man Log::Log4perl::Appender::Buffer () - Buffering Appender


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


    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


    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.");


CWLog::Log4perl::Appender::Buffer takes these arguments: 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 CWLog::Log4perl::Appender::Buffer. Specifies the maximum number of messages the appender will hold in its ring buffer. CWmax_messages is optional. By default, CWLog::Log4perl::Appender::Buffer will not limit the number of messages buffered. This might be undesirable in long-running processes accumulating lots of messages before a flush happens. If CWmax_messages is set to a numeric value, CWLog::Log4perl::Appender::Buffer will displace old messages in its buffer to make room if the buffer is full. If trigger_level is set to one of Log4perl's levels (see Log::Log4perl::Level), a CWtrigger function will be defined internally to flush the buffer if a message with a priority of CW$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} >=       \
               $Log::Log4perl::Level::ERROR; }
See the next section for defining generic trigger functions. CWtrigger holds a reference to a subroutine, which CWLog::Log4perl::Appender::Buffer will call on every incoming message with the same parameters as the appender's CWlog() method:
        my($self, $params) = @_;
CW$params references a hash containing the message priority (key CWl4p_level), the message category (key CWl4p_category) and the content of the message (key CWmessage). If the subroutine returns 1, it will trigger a flush of buffered messages. Shortcut


CWLog::Log4perl::Appender::Buffer is a 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 not applied to the sub-appender. Same applies to appender thresholds. This behaviour might change in the future.


Copyright 2004 by Mike Schilli, all rights reserved. This program is free software, you can redistribute it and/or modify it under the same terms as Perl itself.


2004, Mike Schilli <>