1Appender::Synchronized(U3s)er Contributed Perl DocumentatAipopnender::Synchronized(3)
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NAME

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

9           use Log::Log4perl qw(:easy);
10
11           my $conf = qq(
12           log4perl.category                   = WARN, Syncer
13
14               # File appender (unsynchronized)
15           log4perl.appender.Logfile           = Log::Log4perl::Appender::File
16           log4perl.appender.Logfile.autoflush = 1
17           log4perl.appender.Logfile.filename  = test.log
18           log4perl.appender.Logfile.mode      = truncate
19           log4perl.appender.Logfile.layout    = SimpleLayout
20
21               # Synchronizing appender, using the file appender above
22           log4perl.appender.Syncer            = Log::Log4perl::Appender::Synchronized
23           log4perl.appender.Syncer.appender   = Logfile
24       );
25
26           Log::Log4perl->init(\$conf);
27           WARN("This message is guaranteed to be complete.");
28

DESCRIPTION

30       If multiple processes are using the same "Log::Log4perl" appender
31       without synchronization, overwrites might happen. A typical scenario
32       for this would be a process spawning children, each of which inherits
33       the parent's Log::Log4perl configuration.
34
35       In most cases, you won't need an external synchronisation tool like
36       Log::Log4perl::Appender::Synchronized at all. Log4perl's file appender,
37       Log::Log4perl::Appender::File, for example, provides the "syswrite"
38       mechanism for making sure that even long log lines won't interleave.
39       Short log lines won't interleave anyway, because the operating system
40       makes sure the line gets written before a task switch occurs.
41
42       In cases where you need additional synchronization, however, you can
43       use "Log::Log4perl::Appender::Synchronized" as a gateway between your
44       loggers and your appenders. An appender itself,
45       "Log::Log4perl::Appender::Synchronized" just takes two additional
46       arguments:
47
48       "appender"
49           Specifies the name of the appender it synchronizes access to. The
50           appender specified must be defined somewhere in the configuration
51           file, not necessarily before the definition of
52           "Log::Log4perl::Appender::Synchronized".
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54       "key"
55           This optional argument specifies the key for the semaphore that
56           "Log::Log4perl::Appender::Synchronized" uses internally to ensure
57           atomic operations. It defaults to "_l4p". If you define more than
58           one "Log::Log4perl::Appender::Synchronized" appender, it is
59           important to specify different keys for them, as otherwise every
60           new "Log::Log4perl::Appender::Synchronized" appender will nuke
61           previously defined semaphores. The maximum key length is four
62           characters, longer keys will be truncated to 4 characters --
63           "mylongkey1" and "mylongkey2" are interpreted to be the same:
64           "mylo" (thanks to David Viner <dviner@yahoo-inc.com> for pointing
65           this out).
66
67       "Log::Log4perl::Appender::Synchronized" uses
68       Log::Log4perl::Util::Semaphore internally to perform locking with
69       semaphores provided by the operating system used.
70
71   Performance tips
72       The "Log::Log4perl::Appender::Synchronized" serializes access to a
73       protected resource globally, slowing down actions otherwise performed
74       in parallel.
75
76       Unless specified otherwise, all instances of
77       "Log::Log4perl::Appender::Synchronized" objects in the system will use
78       the same global IPC key "_l4p".
79
80       To control access to different appender instances, it often makes sense
81       to define different keys for different synchronizing appenders. In this
82       way, Log::Log4perl serializes access to each appender instance
83       separately:
84
85           log4perl.category                   = WARN, Syncer1, Syncer2
86
87               # File appender 1 (unsynchronized)
88           log4perl.appender.Logfile1           = Log::Log4perl::Appender::File
89           log4perl.appender.Logfile1.filename  = test1.log
90           log4perl.appender.Logfile1.layout    = SimpleLayout
91
92               # File appender 2 (unsynchronized)
93           log4perl.appender.Logfile2           = Log::Log4perl::Appender::File
94           log4perl.appender.Logfile2.filename  = test2.log
95           log4perl.appender.Logfile2.layout    = SimpleLayout
96
97               # Synchronizing appender, using the file appender above
98           log4perl.appender.Syncer1            = Log::Log4perl::Appender::Synchronized
99           log4perl.appender.Syncer1.appender   = Logfile1
100           log4perl.appender.Syncer1.key        = l4p1
101
102               # Synchronizing appender, using the file appender above
103           log4perl.appender.Syncer2            = Log::Log4perl::Appender::Synchronized
104           log4perl.appender.Syncer2.appender   = Logfile2
105           log4perl.appender.Syncer2.key        = l4p2
106
107       Without the ".key = l4p1" and ".key = l4p2" lines, both Synchronized
108       appenders would be using the default "_l4p" key, causing unnecessary
109       serialization of output written to different files.
110
111   Advanced configuration
112       To configure the underlying Log::Log4perl::Util::Semaphore module in a
113       different way than with the default settings provided by
114       Log::Log4perl::Appender::Synchronized, use the following parameters:
115
116           log4perl.appender.Syncer1.destroy  = 1
117           log4perl.appender.Syncer1.mode     = sub { 0775 }
118           log4perl.appender.Syncer1.uid      = hugo
119           log4perl.appender.Syncer1.gid      = 100
120
121       Valid options are "destroy" (Remove the semaphore on exit), "mode"
122       (permissions on the semaphore), "uid" (uid or user name the semaphore
123       is owned by), and "gid" (group id the semaphore is owned by),
124
125       Note that "mode" is usually given in octal and therefore needs to be
126       specified as a perl sub {}, unless you want to calculate what 0755
127       means in decimal.
128
129       Changing ownership or group settings for a semaphore will obviously
130       only work if the current user ID owns the semaphore already or if the
131       current user is "root". The "destroy" option causes the current process
132       to destroy the semaphore on exit. Spawned children of the process won't
133       inherit this behavior.
134
135   Semaphore user and group IDs with mod_perl
136       Setting user and group IDs is especially important when the
137       Synchronized appender is used with mod_perl. If Log4perl gets
138       initialized by a startup handler, which runs as root, and not as the
139       user who will later use the semaphore, the settings for uid, gid, and
140       mode can help establish matching semaphore ownership and access rights.
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DEVELOPMENT NOTES

143       "Log::Log4perl::Appender::Synchronized" is a composite appender.
144       Unlike other appenders, it doesn't log any messages, it just passes
145       them on to its attached sub-appender.  For this reason, it doesn't need
146       a layout (contrary to regular appenders).  If it defines none, messages
147       are passed on unaltered.
148
149       Custom filters are also applied to the composite appender only.  They
150       are not applied to the sub-appender. Same applies to appender
151       thresholds. This behaviour might change in the future.
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LICENSE

154       Copyright 2002-2013 by Mike Schilli <m@perlmeister.com> and Kevin Goess
155       <cpan@goess.org>.
156
157       This library is free software; you can redistribute it and/or modify it
158       under the same terms as Perl itself.
159

AUTHOR

161       Please contribute patches to the project on Github:
162
163           http://github.com/mschilli/log4perl
164
165       Send bug reports or requests for enhancements to the authors via our
166
167       MAILING LIST (questions, bug reports, suggestions/patches):
168       log4perl-devel@lists.sourceforge.net
169
170       Authors (please contact them via the list above, not directly): Mike
171       Schilli <m@perlmeister.com>, Kevin Goess <cpan@goess.org>
172
173       Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens
174       Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse
175       Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis
176       Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier  David
177       Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter,
178       Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars
179       Thegler, David Viner, Mac Yang.
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183perl v5.36.0                      2022-10-24         Appender::Synchronized(3)
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