https://invisible-island.net/xterm/xtoolkit/
XtProcessLock, XtProcessUnlock - lock and unlock process
#include <X11/Intrinsic.h>
void XtProcessLock(void);
void XtProcessUnlock(void);
XtProcessLock is used to lock all process global data.
XtProcessUnlock unlocks the process.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.3.1 XtProcessLock(3)