NAME

Tcl_CreateModalTimeout, Tcl_DeleteModalTimeout - special timer for modal operations

SYNOPSIS

#include <tcl.h>
Tcl_CreateModalTimeout(milliseconds, proc, clientData)
Tcl_DeleteModalTimeout(proc, clientData)

ARGUMENTS

int milliseconds (in)
How many milliseconds to wait before invoking proc.

Tcl_TimerProc *proc (in)
Procedure to invoke after milliseconds have elapsed.

ClientData clientData (in)
Arbitrary one-word value to pass to proc.

DESCRIPTION

Tcl_CreateModalTimeout provides an alternate form of timer from those provided by Tcl_CreateTimerHandler. These timers are called ``modal'' because they are typically used in situations where a particular operation must be completed before the application does anything else. If such an operation needs a timeout, it cannot use normal timer events: if normal timer events were processed, arbitrary Tcl scripts might be invoked via other event handlers, which could interfere with the completion of the modal operation. The purpose of modal timers is to allow a single timeout to occur without allowing any normal timer events to occur.

Tcl_CreateModalTimeout behaves just like Tcl_CreateTimerHandler except that it creates a modal timeout. Its arguments have the same meaning as for Tcl_CreateTimerHandler and proc is invoked just as for Tcl_CreateTimerHandler. Tcl_DeleteModalTimeout deletes the most recently created modal timeout; its arguments must match the corresponding arguments to the most recent call to Tcl_CreateModalTimeout.

Modal timeouts differ from a normal timers in three ways. First, they will trigger regardless of whether the TCL_TIMER_EVENTS flag has been passed to Tcl_DoOneEvent. Typically modal timers are used with the TCL_TIMER_EVENTS flag off so that normal timers don't fire but modal ones do. Second, if several modal timers have been created they stack: only the top timer on the stack (the most recently created one) is active at any point in time. Modal timeouts must be deleted in inverse order from their creation. Third, modal timeouts are not deleted when they fire: once a modal timeout has fired, it will continue firing every time Tcl_DoOneEvent is called, until the timeout is deleted by calling Tcl_DeleteModalTimeout.

Modal timeouts are only needed in a few special situations, and they should be used with caution.

KEYWORDS

callback, clock, handler, modal timeout 
Copyright © 1995-1996 Sun Microsystems, Inc.
Copyright © 1995, 1996 Roger E. Critchlow Jr.