Niclas Hedhman created POLYGENE-277:
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Summary: Logging Extension SPI
Key: POLYGENE-277
URL: https://issues.apache.org/jira/browse/POLYGENE-277
Project: Polygene
Issue Type: New Feature
Reporter: Niclas Hedhman
(sent to [email protected] on 25 Nov 2017)
We have relatively little logging going on in the Core Runtime and also in most
libraries/extensions. Part of the reason is that there is not enough consensus
on what the best logging approach is, and the most used ones are all horrible.
I suggest that we introduce a Logging Extension SPI, and in good Polygene
tradition define our direct needs from top/down, and then allow for pluggable
extensions to deal with this as they see fit.
I think there is no need for a "LoggerFactory" (I could be wrong), but that we
simply introduce a few types to be injectable in @Structure scope, each
dedicated for the purpose, instead of the generic "log" that is prevalent in
logging systems deriving from Log4j. There are also control needs, as I prefer
to not have external configuration as the primary controller for what is used
or not, since that will effectively become implementation specific. Things like
log namespace and enable/disable must exist in the SPI, possibly other things.
And I think the extension of controls should also be a prescribed mechanism,
maybe have additional common configuration options in the SPI, even if they
don't apply to all implementations, e.g. Formatting which is very common, but
not for a log that writes entities.
I see 4 distinct subsystems within this SPI;
Trace - dealing with tracing of methods. Since we own the method
invocations, this will be relatively easy to do throughout a Polygene
application, and this injectable type is about controlling what is traced,
where reporting goes and what type of timing should be applied. Here is the
greatest level of integration into the Core Runtime.
In the library-logging, this is enabled in bootstrap, but I have since changed
my mind and think we need it to be controllable in runtime.
Debug - We all need debug information, and be able to let the code tell us
what is going on. The output is dedicated for developers, and is disabled in
Application.production mode. This is one of the most common use-cases,
especially for us developers. @Structure Debug debug; and reasonable methods on
that type is all we need. We should also try to use lambdas here, to get around
the if( debug.isEnabled() ){}, which is ugly and debug.debug( () -> "here!" +
param ); would look better and don't incur the cost of message construction if
not enabled.
LogBook - Better name might needed. The "Captain's Log" is all about the
information that production operations personnel is interested in. Important
state changes, events and other relevant information is to be communicated here.
Audit - Many business applications have Audit requirements. I think we
should have dedicated support for this, rather than expecting people to model
the whole infrastructure from scratch.
As usual, I think Polygene should provide all these things in much more
type-safe fashion and customizable types, than what we have in "traditional
logging" systems.
By making this an SPI, and by having Noop implementation(s) as default, it is
much easier for people to default to using this, rather than SLF4J, which
frankly is horrible (albeit prolific in the enterprise).
In the implementation side, there will be room for both traditional solutions
as well as innovation. Oh, yeah... We should try to figure out if we can
redirect the existing slf4j, log4j, jdk, commons-logging and what not APIs to
go through our SPI, to provide a unified channel for Polygene applications.
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