XtNoticeSignal(3) register and remove a signal source

Other Alias

XtAppAddSignal, XtRemoveSignal


XtSignalId XtAppAddSignal(XtAppContext app_context, XtSignalCallbackProc proc, XtPointer client_data);
void XtRemoveSignal(XtSignalId id);
void XtNoticeSignal(XtSignalId id);


Specifies the application context.
Specifies the argument that is to be passed to the specified procedure when a signal has been raised.
Specifies the ID returned from the corresponding XtAppAddSignal call.
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.