Tcl_SetVar and Looping

I have a Tcl/Tk GUI and a C library.

I can click a button on the GUI to call a C library function. The C
library function calculates a value, and writes the value back to an entry
box textvariable with Tcl_SetVar. This works great:

Tcl_SetVar(interp, "valAlignment", s, 0);

One of my C functions loops once a second, then writes back to 6 different
textvariables. I'm only seeing the updates from the loops maybe once every
10 seconds. Is there a way "flush" Tcl_SetVar from the C library, so that
I see every update?

Thanks,
Randy