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Mike Schilli

NAME

Log::Log4perl::Config::Watch - Detect file changes

SYNOPSIS

    use Log::Log4perl::Config::Watch;

    my $watcher = Log::Log4perl::Config::Watch->new(
                          file            => "/data/my.conf",
                          check_interval  => 30,
                  );

    while(1) {
        if($watcher->change_detected()) {
            print "Change detected!\n";
            sleep(1);
        }
    }

DESCRIPTION

This module helps detecting changes in files. Although it comes with the Log::Log4perl distribution, it can be used independly.

The constructor defines the file to be watched and the check interval in seconds. Subsequent calls to change_detected() will

  • return a false value immediately without doing physical file checks if check_interval hasn't elapsed.

  • perform a physical test on the specified file if the number of seconds specified in check_interval have elapsed since the last physical check. If the file's modification date has changed since the last physical check, it will return a true value, otherwise a false value is returned.

Bottom line: check_interval allows you to call the function change_detected() as often as you like, without paying the performing a significant performance penalty because file system operations are being performed (however, you pay the price of not knowing about file changes until check_interval seconds have elapsed).

The module clearly distinguishes system time from file system time. If your (e.g. NFS mounted) file system is off by a constant amount of time compared to the executing computer's clock, it'll just work fine.

To disable the resource-saving delay feature, just set check_interval to 0 and change_detected() will run a physical file test on every call.

If you already have the current time available, you can pass it on to change_detected() as an optional parameter, like in

    change_detected($time)

which then won't trigger a call to time(), but use the value provided.

SIGNAL MODE

Instead of polling time and file changes, new() can be instructed to set up a signal handler. If you call the constructor like

    my $watcher = Log::Log4perl::Config::Watch->new(
                          file    => "/data/my.conf",
                          signal  => 'HUP'
                  );

then a signal handler like

    $SIG{HUP} = sub { $SIGNAL_CAUGHT = 1; };

will be installed, setting a globally accessible variable Log::Log4perl::Config::Watch::SIGNAL_CAUGHT to a true value when the signal arrives. Comes with all the problems that signal handlers go along with.

SEE ALSO

AUTHOR

    Mike Schilli, <log4perl@perlmeister.com>

COPYRIGHT AND LICENSE

Copyright 2003 by Mike Schilli <m@perlmeister.com> and Kevin Goess <cpan@goess.org>.

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