibly threadsafe with the exception of data structure manipulation functions, where, if you have two threads manipulating the same data structure, they must use a lock to synchronize their operation.
GLib creates a worker thread for its own purposes so GLib applications will always have at least 2 threads.
When writing code that runs with elevated privileges, it is important to follow some basic rules of secure programming. David Wheeler has an excellent book on this topic, Secure Programming for Linux and Unix HOWTO.
When it comes to GLib and its associated libraries, GLib and GObject are generally fine to use in code that runs with elevated privileges; they don't load modules (executable code in shared objects) or run other programs 'behind your back'. GIO has to be used carefully in privileged programs, see the GIO documentation for details.