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From Joern Huxhorn <jhuxh...@googlemail.com>
Subject Re: log4j2 parameterized msg with throwable
Date Mon, 19 Sep 2011 22:19:59 GMT

On 19.09.2011, at 22:09, ralph.goers @dslextreme.com wrote:

> On Mon, Sep 19, 2011 at 1:07 PM, ralph.goers @dslextreme.com <ralph.goers@dslextreme.com>
> On Mon, Sep 19, 2011 at 10:07 AM, John Vasileff <john.lists@gmail.com> wrote:
> What do you think about an optional LazyRenderMessage interface (I'm sure there is a
better name for this) that could be used by Message types that have expensive constructers?
> interface LazyRenderMessage {
>   void render();
> }
> The logger would call render() immediately after checking isEnabled for level and marker.
 So, this should not affect serialization - the object will either be fully constructed or
discarded right away.
> This would allow ThreadDumpMessage Thread.getAllStackTraces() work to be avoided unless
logging will actually occur (or is likely to occur in the case of complex filters).
> The benefit of course is that trace(THREAD_DUMP_MARKER, new ThreadDumpMessage()) could
be left in production code without if isTraceEnabled(...) { ... }, and with very little overhead
- creating a short lived object that does nothing in the constructor is pretty cheap these
> This would also help for Message types like ParameterizedMessage to avoid parseArguments(arguments)
when they are created by application code.
> I see some merit in this idea. But you are right, it really needs a better name.
> One other point, though, is that there should always be a constructor that allows immediate
rendering. I could easily see the ThreadDumpMessage being used for other purposes and never
being passed to a logger. For example, I could create two ThreadDumpMessages at slightly different
points in time and then only print the differences between them.

But the whole idea of the Message interface was the lazy evaluation of the expensive String
creation with the suggestion to also cache those strings for reuse. Otherwise using toString()
wouldn't make a big difference...

Printing the differences between two ThreadDumpMessages would be an additional functionality,
of course. I guess that something like a populate() method filling in the stacktrace (separate
from string creation) would make sense. That could be called automatically if it wasn't called
explicitly before execution of getFormattedMessage()...

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