RFR(M): 8199852: Print more information about class loaders in LinkageErrors.

[Lindenmaier, Goetz]

... wherever I report the class and it's loader I 
will use class_loader_and_module_name() if I manage
to usefully extend it's information about the classloaders. ...

> -----Original Message-----
> From: Lindenmaier, Goetz
> Sent: Wednesday, March 21, 2018 9:21 PM
> To: 'Lois Foltan' <lois.foltan at oracle.com>; hotspot-runtime-
> dev at openjdk.java.net
> Subject: RE: RFR(M): 8199852: Print more information about class loaders in
> LinkageErrors.
> 
> Hi Lois,
> 
> The intention to normalize the output makes completely sense.
> It starts with using external_name everywhere ��.
> 
> But you need a method that reports about a classloader that does
> not belong to a class. There are places where I want to report three
> class loaders, but only one class name.
> 
> For example: "classloader A can not load class B because ..."
> 
> Also, as I understand, the class loader can be in a different module
> than the loaded class. So you might want to report both. (Well,
> this could be handled by the enum you describe).
> 
> I'll read the docu you mention.  I already had a look at the test
> you mention, but it seemed not to fit for the messages here.
> If the tests pass, I will post another change for IllegalAccessError
> that uses the same method. I wanted to hold that back until
> this one is finished, but maybe it makes sense to look at all the
> messages at a time.
> 
> Please also have a look at the wording of the new messages in the
> bug description.
> https://bugs.openjdk.java.net/browse/JDK-8199852
> https://bugs.openjdk.java.net/browse/JDK-8199940
> 
> Best regards,
>   Goetz.
> 
> 
> > -----Original Message-----
> > From: Lois Foltan [mailto:lois.foltan at oracle.com]
> > Sent: Wednesday, March 21, 2018 8:27 PM
> > To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
> > dev at openjdk.java.net
> > Subject: Re: RFR(M): 8199852: Print more information about class loaders in
> > LinkageErrors.
> >
> > On 3/21/2018 3:06 PM, Lois Foltan wrote:
> >
> > > On 3/21/2018 9:03 AM, Lindenmaier, Goetz wrote:
> > >
> > >> Hi Lois,
> > >>
> > >> Thanks for looking at this!
> > >>
> > >> I had a look at Klass::class_loader_and_module_name(), but there are
> > >> places
> > >> where you only want to report the class loader information, therefore I
> > >> decided to do it this way. (If you like this, I have more of these in
> > >> work :)).
> > >> For example see expectedErrorMessageDuplicate1 in the test.
> > >> Also, there might just be a classloader at hand, not a class as needed
> > >> for that method.
> > >>
> > >> But maybe it would make sense to call describe_external() in
> > >> class_loader_and_module_name() to get more information about
> > >> the classloader?
> > >
> > > Hi Goetz,
> > >
> > > In the JDK 9 time frame we strove to construct the string representing
> > > the class loader, module name & module version in a defined,
> > > structured manner.  This allows for consistency across error messages,
> > > stack dumps, etc.  Use of Klass::class_loader_and_name() gives us this
> > > consistency and you can see some examples of its use in
> > > ClassCastException messages. See,
> > > https://bugs.openjdk.java.net/browse/JDK-8165550 and the test,
> > > test/hotspot/jtreg/runtime/modules/CCE_module_message.java. I
> > strongly
> > > encourage you to use Klass::class_loader_and_name() and not add
> > > describe_external().  Klass::class_loader_and_name() could be enhanced
> > > to take an enum parameter that allows for tailoring of the message
> > > itself, for example including/not including the module name when
> > > available, including the parent loader, etc.  It could be pulled out
> > > of Klass for use to obtain a class loader's name when a Klass is not
> > > available, although Coleen just recently moved it to Klass.  I would
> > > support this type of change.
> > See the javadoc for java.lang.StackTraceElement,
> >
> https://docs.oracle.com/javase/9/docs/api/java/lang/StackTraceElement.ht
> > ml.
> > Specifically the API Note in the StackTraceElement.toString()
> > description which documents the format and contains examples.
> > Lois
> >
> > >
> > > Thanks,
> > > Lois
> > >
> > >>
> > >> Best regards,
> > >>    Goetz.
> > >>
> > >>
> > >>
> > >>> -----Original Message-----
> > >>> From: Lois Foltan [mailto:lois.foltan at oracle.com]
> > >>> Sent: Mittwoch, 21. März 2018 13:22
> > >>> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-
> > runtime-
> > >>> dev at openjdk.java.net
> > >>> Subject: Re: RFR(M): 8199852: Print more information about class
> > >>> loaders in
> > >>> LinkageErrors.
> > >>>
> > >>> On 3/21/2018 7:55 AM, Lindenmaier, Goetz wrote:
> > >>>
> > >>>> Hi,
> > >>>>
> > >>>> ClassLoaders have a field containing a name since Java 9.
> > >>>>
> > >>>> This change improves some of the messages of LinkageErrors to
> > >>>> print the name of the loader involved, as well as the parent of the
> > >>>> loader.
> > >>>> This simplifies tracking down the component causing an error in large
> > >>>> Java systems.
> > >>>>
> > >>>> Please review:
> > >>>> http://cr.openjdk.java.net/~goetz/wr18/8199852-
> > >>> exMsg_Linkage/01/index.html
> > >>>> I ran this through all our tests (jck, jtreg, spec etc).  I will
> > >>>> run it through
> > >>> submit-hs
> > >>>> (or jdk/submit) once it's reviewed.
> > >>>>
> > >>>> Best regards,
> > >>>>     Goetz.
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>> Hi Goetz,
> > >>>
> > >>> This looks promising and something that we started to do in the JDK 9
> > >>> time frame.  Instead of adding the new method
> > >>> java_lang_ClassLoader::describe_external() can you possible
> > use/improve
> > >>> upon Klass::class_loader_and_module_name() in order to avoid
> > duplicate
> > >>> code?
> > >>>
> > >>> Thanks,
> > >>> Lois
> > >