Question about reading.

my code is that first reading a file and show the file graphically with glut.
everything works well.
However, some of file size is over 2G then first reading is extremely slow. How can I make better this problem?

some of friends said use Timer or Thread.
which one is better?
and I’ve hardly found example code about Timer or Thread on linux almost all examples on web is for windows.

Can you help me? and suggest sites?

What are you drawing with OpenGL? What kind of files are these?