MoarVM VS bumpalo

Implement return prioritization #1786: superseeded

Now, as to how that's done at the low level, and whether the way it's done is a good way to do it, well, I can't help. Suffice to say, the main place to look for how this is handled at the low-level is MoarVM. I dug around for a couple minutes and have a link to a commit from nearly a decade ago. Does that help?

For a class the default representation is P6Opaque. This is one of a few dozen stock representations that Raku requires compiler backends implement as standard. See, for example, the 46 .c/.h pairs of C89 source files in the relevant MoarVM directory. A quick glance at the names of the source code files should paint a broad picture. A look at their code will fill in some details.

I'm hoping someone who knows C89 can take a quick gander at the C89 code implementing 47 representations in here and comment on it.

This is (yet another) very un(der)documented Raku feature (over a decade after it was introduced!), but one can browse what looks to me like reasonably clean and commented C89 code implementing 47 representations in the relevant MoarVM directory.

FROM alpine:latest as base ARG RAKU_RELEASE=2021.12 ENV PKGS="git make gcc musl-dev perl linux-headers bash" RUN apk update && apk upgrade \ && apk add --no-cache $PKGS \ && git clone --depth 1 --branch ${RAKU_RELEASE} https://github.com/MoarVM/MoarVM.git \ && cd MoarVM \ && perl Configure.pl --prefix /usr \ && make --print-data-base \ && make install\ && cd .. \ && git clone --depth 1 --branch ${RAKU_RELEASE} git://github.com/Raku/nqp.git \ && cd nqp \ && perl Configure.pl --backends=moar --prefix /usr \ && make install \ && cd .. \ && git clone --depth 1 --branch ${RAKU_RELEASE} https://github.com/rakudo/rakudo.git \ && cd rakudo \ && perl Configure.pl --backends=moar --prefix /usr \ && make install \ && ls /usr/share/nqp/ FROM alpine:latest ARG UID=1000 LABEL version="0.5.0" maintainer="[email protected]" raku_release=${RAKU_RELEASE} raku_user_uid=${UID} COPY --from=base /usr/lib/libmoar.so /usr/lib COPY --from=base /usr/share/nqp/ /usr/share/nqp COPY --from=base /usr/share/perl6/ /usr/share/perl6 COPY --from=base /usr/bin/moar /usr/bin/nqp /usr/bin/raku /usr/bin/perl6 /usr/bin/rakudo /usr/bin/ RUN mkdir /github \ && addgroup -S raku && adduser -S raku -G raku --uid ${UID} USER raku WORKDIR /home/raku ENTRYPOINT ["raku"]

Visit the MoarVM project's home page and/or its github repo.

MoarVM's representation is very cool https://github.com/MoarVM/MoarVM/blob/master/docs/strings.asciidoc

Long story short, heap allocation is painfully slow. Any sort of malloc will always be slower than a custom pool or a bump allocator, because it has a lot more context to deal with.

Rust makes it especially hard to use custom allocators, see bumpalo for example [0]. To be fair, progress is being made in this area [1].

Theoretically one can use a "handle table" as a replacement for pools, you can find relevant discussion at [2].

[0] https://github.com/fitzgen/bumpalo

There are ways to accomplish this as well. Different allocator libraries exist for this kind of scenario, namely bumpallo which allocates a larger block of memory from the kernel, and allocates quickly thereafter. That would amortize the cost of memory allocations in the way I think you're after?

Meaning, storing a lot of things in the same block of allocated memory? Vec is a thing, you know. There's also a bump allocator library.

There are data structures like slotmap, and relatively low-level crates like bumpalo. This is not to say that either fits your use case, just that you definitely have access to the necessary parts to fit what you describe.

Sometimes you can put everything in a bump allocator, then when you're done, free the entire bump allocator in one go. https://docs.rs/bumpalo/

This is useful with crates like bumpalo which give you bump-allocation arenas whose lifetimes are tied to the objects they allocate.

TSC doesn't need to "stick around", right? Just a run-once and the program is over?

In those cases, https://github.com/fitzgen/bumpalo works amazingly as an arena. You can pretty much forget about reference counting and have direct references everywhere in your graph. The disadvantage is that it's hard to modify your tree without leaving memory around.

We use it extensively in http://github.com/dioxusLabs/dioxus and don't need to worry about Rc anywhere in the graph/diffing code.

Probably bumpalo, but then its Box will have a lifetime parameter - bumpalo::boxed::Box<'a, dyn MyTrait>

Strictly speaking, Rust doesn't need this as a built-in language feature, because its design allows it to be implemented as a third-party library: https://docs.rs/bumpalo

The biggest problem is that there's some awkwardness around RAII; I'm not sure whether that could have been avoided with a different approach.

Of course, ideally you'd want it to be compatible with the standard-library APIs that allocate. This is implemented, but is not yet at the point where they're sure they won't want to make backwards-incompatible changes to it, so you can only use it on nightly. https://doc.rust-lang.org/stable/std/alloc/trait.Allocator.h...

Or are you suggesting that the choice of allocator should be dynamically scoped, so that allocations that occur while the bump allocator is alive automatically use it even if they're in code that doesn't know about it? I think it's not possible for that to be memory-safe; all allocations using the bump allocator need to know about its lifetime, so that they can be sure not to outlive it, which would cause use-after-free bugs. I'm assuming that Odin just makes the programmer responsible for this, and if they get it wrong then memory corruption might occur; for a memory-safe language like Rust, that's not acceptable.