XSynchronize(), XSetAfterFunction() - enable or disable synchronization
int (Display *display, Bool onoff)
int (Display *display, int (* procedure)())
The XSynchronize(3) function returns the previous after function. If onoff is True, XSynchronize(3) turns on synchronous behavior. If onoff is False, XSynchronize(3) turns off synchronous behavior.
The specified procedure is called with only a display pointer. XSetAfterFunction(3) returns the previous after function.
Xlib