Re: [aspectj-users] LTW and JRE classes

["Alexander Kriegisch" <alexander@xxxxxxxxxxxxxx>]

Sorry Andy, I forgot to mention the recursive invocation problem when
using the weaver as a system classloader. I tried to work around it by
putting everything on 'aj.class.path' which made the exception go away
but did not do anything with regard to aspect weaving.

-- 
Alexander Kriegisch
https://scrum-master.de


Andy Clement:

> Re: -Djava.system.class.loader=org.aspectj.weaver.loadtime.WeavingURLClassLoader
> 
> Been a while since I've tried that, I half expected that property not
> to work, but (on Java8) if I set it and I set aj.aspect.path then I
> see WeavingURLClassLoader kick in and try to work - it gets stuck in a
> recursive invocation problem though. Not sure what that is.
> 
> Caused by: java.lang.IllegalStateException: recursive invocation
> at java.lang.ClassLoader.initSystemClassLoader(ClassLoader.java:1443)
> at java.lang.ClassLoader.getSystemClassLoader(ClassLoader.java:1429)
> at java.util.ServiceLoader.loadInstalled(ServiceLoader.java:568)
> at java.util.ResourceBundle.<clinit>(ResourceBundle.java:376)
> at org.aspectj.weaver.WeaverMessages.<clinit>(WeaverMessages.java:19)
> at org.aspectj.weaver.bcel.ClassPathManager.addPath(ClassPathManager.java:103)
> 
> 
> Re: weaving java/javax
> 
> I think we've often said if you need to do that, do it offline and
> used a patched rt.jar/equivalent as it is more reliable. I can fully
> believe the JDK has moved on in terms of class loading mechanisms and
> AspectJ hasn't kept up.
> 
> 
> Alexander Kriegisch:
> 
>> One more question: What exactly is it good for to be able to replace the
>> system classloader by WeavingURLClassLoader via:
>> 
>> -Djava.system.class.loader=org.aspectj.weaver.loadtime.WeavingURLClassLoader
>> 
>> For me this does not do anything without an additional weaving agent
>> attached via '-javaagent:...'. Can you explain, maybe?
>> 
>> Source code reference:
>> https://github.com/eclipse/org.aspectj/blob/8c6b3ae13b105ce9bb9559de0ee4752cab5ba81c/loadtime/src/org/aspectj/weaver/loadtime/WeavingURLClassLoader.java#L48
>> 
>> 
>> Alexander Kriegisch:
>> 
>> > I tried '-verbose:class' both with normal LTW configuration and with
>> > the weaving agent additionally prepended to the boot classpath via
>> > '-Xbootclasspath/p:/my/path/aspectjweaver.jar"'. Except for the weaver
>> > classes being loaded earlier in the latter case, the result is the
>> > same:
>> >
>> > Only classes from AppClassLoader yield any AspectJ log message, woven
>> > or not. JRE classes are being ignored, I see no other classloader
>> > being attached. Actually there does not seem to be any specific debug
>> > logging for names of attached classloaders at all, I only indirectly
>> > see things like "[AppClassLoader@18b4aac2] debug not weaving
>> > 'a.b..C'".
>> >
>> >
>> > Andy Clement:
>> >
>> >>> Furthermore, both '-verbose:class' and '-verbose=class' yield
>> >>> warnings
>> >>
>> >> That's not a weaver option, it is a JVM option for showing class
>> >> loading. I thought pairing that with the -debug weaver option might
>> >> show java types being loaded by the JVM and if there was no immediate
>> >> weaver message then they weren't getting to the weaver.
>> >>
>> >> It is interesting what classloaders weavers get attached to. I can't
>> >> what the current class loader hierarchy is in Java8 - do you only see
>> >> the one weaver attached to application related class loader?
>> >>
>> >>
>> >> Alexander Kriegisch:
>> >>
>> >>> Actually, I am still running Java 8, so modules are not an issue
>> >>> here.
>> >>>
>> >>> Furthermore, both '-verbose:class' and '-verbose=class' yield
>> >>> warnings:
>> >>>
>> >>> [MethodUtil@1e51f2fa] warning Cannot configure weaver with option
