Add logging interface and log callbacks

[wmiaw]

Define a logging interface and add log callbacks to the core code to provide insight into MSL logic.

Some requirements:

• Function entry/exit.
• Decision making.
• Error severities.
• Logging areas.

SLF4J (Simple Logging Facade for Java) was suggested but requires inclusion of a specific library/JAR (slf4j-api.jar) which can cause problems. It may serve as a useful design example.

There is a performance concern with always calling the log functions, and building their arguments, even if the log message will be discarded. An outer if statement is one way to address this.

[quidryan]

"inclusion of a specific library/JAR (slf4j-api.jar) which can cause problems" What problems would it create?

[wmiaw]

The issues we discussed in the last internal MSL Users Group meeting, particularly around dependencies and the impact if that specific library is no longer maintained or needs to be replaced by something else in a couple of years.