Can you look at rewriteappender and rewritepolicy will fit in?
Ability to modify the event message and add properties and possibly
anything else via configuration.
On Sep 23, 2011, at 12:37 AM, Ralph Goers <ralph.go...@dslextreme.com>
wrote:
On Sep 22, 2011, at 10:16 PM, Curt Arnold wrote:
Been lurking and watching the thread, wanted to throw some comments
out without fully following the thread. Take everything with a
grain of salt.
Why? Your input is just as valuable as everyone else's.
log4j 1.2's AsyncAppender does a bit of this by calling all sorts
of methods to force the lazy initialization of the event prior to
the event being queued for processing by the worker thread. This
can result in a lot of unnecessary work on the calling thread
copying things like the MDC that might but might not be used in the
eventual message formatting.
For some reason I haven't gotten around to the AsyncAppender. I'm
afraid some copying of data when generating the LogEvent is
inevitable.
Performing the rendering of the message on the calling thread is
also not desirable since things like formatting floating point
numbers can be surprisingly expensive.
One advantage of the Message interface is that it can provide
information that can help determine when it should be rendered. For
example, in addition to the initialize method John proposed for the
DeferredMessage it could also indicate when it should be deferred
to. Of course, Messages never need to format themselves until
getFormattedMessage is called.
In some of my earlier design experiments, I was very fond of having
the formatter/layout object supporting a two phase approach where
the layout had an opportunity to "extract" from the logging event
on the calling thread and then process the extracted information
later on the worker thread. The extraction method would be
responsible to assemble the information that it needed into an
arbitrary immutable object that would be passed blindly by the
framework to the formatting phase at the proper time. The
implementation had the choice of whether it wanted to render all
the way to String on the calling thread (say if it were cheap) on
do the minimum to get immutable objects in the calling thread and
do all the heavy lifting on the worker thread.
I'm not sure I see the benefit of creating another object. You still
need the LogEvent. Most of the work to insure the LogEvent can be
passed to another thread really needs to be done anyway. Currently
the constructor copies the MDC and NDC and a ThrowableProxy is
constructed if a Throwable is present. About the only things that
aren't being done then is the setting of the caller's
StackTraceElement and setting the name of the current thread. It is
a simple matter to have the AsyncAppender cause those to be set.
FWIW, the LogEvent should be immutable from the perspective of
anything using it. Since LogEvent is an interface and only exposes
get methods this would be true, except that getContextMap and
getContextStack don't say they return unmodifiable objects and they
implementation isn't returning immutable objects. They should.
Without getting the layout participating, you almost will be doing
unnecessary work on the calling thread.
I don't necessarily disagree with this part. For example, the
Converters that deal with the caller's location could call
LogEvent.getSource during the first call to make sure the required
information in the LogEvent is captured. Of course, they would call
that same method during the rendering but that second call would be
very inexpensive.
I fleshed this approach out several years ago at https://svn.apache.org/repos/asf/logging/sandbox/experimental/pattern-layout
if anyone wants to take a look for ideas.
I'll take a look at this.
Ralph
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