PureGDK can compile to a threadsafe executable by using the PureGDKThreadSafe subsystem. Add this subsystem to your project under Compiler -> Compiler Options when compiling with threadsafe to use it. Plugins must be compiled using Tailbite to both normal and threadsafe libraries to be supported by the threadsafe subsystem.
PureGDK executables compiled with this subsystem are threadsafe in that commands can be called from a thread safely. It does not provide any method of preventing collisions if you should happen to call a PureGDK command from more than one thread at a time. In this case use a mutex or keep your PureGDK commands exclusive to a single thread.