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From Curt Arnold <carn...@apache.org>
Subject Re: svn commit: r439177 - in /logging/log4j/trunk/src/java/org/apache/log4j: scheduler/Scheduler.java spi/LocationInfo.java
Date Fri, 01 Sep 2006 16:18:29 GMT

On Sep 1, 2006, at 9:50 AM, Claudio Corsi wrote:

> Curt,
>
> I've read that using notifyAll compared to notify causes a  
> performance degradation. Have you run any performance tests  
> comparing this change?
>
> --Claudio

I did not do any performance tests on the change.  The change is in  
the Scheduler class which was developed for use by the configuration  
file monitors that would reconfigure log4j when a change in the  
configuration file is detected.  In this case, correctness is much  
more important than performance.  The scheduler has been observed to  
fail tests on Gump and the use of notify() when notifyAll() is needed  
might have been responsible.  I was hoping that the change would  
clean up the Gump failures but it appears that it has not.

 From section 3.2.4 (pg 192) of "Concurrent Programming in Java,  
Second Edition":
>
> In open, extensible designs, the conditions under which notify  
> apply are rather special and fragile.  The use of notify, and  
> optimizations of guarded conditions more generally, are common  
> sources of error.  As a general design tactic, it is a better idea  
> to isolate uses of notify to concurrency control utility classes  
> that can be heavily optimized and carefully reviewed and tested.

Getting something like org.apache.log4j.Scheduler done right is  
hard.   If we were targeting JDK 1.5, it would be a obvious to drop  
that class and use java.util.concurrent.ScheduledExecutorServer.  If  
we were to press on with log4j 1.3 and in light of the on-going test  
failures on Gump, we would need to consider either rolling back  
FileWatchdog to the log4j 1.2 implementation or take a hard look at  
org.apache.log4j.Scheduler.

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