XtAppAddSignal, XtRemoveSignal, XtNoticeSignal - register and remove a signal source

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 XtAppAddSignal 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 operating system dependent signal handler the application may call
       XtAppAddSignal 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 XtAppAddSignal.

       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
       callback 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  Intrinsics  signal  handler.   The  client
       should disable the source of the signal before calling XtRemoveSignal.

       XtAppAddSignal, XtRemoveSignal, XtNoticeSignal - register and remove a signal source

XtAppAddTimeOut(3),XtAppAddInput(3),XtAppAddWorkProc(3)
       XToolkitIntrinsics-CLanguageInterfaceXlib-CLanguageXInterface

X Version 11                                       libXt 1.2.1                                 XtAppAddSignal(3)

       #include <X11/Intrinsic.h>

       XtSignalId XtAppAddSignal(XtAppContext app_context, XtSignalCallbackProc proc, XtPointer client_data);

       void XtRemoveSignal(XtSignalId id);

       void XtNoticeSignal(XtSignalId id);