I had hoped that the VM interface for Class, Object, Thread and Throwable was usable for most VMs. What isn't in your case?
Although this question wasn't asked at me I'll answer on behalf of the JC implementation in case it may add something useful. This is just one data point and surely these reasons don't apply universally.
- I avoid VMFoo instances (i.e, shadow objects). It seems to me that storing VM specific info in a shadow object serves no (runtime) purpose: if it can be represented in Java, store it in the original object, if it can't store it in a native C structure or whatever.
- I used the type byte[] for all vmData fields.
- I prefer to avoid the extra method call overhead for important methods like Object.wait() imposed by the VMFoo split. In Classpath every Object.wait() requires calling VMObject.wait(). That makes the code separation cleaner but doesn't make implementation any easier - it's just as easy to implement Object.wait() as a native method as it is to implement VMObject.wait() as a native method.
- My Thread class uses private objects to implement sleep() and join() in terms of Object.wait(). The VM notify()'s this object when the thread exits. This means all the complexity of sleeping (and handling Thread.interrupt()) can be put in Object.wait() and not duplicated elsewhere.
- I folded VMThrowable into Throwable to get rid of VMThrowable. Same reasons as mentioned above.
- These bugs (not fixed in Classpath 0.07): http://savannah.gnu.org/bugs/?func=detailitem&item_id=6938 http://savannah.gnu.org/bugs/?func=detailitem&item_id=7084
- Classpath's reflection implementation is/was incomplete and required modifications to work.
Hope these don't sound like complaints - using Classpath has worked out great and I'm very appreciative of it!!
Cheers, -Archie
__________________________________________________________________________ Archie Cobbs * CTO, Awarix * http://www.awarix.com
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