As I see it, the problem is that at least some of the users seem to be
expecting Log4j to magically know when to call clear. It can't. The application
has to do it.
All the MDC is is a ThreadLocal where each Thread has its own Map associated
with the ThreadLocal. You can get and put all you want. In a webapp, of course,
if you add stuff to the MDC at the beginning of a request then you need to
remove it all at the end of the request. The normal pattern is
MDC.put(key, value);
try {
call servlet
} finally {
MDC.remove(key);
}
The problem with this is that it still leaves an empty Map in the ThreadLocal.
So when remove() removes the last element from the Map then the Map is removed
from the ThreadLocal.
FWIW, Logback suffered a similar issue in
http://jira.qos.ch/browse/LBCLASSIC-183.
Ralph
On May 29, 2012, at 10:31 PM, Christian Grobmeier wrote:
> Bringing this to the mailinglist.
>
> Ralph, I understand what you explained below, but I am lost on how to
> fix it. Do you have any more suggestions?
> I must actually admit that I am not familiar with MDC at all, probably
> that's my problem with it.
>
> On Wed, May 30, 2012 at 7:26 AM, <[email protected]> wrote:
>> https://issues.apache.org/bugzilla/show_bug.cgi?id=50486
>>
>> --- Comment #37 from Ralph Goers <[email protected]> ---
>> Yes, that is what clear is for.
>>
>> I don't see how Hierarchy.shutdown() can call MDC.clear(). Well, it could but
>> it would only clear the thread the shutdown is performed on which isn't
>> likely
>> to help much.
>>
>> Item 2 is likely to cause many problems. MDC.clear only clears the current
>> thread's ThreadLocal. Reinitializing the MDC will cause problems for all the
>> other threads.
>>
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>
>
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