On Wed, 12 Nov 2008, Anatoliy wrote:
> I'm going to use POE library for performing multitasks and I'd like to
> use POEs session specific values in the MDC.
>
> POE doesn't use threads/processes, so I can't make it with global variables.
> Is there any thing equal to MDC but for using with $logger object? not
> Log::Log4perl class. Thank you for Log::Log4perl anyway :)
You're welcome, and that's a very good question, I've added an anwer to
the FAQ and made some changes to Log4perl:
=head2 How can I access POE heap values from Log4perl's layout?
POE is a framework for creating multitasked applications running in a
single process and a single thread. POE's threads equivalents are
'sessions' and since they run quasi-simultaneously, you can't use
Log4perl's global NDC/MDC to hold session-specific data.
However, POE already maintains a data store for every session. It is called
'heap' and is just a hash storing session-specific data in key-value pairs.
To access this per-session heap data from a Log4perl layout, define a
custom cspec and reference it with the newly defined pattern in the layout:
use strict;
use POE;
use Log::Log4perl qw(:easy);
Log::Log4perl->init( \ q{
log4perl.logger = DEBUG, Screen
log4perl.appender.Screen = Log::Log4perl::Appender::Screen
log4perl.appender.Screen.layout = PatternLayout
log4perl.appender.Screen.layout.ConversionPattern = %U %m%n
log4perl.PatternLayout.cspec.U = \
sub { POE::Kernel->get_active_session->get_heap()->{ user } }
} );
for (qw( Huey Lewey Dewey )) {
POE::Session->create(
inline_states => {
_start => sub {
$_[HEAP]->{user} = $_;
POE::Kernel->yield('hello');
},
hello => sub {
DEBUG "I'm here now";
}
}
);
}
POE::Kernel->run();
exit;
The code snippet above defines a new layout placeholder (called
'cspec' in Log4perl) %U which calls a subroutine, retrieves the active
session, gets its heap and looks up the entry specified ('user').
Starting with Log::Log4perl 1.20, cspecs also support parameters in
curly braces, so you can say
log4perl.appender.Screen.layout.ConversionPattern = %U{user} %U{id} %m%n
log4perl.PatternLayout.cspec.U = \
sub { POE::Kernel->get_active_session-> \
get_heap()->{ $_[0]->{curlies} } }
and print the POE session heap entries 'user' and 'id' with every logged
message. For more details on cpecs, read the PatternLayout manual.
Hope that helps!
-- Mike
Mike Schilli
[EMAIL PROTECTED]
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