Re: basic questions on MPS

[Vibhav Pant <vibhavp@gmail.com>]

On Thu, Apr 25, 2024 at 11:23 PM Helmut Eller <eller.helmut@gmail.com> wrote:
>
> I'd also have some MPS related questions.  Just curiosity.
>
> 1) Does somebody have experience with this MMTK [https://www.mmtk.io/]?
> How does it compare to MPS?
>

From my understanding, MMTk is a *framework* for writing a memory
manager + an API for allocating and working with allocated memory. A
language runtime being "ported" to MMTk seems to involve these two
things:
* The language's VM and memory management model needs to be thoroughly
known to MMTk. It should know how objects addresses in the language
look like, where and how their metadata gets stored and loaded, how
copy semantics are implemented, etc
(https://docs.rs/mmtk/latest/mmtk/vm/trait.VMBinding.html).
* The language runtime calls *into* MMTk's language-agnostic memory
management API for allocating memory, setting metadata, attach
finalizers, etc. Even stuff like pointer arithmetic needs to be done
through MMTk, as the language runtime code cannot make any assumptions
about the memory model.

Once that's done, a program can choose which GC algorithm it would
like to use during runtime
(https://docs.mmtk.io/api/mmtk/util/options/enum.PlanSelector.html).
MMTk/mmtk-core by itself does not "support" any languages, as one goal
of the project seems to be to provide a way to write garbage
collection algorithms for an abstract virtual machine.

Perhaps not the same thing, but a similar idea is LLVM's support for
GC (https://llvm.org/docs/GarbageCollection.html), as LLVM IR code
generated by a compiler in such a case uses special instrinsics for
fiddling with pointer metadata, declaring write and load barriers,
etc, with the basic idea being that LLVM knows everything about
managed objects in the language runtime. You can then write a garbage
collector as an LLVM plugin, which theoretically can be loaded at
runtime.

Vibhav
---
Vibhav Pant
vibhavp@gmail.com
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