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From Gary Gregory <garydgreg...@gmail.com>
Subject RE: Proposed change to MarkerManager API
Date Mon, 07 Apr 2014 03:39:42 GMT
Before dealing with the complications of more than one parent, I think one concept mere mortals
should be able to deal with is being able to define a marker hierarchy the same way we can
define logger hierarchies with dot names. So I can say MarkerManger.getMarker("com.foo.bar.MyMarker").

Gary

Gary

-------- Original message --------
From: Bruce Brouwer <bruce.brouwer@gmail.com> 
Date:04/06/2014  22:35  (GMT-05:00) 
To: Log4J Developers List <log4j-dev@logging.apache.org> 
Subject: Proposed change to MarkerManager API 

I hate changing API as much as the next guy, but there is an API in MarkerManager that I think
could be improved. 

MarkerManager.getMarker(name) gets a marker, optionally creating it if it doesn't exist. I
support this with no change.

MarkerManager.getMarker(name, parents...) I have an issue with. It does not in all cases return
me a marker that has the parents specified. If the marker already existed, it is simply returned
with no changes made to the parents. I propose removing this method and replacing it with...

MarkerManager.define(name, parents...) This method will create the marker with the specified
parents if it does not exist. If it does exist, it will change the parent list to be the list
specified. 

Here's another reason I want to change this. Consider these two classes:

public class A {
  private final static Marker m = MarkerManager.getMarker("m", "p");
}

public class B {
  private final static Marker m = MarkerManager.getMarker("m");
}

If class A gets loaded first, marker "m" will have parent "p". But if class B gets loaded
first, then marker "m" will have no parents. I generally don't like relying on the exact order
that classes are loaded when the two classes aren't related. 

But if we consider my proposed change:

public class A {
  private final static Marker m = MarkerManager.define("m", "p");
}

public class B {
  private final static Marker m = MarkerManager.getMarker("m");
}

Now the behavior is the same, no matter which class is loaded first. It looks clearer to me
as the definition of the marker happens in one place, while class B is only interested in
a reference to a potentially already defined marker, but makes no statement about what parents
it has. 

I also don't like the idea of the define method throwing an exception if the marker already
exists or getMarker returning null if the marker doesn't exist; again for the reasons that
I don't want class loading order to impact behavior. 

I understand that if there are two statements defining a marker with different parents, whichever
one runs last is going to be the winner. It's not great if that happens, but I shouldn't be
defining a marker in two places. In reality, the best thing would be to make class B reference
the marker field in class A. If I do that, then the current implementation would work fine;
I'm just thinking of the case where somebody doesn't (or can't) do the best thing. Then, a
distinction between get and define could be helpful.

Does this sound like an acceptable change that we could get into log4j-api before GA?

-- 

Bruce Brouwer
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