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Subject: Re: why AppenderSkeleton.doAppend is synchronized ?
From: Curt Arnold <carnold@apache.org>
In-Reply-To: <4B97CAB8.5050901@gmail.com>
Date: Wed, 10 Mar 2010 23:00:03 -0600
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References: <4B97CAB8.5050901@gmail.com>
To: "Log4J Users List" <log4j-user@logging.apache.org>


On Mar 10, 2010, at 10:37 AM, Stefano Nichele wrote:

> Hi all,
> looking for perfomance issue in my server application, I found that =
AppenderSkeleton.doAppend method is synchronized.
> I google a bit and I have found some messages but not a clear anwser =
to my doubt: why that method is synchronized ? it seems that just check =
the threshold, the filter and that "append" the event but in this way is =
serializing all log calls. I'm logging events on the db and also using =
AsyncAppender + my own appender I'm not able to obtain good performance =
since just one thread at time can append (insert) an event and the =
AsyncAppender queue grows pretty quick.
>=20
> For sure i'm missing something...could you help me to understand the =
root reason for having it synchronized ? I'm thinking to have my owm =
implementation of AppenderSkeleton removing synchronization but I'm not =
sure if there are drawbacks that im not taking in consideration.
>=20
> Thanks a lot in advance
> ste
>=20
>=20

log4j 1.2 was designed a long time ago and relies on that big lock to =
provide thread safety.  Other classes in log4j (layouts, appenders and =
the like) were designed assuming that they would be externally =
synchronized by that lock and likely not safe if that lock is bypassed.

You could either implement the Appender interface or extend =
AppenderSkeleton but override doAppend (copying and pasting the =
implementation but without the synchronized modifier, but all appenders, =
layouts, etc used must be able to operate safely without that lock.

Addressing this issue is one of the core design goals for log4j 2.0 =
(http://issues.apache.org/jira/browse/LOG4J2-3)=

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