path: root/lib/Log/Log4perl/Appender/Buffer.pm

######################################################################
# Buffer.pm -- 2004, Mike Schilli <m@perlmeister.com>
######################################################################
# Composite appender buffering messages until a trigger condition is met.
######################################################################

###########################################
package Log::Log4perl::Appender::Buffer;
###########################################

use strict;
use warnings;

our @ISA = qw(Log::Log4perl::Appender);

our $CVSVERSION   = '$Revision: 1.2 $';
our ($VERSION)    = ($CVSVERSION =~ /(\d+\.\d+)/);

###########################################
sub new {
###########################################
    my($class, %options) = @_;

    my $self = {
        appender=> undef,
        buffer  => [],
        options => { 
            max_messages  => undef, 
            trigger       => undef,
            trigger_level => undef,
        },
        level   => 0,
        %options,
    };

    if($self->{trigger_level}) {
        $self->{trigger} = level_trigger($self->{trigger_level});
    }

        # Pass back the appender to be synchronized as a dependency
        # to the configuration file parser
    push @{$options{l4p_depends_on}}, $self->{appender};

        # Run our post_init method in the configurator after
        # all appenders have been defined to make sure the
        # appender we're playing 'dam' for really exists
    push @{$options{l4p_post_config_subs}}, sub { $self->post_init() };

    bless $self, $class;
}

###########################################
sub log {
###########################################
    my($self, %params) = @_;

    local $Log::Log4perl::caller_depth =
        $Log::Log4perl::caller_depth + 2;

        # Do we need to discard a message because there's already
        # max_size messages in the buffer?
    if(defined $self->{max_messages} and
       @{$self->{buffer}} == $self->{max_messages}) {
        shift @{$self->{buffer}};
    }
        # Ask the appender to save a cached message in $cache
    $self->{app}->SUPER::log(\%params,
                         $params{log4p_category},
                         $params{log4p_level}, \my $cache);

        # Save it in the appender's message buffer, but only if
        # it hasn't been suppressed by an appender threshold
    if( defined $cache ) {
        push @{ $self->{buffer} }, $cache;
    }

    $self->flush() if $self->{trigger}->($self, \%params);
}

###########################################
sub flush {
###########################################
    my($self) = @_;

        # Flush pending messages if we have any
    for my $cache (@{$self->{buffer}}) {
        $self->{app}->SUPER::log_cached($cache);
    }

        # Empty buffer
    $self->{buffer} = [];
}

###########################################
sub post_init {
###########################################
    my($self) = @_;

    if(! exists $self->{appender}) {
       die "No appender defined for " . __PACKAGE__;
    }

    my $appenders = Log::Log4perl->appenders();
    my $appender = Log::Log4perl->appenders()->{$self->{appender}};

    if(! defined $appender) {
       die "Appender $self->{appender} not defined (yet) when " .
           __PACKAGE__ . " needed it";
    }

    $self->{app} = $appender;
}

###########################################
sub level_trigger {
###########################################
    my($level) = @_;

        # closure holding $level
    return sub {
        my($self, $params) = @_;

        return Log::Log4perl::Level::to_priority(
                 $params->{log4p_level}) >= 
               Log::Log4perl::Level::to_priority($level);
    };
}
    
###########################################
sub DESTROY {
###########################################
    my($self) = @_;
}

1;

__END__

=encoding utf8

=head1 NAME

    Log::Log4perl::Appender::Buffer - Buffering Appender

=head1 SYNOPSIS

    use Log::Log4perl qw(:easy);

    my $conf = qq(
    log4perl.category                  = DEBUG, Buffer

        # Regular Screen Appender
    log4perl.appender.Screen           = Log::Log4perl::Appender::Screen
    log4perl.appender.Screen.stdout    = 1
    log4perl.appender.Screen.layout    = PatternLayout
    log4perl.appender.Screen.layout.ConversionPattern = %d %p %c %m %n

        # Buffering appender, using the appender above as outlet
    log4perl.appender.Buffer               = Log::Log4perl::Appender::Buffer
    log4perl.appender.Buffer.appender      = Screen
    log4perl.appender.Buffer.trigger_level = ERROR
    );

    Log::Log4perl->init(\$conf);

    DEBUG("This message gets buffered.");
    INFO("This message gets buffered also.");

    # Time passes. Nothing happens. But then ...

    print "It's GO time!!!\n";

    ERROR("This message triggers a buffer flush.");

=head1 DESCRIPTION

C<Log::Log4perl::Appender::Buffer> takes these arguments:

=over 4

=item C<appender>

Specifies the name of the appender it buffers messages for. The
appender specified must be defined somewhere in the configuration file,
not necessarily before the definition of 
C<Log::Log4perl::Appender::Buffer>.

=item C<max_messages>

Specifies the maximum number of messages the appender will hold in
its ring buffer. C<max_messages> is optional. By default,
C<Log::Log4perl::Appender::Buffer> will I<not> limit the number of
messages buffered. This might be undesirable in long-running processes
accumulating lots of messages before a flush happens. If
C<max_messages> is set to a numeric value,
C<Log::Log4perl::Appender::Buffer> will displace old messages in its
buffer to make room if the buffer is full.

=item C<trigger_level>

If trigger_level is set to one of Log4perl's levels (see
Log::Log4perl::Level), a C<trigger> function will be defined internally
to flush the buffer if a message with a priority of $level or higher
comes along. This is just a convenience function. Defining

    log4perl.appender.Buffer.trigger_level = ERROR

is equivalent to creating a trigger function like

    log4perl.appender.Buffer.trigger = sub {   \
        my($self, $params) = @_;               \
        return $params->{log4p_level} >=       \
               $Log::Log4perl::Level::ERROR; }

See the next section for defining generic trigger functions.

=item C<trigger>

C<trigger> holds a reference to a subroutine, which
C<Log::Log4perl::Appender::Buffer> will call on every incoming message
with the same parameters as the appender's C<log()> method:

        my($self, $params) = @_;

C<$params> references a hash containing
the message priority (key C<l4p_level>), the
message category (key C<l4p_category>) and the content of the message
(key C<message>).

If the subroutine returns 1, it will trigger a flush of buffered messages.

Shortcut 

=back

=head1 DEVELOPMENT NOTES

C<Log::Log4perl::Appender::Buffer> is a I<composite> appender.
Unlike other appenders, it doesn't log any messages, it just
passes them on to its attached sub-appender.
For this reason, it doesn't need a layout (contrary to regular appenders).
If it defines none, messages are passed on unaltered.

Custom filters are also applied to the composite appender only.
They are I<not> applied to the sub-appender. Same applies to appender
thresholds. This behaviour might change in the future.

=head1 LICENSE

Copyright 2002-2013 by Mike Schilli E<lt>m@perlmeister.comE<gt> 
and Kevin Goess E<lt>cpan@goess.orgE<gt>.

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

=head1 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.