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

       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.

perl v5.36.0                                       2022-10-30                        Appender::Synchronized(3pm)

       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@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.

   Performancetips
       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.

   Advancedconfiguration
       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.

   SemaphoreuserandgroupIDswithmod_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.

       "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.

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

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

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

           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.");