Affects Version/s: None
Fix Version/s: 2.0-beta5
(update 2013 Feb 4: changed summary.
Previous title: Add a method to the Layout interface to allow Loggers to discover if any of their Appenders need the location StackTraceElement.)
Use Case: any asynchronous Logger or Appender has this problem:
should it take a snapshot of the call stack (as implemented in Log4jLogEvent.getSource) or not?
This is an expensive method (1600+ nanoseconds on a machine with 2.9GHz cores) so you only want to call it if you need it. Currently there is no way to discover if the location information is used by any of the configured layouts.
If the Layout interface has a method that indicates whether the layout calls the LogEvent.getSource method, then the Logger can query its LoggerConfig if any of the configured Appenders has a Layout which needs location info. (Maybe boolean needsLocationInfo() would be a good name?)
With this information, a Logger can construct Log4jLogEvents with a non-null dummy StackTraceElement location if none of the layouts downstream need location info. The non-null dummy location would prevent LogEvent.getSource from taking a call stack snapshot.
The current AsynchAppender class would get an immediate performance boost from this, and custom asynchronous Loggers or Appenders would reap the same benefits.