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https://issues.apache.org/jira/browse/LOG4J2-585?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bruce Brouwer updated LOG4J2-585:
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Attachment: log4j2-585-concept.patch
Here is a log4j2-585-concept.patch that outlines my ideas for the Markers. It
is merely a concept and not intended to be committed yet. I'm sure I've
probably gone too far in some areas, but hear me out first.
For performance, I checked with JMH. So long as the marker hierarchy is no more
than 5 deep, the current Log4j code is faster, but after 5 deep, my concept is
faster than the current Log4j code. For the normal case of only one parent, the
current Log4j code can perform about 600,000 ops/ms, while my concept performs
about 200,000 ops/ms. A simpler version of my concept that did not include the
allParentNames variable was much slower, clocking in at only about 10,000
ops/ms.
The big driver behind my concept was to make Log4j Markers just as powerful as
slf4j. This means primarily two things: mutability and multiple parents.
First, I got rid of MarkerManager and turned Marker into a concrete, final
class. By making Marker an interface, clients might be inclined to implement
the interface themselves and cause issues because the parent hierarchy of their
markers would likely not match the parent hierarchy of Log4j's markers. It is
because of this that I don't like the idea of pluggable Marker factories.
Next, my ReadWriteLock is static. I did this to avoid creating a ton of lock
objects for each Marker. The majority of time, marker hierarchies are not
changing, so a lock that blocks most marker functions during an update is
likely not a concern. Furthermore, the most prevalent cases, such as calling
isInstanceOf, are not even guarded by a lock and allow ConcurrentHashMap to
provide all the performance possible.
getParents() is not a Set<Marker> instead of a simple Marker. This allows
multiple parents. I went with a custom Set implementation to be able to react
to changes to the parents set, which is used primarily to keep allParentNames
up to date.
The static methods that used to be on MarkerManager are not on Marker.
Marker.get works exactly like MarkerManager.getMarker. An overloaded version
allows you to indicate if you want a marker created if it does not exist. This
was necessary for use in the Slf4j-impl, but I could see it being valuable
elsewhere, too.
Marker.define works a little bit like MarkerManager.getMarker(name, parent),
but because Markers are not mutable, it ensures that the parents become the set
provided here. I like the name define better because it is clear to me that
this will make the marker look the way I just described. I did not like
MarkerManager.getMarker(name, parent) because it does not guarantee me that the
returned marker even has the specified parent. If the marker was created
earlier to this call, it won't have my specified parent.
Marker.undefine allows markers to be removed, which is a feature of slf4j and
it was fairly easy to support here.
So, is it worth a bit of a performance penalty to get all these features in
Markers?
> 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: 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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