>> >>> '-verbose:class': unknown option
>> >>>
>> >>> I run with these settings:
>> >>>
>> >>> <weaver options="-showWeaveInfo -verbose -debug
>> >>> -Xset:weaveJavaxPackages=true,weaveJavaPackages=true">
>> >>> <include within="javax..*"/>
>> >>> <include within="java..*"/>
>> >>> <include within="org.aspectj..*"/>
>> >>> </weaver>
>> >>>
>> >>> I see nothing on the console indicating that any JRE classes are
>> >>> even visible to the classloader. I even created a main class
>> >>> starting my other main class via Class.forName(), Class.getMethod()
>> >>> and Method.invoke() in order to avoid javax or java JRE imports in
>> >>> my main class, trying to avoid that the weaver kicks in too late. It
>> >>> seems as if the weaver does not get attached to the right
>> >>> classloader. Should I do more than just '-javaagent:...' and also
>> >>> add the weaver to the boot classpath or something?
>> >>>
>> >>> I found a test related to javax classes, but that one is kinda
>> >>> cheating because it tests with own classes in javax package not with
>> >>> real JRE classes:
>> >>>
>> >>>
>> https://github.com/eclipse/org.aspectj/tree/master/tests/features160/weavingJavaxPackage
>> >>>
>> >>> I really need some help to get started here.
>> >>>
>> >>>
>> >>> Andy Clement:
>> >>>
>> >>>> I feel like they used to work but there were gotchas. For example
>> >>>> the JVM loads up some types before the LTW infrastructure can even
>> >>>> get involved and those can't be woven. I don't actually recall if
>> >>>> we have testcases for this but I wouldn't be surprised if they
>> >>>> weren't there. I guess you have tried them and they don't work - I
>> >>>> wonder if you were test weaving something that would be loaded
>> >>>> early? It would be interesting to attempt it with a -verbose:class
>> >>>> and verify not attempting to weave things loaded before the 'LTW is
>> >>>> active' type messages come out. Will it work with modules in recent
>> >>>> Javas? That seems unlikely.
>> >>>>
>> >>>> But it could be the kind of classloaders in use in regular Java now
>> >>>> don't allow weaver attachment, I honestly haven't kept up to speed
>> >>>> on that - and maybe that prevents them working at all. A run of LTW
>> >>>> with the debug option on for the weaver should show the types the
>> >>>> weaver is being exposed to. If those are java/javax then they
>> >>>> should be weavable.
>> >>>>
>> >>>>
>> >>>> Alexander Kriegisch:
>> >>>>
>> >>>>> The AspectJ documentation still mentions things like
>> >>>>>
>> >>>>> -Xset:weaveJavaxPackages=true
>> >>>>> -Xset:weaveJavaPackages=true
>> >>>>>
>> >>>>> or for LTW
>> >>>>>
>> >>>>> <include within="javax.*"/>
>> >>>>> <include within="java.*"/>
>> >>>>> <include within="org.aspectj.*"/>
>> >>>>>
>> >>>>> (I think "java..*" would be correct syntax, BTW.)
>> >>>>>
>> >>>>> None of these work. Yes, there are valid cases in which users
>> >>>>> might want to use LTW on JRE classes. The only way I could ever
>> >>>>> weave into the JRE (execution joinpoints, not just call from my
>> >>>>> own woven code) was binary weaving and creating my own (subset of)
>> >>>>> JRE, prepending it to the boot classpath. But that's not nice and
>> >>>>> I never tried with modularised Java 9+, which might work or not.
>> >>>>>
>> >>>>> Before I create a Bugzilla ticket I would like to get a maintainer
>> >>>>> opinion. Is there any chance to make this work with AspectJ LTW?
>> >>>>> Is is maybe possible already and I just do it wrong?
>> _______________________________________________
>> aspectj-users mailing list
>> aspectj-users@xxxxxxxxxxx
>> <mailto:aspectj-users@xxxxxxxxxxx> 
>> To unsubscribe from this list, visit
>> https://www.eclipse.org/mailman/listinfo/aspectj-users
>