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 1.1.5.2 XtProcessLock(3)