GFileDescriptorBased is implemented by streams (implementations of
gio.InputStream or gio.OutputStream) that are based on file descriptors.
Note that <gio/gfiledescriptorbased.h> belongs to the UNIX-specific
GIO interfaces, thus you have to use the gio-unix-2.0.pc pkg-config
file when using it.
Gets the underlying file descriptor.
Get the main Gtk struct
the main Gtk struct as a void*