RFR(M): 8165550: Add class loader names to ClassCastException message

[Mandy Chung]

> On Nov 11, 2016, at 3:13 AM, Daniel Fuchs <daniel.fuchs at oracle.com> wrote:
> 
> Hi,
> 
> On 10/11/16 23:24, David Holmes wrote:
>> Hi Rachel,
>> 
>> On 11/11/2016 8:31 AM, Rachel Protacio wrote:
>>> Ah yes, my apologies - I should have provided more context. This is the
>>> VM corollary of Mandy's change
>>> http://hg.openjdk.java.net/jdk9/dev/hotspot/rev/48fce55afe71 which
>>> implements the new classloader name scheme and uses it in Stack Traces.
>>> In the fullest instance, it could look like
>>>    MyClassLoader/module1 at 9.0/package1.class1
>>> The class loader is not listed if it is built-in, the module is not
>>> listed if it is unnamed, the version is not listed if it is a "non-jdk"
>>> module.
>> 
>> Ah I see. Though not at all clear why we would care about showing the
>> JDK module version ??
> 
> Mandy will correct me if I'm wrong, but AFAIU, for JDK modules,
> the version is displayed only if the module is an upgradeable
> module. The relevant algorithm [1] that does that can be seen in
> StackTraceElement::toLoaderModuleClassName(Class<?>):
> 

That is correct and that’s the format we implemented for the stack trace.

The VM does not have an easy way to determine if a JDK module is upgradeable or not.  There are a couple options that we considered for example include such information when defining the module.  The reason to include a version in an upgradeable module so that from the stack trace it can tell if the class is not the version in the JDK.   So we came up with this option such that the version is omitted if it’s a JDK module coming from the image that includes upgradeable modules that are not upgraded.  If these upgradeable modules are loaded from image, they are the same version as the runtime.  If the module is upgraded, the version will be included. 

We agree to not to change the JVM_DefineModule interface since jake changes are in flight.  The exception message will have a small difference but really minor and still provides the useful information for troubleshooting.

Mandy

> 
> [1] http://hg.openjdk.java.net/jdk9/dev/jdk/file/5b6b8e24a20b/src/java.base/share/classes/java/lang/StackTraceElement.java#l414
> 
> best regards,
> 
> -- daniel
> 
>