Tie::Scalar::Timeout - Scalar variables that time out


  use Tie::Scalar::Timeout;

  tie my $k, 'Tie::Scalar::Timeout', EXPIRES => '+2s';

  $k = 123;
  # $k is now undef

  tie my $m, 'Tie::Scalar::Timeout', NUM_USES => 3, VALUE => 456;

  tie my $n, 'Tie::Scalar::Timeout', VALUE => 987, NUM_USES => 1,
      POLICY => 777;

  tie my $p, 'Tie::Scalar::Timeout', VALUE => 654, NUM_USES => 1,
      POLICY => \&expired;
  sub expired { $is_expired++ }


This module allows you to tie a scalar variable whose value will be reset (subject to an expiry policy) after a certain time and/or a certain number of uses. One possible application for this module might be to time out session variables in mod_perl programs.

When tying, you can specify named arguments in the form of a hash. The following named parameters are supported:

Use EXPIRES to specify an interval or absolute time after which the value will be reset. (Technically, the value will still be there, but the module's FETCH sub will return the value as dictated by the expiry policy.)

Values for the EXPIRES field are modelled after Netscape's cookie expiration times. Except, of course, that negative values don't really make sense in a universe with linear, one-way time. The following forms are all valid for the EXPIRES field:

    +30s                    30 seconds from now
    +10m                    ten minutes from now
    +1h                     one hour from now
    +3M                     in three months
    +10y                    in ten years time
    25-Apr-2001 00:40:33    at the indicated time & date

Assigning a value to the variable causes EXPIRES to be reset to the original value.

Using the VALUE hash key, you can specify an initial value for the variable.

Alternatively or in addition to EXPIRES, you can also specify a maximum number of times the variable may be read from before it expires. If both EXPIRES and NUM_USES are set, the variable will expire when either condition becomes true. If NUM_USES isn't set or set to a negative value, it won't influence the expiry process.

Assigning a value to the variable causes NUM_USES to be reset to the original value.

The expiration policy determines what happens to the variable's value when it expires. If you don't specify a policy, the variable will be undef after it has expired. You can specify either a scalar value or a code reference as the value of the POLICY parameter. If you specify a scalar value, that value will be returned after the variable has expired. Thus, the default expiration policy is equivalent to
    POLICY => undef

If you specify a code reference as the value of the POLICY parameter, that code will be called when the variable value is FETCH()ed after it has expired. This might be used to set some other variable, or reset the variable to a different value, for example.


None known so far. If you find any bugs or oddities, please do tell me about them.


Marcel Grünauer <marcel@codewerk.com>


Copyright 2000 Marcel Grünauer. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


perl(1), Tie::Scalar(3pm).