Re: [rvm-research] Reflection doubt

Hi,

On 13.07.2015 22:55, Guido Chari wrote:
> In particular... are the main components of the Jikes VM observable [...] at run-time? 
VM classes are visible to the application program because we don't have a clean classloader architecture that could prevent this. So you could call into the VM to observe certain state if you want to.

> Is it possible for instance to change a bytecode implementation or the layout of an object at run-time without recompiling the system.
That's currently not possible. You can't replace any of the core components at runtime:
- the bytecode implementation depends on the compiler and can't be replaced independently
- the Jikes RVM currently only supports a single object model (AFAIK the object layout was changeable at build time in the past)
- the garbage collector is chosen at build time

There has been research about better modularity in Java virtual machines, e.g. in the Maxine project. I don't know if the Maxine virtual machine allows switching of components at runtime but I would doubt it. The metacircularity of the Jikes RVM and Maxine might impose certain constraints. You would need a way to ensure that a switch of components doesn't cause inconsistencies with the core parts of the VM (e.g the boot image) that have already been compiled with the old components. I'm not sure how that could work but I've got to admit that I haven't looked at this problem at all.


Kind regards,

Erik Brangs


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