TIP:            245
Title:          Discover User Inactivity Time
Version:        $Revision: 1.12 $
Author:         Pascal Scheffers <pascal@scheffers.net>
Author:         Reinhard Max <max@tclers.tk>
Author:         Neil Madden <nem@cs.nott.ac.uk>
State:          Final
Type:           Project
Vote:           Done
Created:        15-Apr-2005
Post-History:   
Keywords:       Tk
Tcl-Version:    8.5

~ Abstract

This TIP proposes a new subcommand, '''inactive''', to the '''tk'''
command, as well as '''Tk_GetUserInactiveTime''' and '''Tk_ResetUserInactiveTime''' C functions to discover
the number of milliseconds the user has been inactive and reset that timer to zero respectively. For most environments, this is the time since the user last used the keyboard
or mouse.

~ Rationale

User inactivity is used by screen-savers, chat applications and for
security conscious applications to quit or lock themselves after some
inactive time has elapsed. It would make it easier for authors of
these kinds of applications to use Tk if there was a simple way to get
the length of time which the user has been inactive, which is
information available on all supported platforms.

Applications that take some kind of user input from channels that bypass the system's mechanisms for detecting user activity might want to tell the system to reset the inactivity timer because they received input that has to be treated as user activity. An example for this would be barcode readers connected via serial lines that are read directly by the application.

~ Specification

~~ Tcl API

A single new subcommand will be added to '''tk''',
'''inactive'''. This command takes an optional argument
?'''-displayof''' ''window''?. It returns a positive integer, the
number of milliseconds since the last time the user interacted with
the system. If the -displayof option is given then the return value
refers to the display of ''window''; otherwise it refers to the
display of the application's main window.

If querying the user inactive time is not supported by the system,
'''tk inactive''' will return -1.

If the literal string '''reset''' is given as an additional argument, the timer is reset and an empty string is returned.

 > '''tk''' '''inactive''' ?'''-displayof''' ''window''? ?'''reset'''?

~~ C API

long '''Tk_GetUserInactiveTime'''(''display'')

 Display *display (in): used to determine which display to query for
    user inactive time.

'''Tk_GetUserInactiveTime()''' returns a positive integer, the number of
milliseconds since the last time the user interacted with the system
(note that this is not necessarily the time since the user interacted
with the application.)

void '''Tk_ResetUserInactiveTime'''(''display'')

 Display *display (in): used to determine on which display the user inactivity timer is to be reset.

~ Safe Interpreters

User inactive time can be used for timing attacks and will not be made
available in safe interpreters, '''tk inactive''' will return -1 in
safe interpreters. Calling '''tk inactive reset''' in a safe interpreter will throw an error.

~ Implementation Notes

Windows 2000 and later have ''GetLastInputInfo'' to obtain the
information, earlier platforms do not have this symbol in user32.dll.
This symbol will be dynamically obtained upon the first call of
''Tk_UserInactiveTime()'' on windows. If the symbol is not available,
''Tk_UserInactiveTime()'' will return -1. ''GetLastInputInfo()'' has no
notion of displays, and as a result the display argument is
ignored. The behaviour of the command is unknown for terminal
services, remote desktop, VNC, Citrix and other remote screen systems.

For X, this patch introduces two additional library dependencies -
libXext and libXss. The authors do not know if a similar situation to
Windows could exist on the X Window System, where the build host has
libXss, and yet not all installations for that platform have libXss. A
proper solution for that scenario would require an additional TIP to
export TclLoadFile, Tcl_FSLoadFile is not sufficient, to resolve the
symbols at runtime. (The other library, libXext, is virtually
universally available.)

For Win9x, Microsoft has published example code at [http://www.microsoft.com/msj/0200/c/c0200.aspx].

~ Reference Implementation

A reference implementation is available as Patch #1185731 on
SourceForge[http://sf.net/support/tracker.php?aid=1185731].

~ Comments

[[ Insert here please ]]

~ Copyright

This document has been placed in the public domain.
