https://invisible-island.net/xterm/xtoolkit/
XtAppAddSignal, XtRemoveSignal, XtNoticeSignal - register and remove a
signal source
#include <X11/Intrinsic.h>
XtSignalId XtAppAddSignal(XtAppContext app_context, XtSignalCallback-
Proc proc, XtPointer client_data);
void XtRemoveSignal(XtSignalId id);
void XtNoticeSignal(XtSignalId id);
app_context
Specifies the application context.
client_data
Specifies the argument that is to be passed to the specified
procedure when a signal has been raised.
id Specifies the ID returned from the corresponding XtAppAdd-
Signal call.
proc Specifies the procedure that is to be called when the signal
has been raised.
The XtAppAddSignal function initiates a mechanism for handling signals
within the context of the Intrinsics. Prior to establishing an operat-
ing system dependent signal handler the application may call XtAppAdd-
Signal and store the returned id in a place accessible to the signal
handler.
Upon receipt of a signal from the operating system, the application may
call XtNoticeSignal passing the id returned by the call to XtAppAdd-
Signal.
XtNoticeSignal is the only Intrinsics function that can safely be
called from a signal handler. If XtNoticeSignal is called multiple
times before the Intrinsics are able to invoke the registered callback,
the callback is only called once. Logically the Intrinsics maintain
"pending" for each registered callback. This flag is initially False
and is set to True by XtNoticeSignal; the Intrinsics invoke the call-
back whenever the flag is True, and the flag is set to False just
before the callback is invoked.
The XtRemoveSignal function is called to remove the specified Intrin-
sics signal handler. The client should disable the source of the sig-
nal before calling XtRemoveSignal.
XtAppAddTimeOut(3),XtAppAddInput(3),XtAppAddWorkProc(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtAppAddSignal(3)