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From "Bruce Brouwer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-585) Markers not as powerful as slf4j
Date Sun, 06 Apr 2014 23:18:14 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13961566#comment-13961566

Bruce Brouwer commented on LOG4J2-585:

So, here are my thoughts. Maybe some of these should be made into new JIRAs.
* Are we ok with getMarker sometimes creating a marker with the specified parents and sometimes
returning a marker with a potentially different parent hierarchy? This is why my concept renamed
those methods to define(name, parents...). 
* Do we want a version of getMarker (or define) that takes a list of parent marker names,
in addition to the new one that takes a list of marker instances?
* Should it be ok to add a parent twice in the hierarchy, once as a grand parent, once as
a parent? If I was allowed to add marker X as an immediate parent of Y when X already existed
as a grandparent, then removing the X grandparent would allow marker Y to remain an instance
of X. The current implementation would not allow me to add X as a parent of Y and thus removing
grandparent X would make Y no longer an instance of X, even though I explicitly specified
I wanted X to be an immediate parent of Y. (This one is pretty minor and I'm willing to accept
what is done)
* Log4jMarker.getParents() should return a copy of the array so I can't change the contents
from outside the control of log4j
* Would a switch statement in Log4jMarker.isInstanceOf provide better performance, so there
aren't multiple length checks?
* slf4j-impl Log4jMarker is still backwards, treating parents as children and children as
parents. My concept code showed how I took care of this. In most cases, there is no real performance
* In slf4j-impl Log4jMarkerFactory.getDetachedMarker(), my impression was that it should create
a marker that wasn't actually attached yet to log4j, but by adding it as a child to a parent
that is attached would then make it attached. This implementation essentially creates the
slf4j marker as already attached.

> Markers not as powerful as slf4j
> --------------------------------
>                 Key: LOG4J2-585
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-585
>             Project: Log4j 2
>          Issue Type: Improvement
>          Components: API
>    Affects Versions: 2.0-rc1
>            Reporter: Bruce Brouwer
>         Attachments: ConceptMarkerBenchmark.java, CurrentMarkerBenchmark.java, log4j2-585-concept.patch
> Log4J's markers are not as flexible as markers in SLF4J. 
> First, SLF4J's markers are mutable. By allowing markers to be mutable, I can change the
relationship of markers to each other based upon runtime or business conditions. 
> Second, and more importantly I think, is that essentially SLF4J markers have this parent/child
relationship, much like Log4J, except that in SLF4J, I can essentially have a marker with
multiple parents. For example, I might want this structure:
> * Animal
> ** Bird
> *** Duck
> ** Mammal
> *** Bear
> *** Dolphin
> * Travels by
> ** Water
> *** Duck
> *** Dolphin
> ** Land
> *** Duck
> *** Bear
> ** Air
> *** Duck
> Of course, this is a contrived example, but I wanted to describe the relationships. Now,
if I wanted to filter based on markers that travel by Water for some appenders, and another
appender wants to filter by Mammals, I can't simply use the single marker of Dolphin. 
> Either we need to reverse the marker relationship so that it contains its children, much
like SLF4J, or we allow markers to have multiple parents, which I prefer because it could
make it more succinct to define:
> {code}
> private static final Marker BY_LAND = MarkerManager.getMarker("BY_LAND");
> private static final Marker BY_WATER = MarkerManager.getMarker("BY_WATER");
> private static final Marker DUCK = MarkerManager.getMarker("DUCK", BY_LAND, BY_WATER);
> {code}
> As for the Marker API, we would either need to change getParent to getParents, or get
rid of the getParent method from the API and just rely on the isInstanceOf method to handle
checking multiple parents by looking at private member variables (my preference)

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