phpman > man > Log::Log4perl::Appender::Synchronized

NAME
    Log::Log4perl::Appender::Synchronized - Synchronizing other appenders

SYNOPSIS
        use Log::Log4perl qw(:easy);

        my $conf = qq(
        log4perl.category                   = WARN, Syncer

            # File appender (unsynchronized)
        log4perl.appender.Logfile           = Log::Log4perl::Appender::File
        log4perl.appender.Logfile.autoflush = 1
        log4perl.appender.Logfile.filename  = test.log
        log4perl.appender.Logfile.mode      = truncate
        log4perl.appender.Logfile.layout    = SimpleLayout

            # Synchronizing appender, using the file appender above
        log4perl.appender.Syncer            = Log::Log4perl::Appender::Synchronized
        log4perl.appender.Syncer.appender   = Logfile
    );

        Log::Log4perl->init(\$conf);
        WARN("This message is guaranteed to be complete.");

DESCRIPTION
    If multiple processes are using the same "Log::Log4perl" appender without synchronization,
    overwrites might happen. A typical scenario for this would be a process spawning children, each
    of which inherits the parent's Log::Log4perl configuration.

    In most cases, you won't need an external synchronisation tool like
    Log::Log4perl::Appender::Synchronized at all. Log4perl's file appender,
    Log::Log4perl::Appender::File, for example, provides the "syswrite" mechanism for making sure
    that even long log lines won't interleave. Short log lines won't interleave anyway, because the
    operating system makes sure the line gets written before a task switch occurs.

    In cases where you need additional synchronization, however, you can use
    "Log::Log4perl::Appender::Synchronized" as a gateway between your loggers and your appenders. An
    appender itself, "Log::Log4perl::Appender::Synchronized" just takes two additional arguments:

    "appender"
        Specifies the name of the appender it synchronizes access to. The appender specified must be
        defined somewhere in the configuration file, not necessarily before the definition of
        "Log::Log4perl::Appender::Synchronized".

    "key"
        This optional argument specifies the key for the semaphore that
        "Log::Log4perl::Appender::Synchronized" uses internally to ensure atomic operations. It
        defaults to "_l4p". If you define more than one "Log::Log4perl::Appender::Synchronized"
        appender, it is important to specify different keys for them, as otherwise every new
        "Log::Log4perl::Appender::Synchronized" appender will nuke previously defined semaphores.
        The maximum key length is four characters, longer keys will be truncated to 4 characters --
        "mylongkey1" and "mylongkey2" are interpreted to be the same: "mylo" (thanks to David Viner
        <dviner AT yahoo-inc.com> for pointing this out).

    "Log::Log4perl::Appender::Synchronized" uses Log::Log4perl::Util::Semaphore internally to
    perform locking with semaphores provided by the operating system used.

  Performance tips
    The "Log::Log4perl::Appender::Synchronized" serializes access to a protected resource globally,
    slowing down actions otherwise performed in parallel.

    Unless specified otherwise, all instances of "Log::Log4perl::Appender::Synchronized" objects in
    the system will use the same global IPC key "_l4p".

    To control access to different appender instances, it often makes sense to define different keys
    for different synchronizing appenders. In this way, Log::Log4perl serializes access to each
    appender instance separately:

        log4perl.category                   = WARN, Syncer1, Syncer2

            # File appender 1 (unsynchronized)
        log4perl.appender.Logfile1           = Log::Log4perl::Appender::File
        log4perl.appender.Logfile1.filename  = test1.log
        log4perl.appender.Logfile1.layout    = SimpleLayout

            # File appender 2 (unsynchronized)
        log4perl.appender.Logfile2           = Log::Log4perl::Appender::File
        log4perl.appender.Logfile2.filename  = test2.log
        log4perl.appender.Logfile2.layout    = SimpleLayout

            # Synchronizing appender, using the file appender above
        log4perl.appender.Syncer1            = Log::Log4perl::Appender::Synchronized
        log4perl.appender.Syncer1.appender   = Logfile1
        log4perl.appender.Syncer1.key        = l4p1

            # Synchronizing appender, using the file appender above
        log4perl.appender.Syncer2            = Log::Log4perl::Appender::Synchronized
        log4perl.appender.Syncer2.appender   = Logfile2
        log4perl.appender.Syncer2.key        = l4p2

    Without the ".key = l4p1" and ".key = l4p2" lines, both Synchronized appenders would be using
    the default "_l4p" key, causing unnecessary serialization of output written to different files.

  Advanced configuration
    To configure the underlying Log::Log4perl::Util::Semaphore module in a different way than with
    the default settings provided by Log::Log4perl::Appender::Synchronized, use the following
    parameters:

        log4perl.appender.Syncer1.destroy  = 1
        log4perl.appender.Syncer1.mode     = sub { 0775 }
        log4perl.appender.Syncer1.uid      = hugo
        log4perl.appender.Syncer1.gid      = 100

    Valid options are "destroy" (Remove the semaphore on exit), "mode" (permissions on the
    semaphore), "uid" (uid or user name the semaphore is owned by), and "gid" (group id the
    semaphore is owned by),

    Note that "mode" is usually given in octal and therefore needs to be specified as a perl sub {},
    unless you want to calculate what 0755 means in decimal.

    Changing ownership or group settings for a semaphore will obviously only work if the current
    user ID owns the semaphore already or if the current user is "root". The "destroy" option causes
    the current process to destroy the semaphore on exit. Spawned children of the process won't
    inherit this behavior.

  Semaphore user and group IDs with mod_perl
    Setting user and group IDs is especially important when the Synchronized appender is used with
    mod_perl. If Log4perl gets initialized by a startup handler, which runs as root, and not as the
    user who will later use the semaphore, the settings for uid, gid, and mode can help establish
    matching semaphore ownership and access rights.

DEVELOPMENT NOTES
    "Log::Log4perl::Appender::Synchronized" 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.

LICENSE
    Copyright 2002-2013 by Mike Schilli <m AT perlmeister.com> and Kevin Goess <cpan AT goess.org>.

    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 AT lists.net

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