Re: Interesting deadlock situations - org.apache.log4j.spi.RootCategory

[Ceki Gülcü <ce...@qos.ch>]

This issue did never came up until a few days ago. I had a long discussion 
with Erik Meade on irc on quite a similar problem. 
(irc://irc.freenode.org:6667 on channel #apache-log4j)

At 02:17 PM 10/24/2003 -0700, Elias Ross wrote:

>I just came across a deadlock condition in my code brought out by
>Log4J.  Here is a simplified view of the objects in play:
>
>class State {
>    Logger log1;
>
>    synchronized void setState() {
>      // Something takes a long time here
>      log.debug("hello world");
>    }
>
>    synchronized Object getState() {
>    }
>
>    public String toString() {
>       return "state=" + getState();
>    }
>}
>
>So, imagine that I call in thread (1)
>
>Logger log2;
>State s = new State();
>log.debug(s);
>
>And then, in another thread (2), I called setState().  It is in the
>middle of setState when this debug statement is fired.
>
>In thread (1), the logger holds a lock on
>'org.apache.log4j.spi.RootCategory'.  The renderer attempts construct
>the message by calling s.toString(), and toString calls getState().
>
>Thread (1) has to wait for setState in thread (2) to exit.  But setState
>can't exit until it has finished logging.
>
>So, I am wondering why can't the rendered render without holding the
>lock on 'org.apache.log4j.spi.RootCategory'?
>
>(An obvious fix is to not lock the getState routine.)
>
>
>Maybe the moral of the story is don't have your debug statements hold
>locks on your objects.
>
>
>
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-- 
Ceki Gülcü

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