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https://issues.apache.org/jira/browse/LOG4J2-3447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17512247#comment-17512247
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Piotr Karwasz commented on LOG4J2-3447:
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Hello [~PoojaTheCoder],
Thanks for bringing this to our attention. The Log4j 1.x bridge classes don't
contain any synchronized methods, because either they are no-ops or
synchronization is performed in native Log4j2 components.
However, we *did* miss the case of users, like you, that use custom Log4j 1.x
loggers. It will be fixed in the next release. In the mean time you can work
around the problem by adding synchronization to the {{append}} method of your
custom appender.
For the methods you cite check LOG4J2-3440: right now they are almost no-ops
(they add and remove appenders that are ignored by the logging system). I'll
take your remark into account, when working on that issue.
> Log4j 1.x 2.17.2 bridge - Synchronization issue in multithreading (Losing
> huge data in multithreading)
> ------------------------------------------------------------------------------------------------------
>
> Key: LOG4J2-3447
> URL: https://issues.apache.org/jira/browse/LOG4J2-3447
> Project: Log4j 2
> Issue Type: Bug
> Components: Log4j 1.2 bridge
> Affects Versions: 2.17.2
> Reporter: Pooja Pandey
> Assignee: Piotr Karwasz
> Priority: Major
> Fix For: 2.17.3
>
> Attachments: JavaLoggingMultiThTest.txt
>
>
> In our application we have migrated from log4j1.x to log4j1.x 2.17.2 bridge.
> With Log4j1.x there was no issue with multithreading but with log4j 1.x
> bridge we have noticed that in multithreading environment there is a huge
> data loss while logging, however single thread works fine. I see that in
> Category.java which Logger extends; many methods are not synchronized any
> more in log4j1.x bridge however which were synchronized in case of log4j1.x.
> I suspect this could be root causes of this multithreading problem.
> So as per my understanding synchronized class Category.java in the log4j1.x
> has become unsynchronized in log4j1.x 2.17.2 bridge. I am not sure if I am
> missing something.
> We wanted to know how to achieve successful multithreading logging using
> log4j 1.x 2.17.2 bridge.
> For reference, few methods which were synchronized earlier in log4j1.x but
> not anymore in log4j1.x bridge.
> # public void addAppender(final Appender appender)
> # public Appender getAppender(final String name)
> # public void removeAppender(final Appender appender)
> # public void removeAllAppenders()
> # In log4j 1.x bridge following method is used for logging which doesn't
> look like synchronized. -> void maybeLog(final String fqcn, final
> org.apache.logging.log4j.Level level, final Object message, final Throwable
> throwable); However in log4j1.x following method was used which looks like
> synchronized. -> void forcedLog(String fqcn, Priority level, Object message,
> Throwable t) -> void callAppenders(LoggingEvent event), where method void
> callAppenders(LoggingEvent event) looks snychronized.
>
> I am attaching sample test program as well which I have used to test
> multithreading logging in my application. (Please Note that in this test
> program, class CustomLogger is a dummy class, which you would need to replace
> with your logger). We are using Custom Rolling Appender in our application
> and following is the content of log4j properties file.
> [^JavaLoggingMultiThTest.txt]
> #Custom Rolling Appender
> log4j.appender.R=test.CustomMultiProcessRollingAppender
> log4j.appender.R.File=${user.home}/log4j-multithreading-test.log
> log4j.appender.R.RollOverOnStartup=true
> log4j.appender.R.RollOverOnSize=false
> log4j.appender.R.RollOverMaxFileSize=100MB
> log4j.appender.R.RollOverMaxBackupIndex=10
> log4j.appender.R.RollOverOnPeriodic=false
> log4j.appender.R.RollOverPeriodicStartDate=
> log4j.appender.R.RollOverPeriodicFrequency=1
> log4j.appender.R.layout=org.apache.log4j.PatternLayout
> log4j.appender.R.layout.ConversionPattern=%d %-8M [%t] - %m%n
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