On 14 June 2013 17:35, Christopher Schultz <ch...@christopherschultz.net> wrote: > Mark, > > On 6/14/13 12:21 PM, Mark Thomas wrote: >> On 14/06/2013 16:57, Christopher Schultz wrote: >>> Mark, >>> >>> On 6/14/13 3:16 AM, Mark Thomas wrote: >>>> On 14/06/2013 03:31, Christopher Schultz wrote: >>>> >>>>> It might be nice if this were not a one-of-many decision, but if a >>>>> client could choose more than one type. A bit-mask or a list of >>>>> scan-types would be nice. I could see the same type of scanner being >>>>> used for multiple different purposes. >>>> >>>> That is what ServletContainerIniiializers are for. >>> >>> Well, crap. I had never seen those before. >>> >>> I'm curious, though. Thinking about this the other day with a colleague >>> who was complaining about some kind of Spring configuration that >>> evidently loaded every class available on the classpath and kept them in >>> memory (thus leading to heap and PermGen issues), I concluded that the >>> only sane way to do this kind of probing would be to probe everything in >>> a ClassLoader that was intended to be discarded after the probing as to >>> avoid loading classes unnecessarily. >>> >>> If an SCI retains a reference to any of the Class objects in the >>> Set<Class> parameter, that hypothetical throw-away ClassLoader is no >>> longer thrown-away. >> >> The early Tomcat 7 implementations did it like this - loaded every class >> and then examined the class object. More recent implementations use BCEL >> to look at the byte code. It is faster and uses less memory. We also use >> caching to ensure each class is only processed once.
That functionality sounds like it might be useful as a general purpose library item, possibly as part of a utility jar for Commons BCEL. For example JMeter has to scan classes for certain interfaces on startup. It's current implementation is a bit wasteful. > Cool. What Classloader gets used to actually load the Class objects, > though? BCEL reads class files as files. http://commons.apache.org/proper/commons-bcel/ > In the pathological case of @HandlesType('java.lang.Object') > that means everything gets loaded into .. the WebappClassLoader? > > One could imagine a case where an SCI wants to look at everything, but > then only ends up caring about 2% of what's been loaded. Is that just > the price you have to pay for inspecting everything -- that you > seriously waste PermGen? (at least for current Oracle JVMs) > > -chris > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For additional commands, e-mail: dev-h...@tomcat.apache.org
