.\" $Xorg: XtAppASig.man,v 1.3 2000/08/17 19:41:57 cpqbld Exp $
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.ds tk X Toolkit
.ds xT X Toolkit Intrinsics \- C Language Interface
.ds xI Intrinsics
.ds xW X Toolkit Athena Widgets \- C Language Interface
.ds xL Xlib \- C Language X Interface
.ds xC Inter-Client Communication Conventions Manual
.ds Rn 3
.ds Vn 2.2
.hw XtApp-Add-Signal wid-get
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.TH XtAppAddSignal 3Xt __xorgversion__ "XT FUNCTIONS"
.SH NAME
XtAppAddSignal, XtRemoveSignal, XtNoticeSignal \- register and remove a signal source
.SH SYNTAX
.HP
XtSignalId XtAppAddSignal(XtAppContext \fIapp_context\fP, XtSignalCallbackProc
\fIproc\fP, XtPointer \fIclient_data\fP); 
.HP
void XtRemoveSignal(XtSignalId \fIid\fP); 
.HP
void XtNoticeSignal(XtSignalId \fIid\fP); 
.SH ARGUMENTS
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIclient_data\fP 1i
Specifies the argument that is to be passed to the specified procedure
when a signal has been raised.
.IP \fIid\fP 1i
Specifies the ID returned from the corresponding
.ZN XtAppAddSignal
call.
.IP \fIproc\fP 1i
Specifies the procedure that is to be called when the signal has been 
raised.
.SH DESCRIPTION
The
.ZN 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
.ZN XtAppAddSignal
and store the returned \fIid\fP in a place accessible to the signal 
handler.
.LP
Upon receipt of a signal from the operating system, the application may 
call 
.ZN XtNoticeSignal
passing the \fIid\fP returned by the call to
.ZN XtAppAddSignal .
.LP
.ZN XtNoticeSignal
is the only Intrinsics function that can safely be called from a signal
handler. If
.ZN 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
.ZN False
and is set to
.ZN True 
by
.ZN XtNoticeSignal ;
the Intrinsics invoke the callback whenever the flag is
.ZN True ,
and the flag is set to
.ZN False
just before the callback is invoked.
.LP
The
.ZN XtRemoveSignal
function is called to remove the specified Intrinsics signal handler. The 
client should disable the source of the signal before calling
.ZN XtRemoveSignal .
.SH "SEE ALSO"
XtAppAddTimeOut(3Xt),XtAppAddInput(3Xt),XtAppAddWorkProc(3Xt)
.br
\fI\*(xT\fP
.br
\fI\*(xL\fP