NDC

Section: User Contributed Perl Documentation (3)
Updated: 2021-02-08
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NAME

Log::Log4perl::NDC - Nested Diagnostic Context

DESCRIPTION

Log::Log4perl allows loggers to maintain global thread-specific data, called the Nested Diagnostic Context (NDC).

At some point, the application might decide to push a piece of data onto the NDC stack, which other parts of the application might want to reuse. For example, at the beginning of a web request in a server, the application might decide to push the IP address of the client onto the stack to provide it for other loggers down the road without having to pass the data from function to function.

The Log::Log4perl::Layout::PatternLayout class even provides the handy %x placeholder which is replaced by the blank-separated list of elements currently on the stack.

This module maintains a simple stack which you can push data on to, query what's on top, pop it off again or delete the entire stack.

Its purpose is to provide a thread-specific context which all Log::Log4perl loggers can refer to without the application having to pass around the context data between its functions.

Since in 5.8.0 perl's threads don't share data only upon request, global data is by definition thread-specific.

Log::Log4perl::NDC->push($text);: Push an item onto the stack. If the stack grows beyond the defined limit ($Log::Log4perl::NDC::MAX_SIZE), just the topmost element will be replated.
This is typically done when a context is entered.
Log::Log4perl::NDC->pop();: Discard the upmost element of the stack. This is typically done when a context is left.
my $text = Log::Log4perl::NDC->get();: Retrieve the content of the stack as a string of blank-separated values without disrupting the stack structure. Typically done by %x. If the stack is empty the value "[undef]" is being returned.
Log::Log4perl::NDC->remove();: Reset the stack, remove all items.

Please note that all of the methods above are class methods, there's no instances of this class.

LICENSE

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

AUTHOR

Please contribute patches to the project on Github:

    http://github.com/mschilli/log4perl

Send bug reports or requests for enhancements to the authors via our

MAILING LIST (questions, bug reports, suggestions/patches): log4perl-devel@lists.sourceforge.net

Authors (please contact them via the list above, not directly): Mike Schilli <m@perlmeister.com>, Kevin Goess <cpan@goess.org>

Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier David Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter, Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars Thegler, David Viner, Mac Yang.