xnoop(3x11) [osf1 man page]
XNoOp(3X11) XNoOp(3X11) NAME
XNoOp - No Operation SYNOPSIS
XNoOp(display) Display *display; ARGUMENTS
Specifies the connection to the X server. DESCRIPTION
The XNoOp function sends a NoOperation protocol request to the X server, thereby exercising the connection. SEE ALSO
Xlib -- C Language X Interface XNoOp(3X11)