DOKK / manpages / debian 11 / libx11-doc / XSetAfterFunction.3.en
XSynchronize(3) XLIB FUNCTIONS XSynchronize(3)

XSynchronize, XSetAfterFunction - enable or disable synchronization

int (*XSynchronize(Display *display, Bool onoff))();

int (*XSetAfterFunction(Display *display, int (*procedure)()))();

Specifies the connection to the X server.
Specifies the procedure to be called.
Specifies a Boolean value that indicates whether to enable or disable synchronization.

The XSynchronize function returns the previous after function. If onoff is True, XSynchronize turns on synchronous behavior. If onoff is False, XSynchronize turns off synchronous behavior.

The specified procedure is called with only a display pointer. XSetAfterFunction returns the previous after function.

XSetErrorHandler(3)
Xlib - C Language X Interface

libX11 1.7.2 X Version 11