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'\" Copyright (c) 1990 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\" RCS: @(#) $Id: CrtTimerHdlr.3,v 1.1.1.1 2002-01-16 10:25:23 markom Exp $
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.so man.macros
.TH Tcl_CreateTimerHandler 3 7.5 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_CreateTimerHandler, Tcl_DeleteTimerHandler \- call a procedure at a
given time
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_TimerToken
\fBTcl_CreateTimerHandler\fR(\fImilliseconds, proc, clientData\fR)
.sp
\fBTcl_DeleteTimerHandler\fR(\fItoken\fR)
.SH ARGUMENTS
.AS Tcl_TimerToken milliseconds
.AP int milliseconds  in
How many milliseconds to wait before invoking \fIproc\fR.
.AP Tcl_TimerProc *proc in
Procedure to invoke after \fImilliseconds\fR have elapsed.
.AP ClientData clientData in
Arbitrary one-word value to pass to \fIproc\fR.
.AP Tcl_TimerToken token in
Token for previously-created timer handler (the return value
from some previous call to \fBTcl_CreateTimerHandler\fR).
.BE

.SH DESCRIPTION
.PP
\fBTcl_CreateTimerHandler\fR arranges for \fIproc\fR to be
invoked at a time \fImilliseconds\fR milliseconds in the
future.
The callback to \fIproc\fR will be made by \fBTcl_DoOneEvent\fR,
so \fBTcl_CreateTimerHandler\fR is only useful in programs that
dispatch events through \fBTcl_DoOneEvent\fR or through Tcl commands
such as \fBvwait\fR.
The call to \fIproc\fR may not be made at the exact time given by
\fImilliseconds\fR:  it will be made at the next opportunity
after that time.  For example, if \fBTcl_DoOneEvent\fR isn't
called until long after the time has elapsed, or if there
are other pending events to process before the call to
\fIproc\fR, then the call to \fIproc\fR will be delayed.
.PP
\fIProc\fR should have arguments and return value that match
the type \fBTcl_TimerProc\fR:
.CS
typedef void Tcl_TimerProc(ClientData \fIclientData\fR);
.CE
The \fIclientData\fR parameter to \fIproc\fR is a
copy of the \fIclientData\fR argument given to
\fBTcl_CreateTimerHandler\fR when the callback
was created.  Typically, \fIclientData\fR points to a data
structure containing application-specific information about
what to do in \fIproc\fR.
.PP
\fBTcl_DeleteTimerHandler\fR may be called to delete a
previously-created timer handler.  It deletes the handler
indicated by \fItoken\fR so that no call to \fIproc\fR
will be made;  if that handler no longer exists
(e.g. because the time period has already elapsed and \fIproc\fR
has been invoked then \fBTcl_DeleteTimerHandler\fR does nothing.
The tokens returned by \fBTcl_CreateTimerHandler\fR never have
a value of NULL, so if NULL is passed to \fBTcl_DeleteTimerHandler\fR
then the procedure does nothing.

.SH KEYWORDS
callback, clock, handler, timer