[dev-servo] Rooting APIs and idiomatic Rust
I have a branch of rust-mozjs where I attempted to implement a Rust version of CustomAutoRooter/AutoGCRooter from SpiderMonkey: https://github.com/jdm/rust-mozjs/commit/ff89d9609e17e7727c038c8ea8deab88bae4333e This compiles fine, but I hit problems when I attempted to integrate it with my previous work for a safe Rust interface to SM's typed arrays: https://github.com/servo/servo/pull/6779 Specifically, my problems stem from this - given that creating a typed array is fallible, as is wrapping an existing typed array reflector, we decided to make the constructors for the typed array APIs return Result values. Unfortunately this interacts poorly with AutoGCRooter, since it stores pointers to Rust objects that end up moving when unwrapping the Result (https://github.com/jdm/rust-mozjs/commit/ff89d9609e17e7727c038c8ea8deab88bae4333e#diff-5f5de62bd671c7658b23fd6be60ce6bfR41). Can anybody think of a useful way around this problem, or are we doomed to non-idiomatic APIs when we're trying to directly integrate with SM's lists of rooted values? ___ dev-servo mailing list dev-servo@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-servo
Re: [dev-servo] Rooting APIs and idiomatic Rust
CC-ing some SpiderMonkey GC people. Terrence, I know that you did some Rust stuff recently, so maybe you have the required bits of information to comment on this? On Wed, Sep 23, 2015 at 7:15 PM, Josh Matthews wrote: > I have a branch of rust-mozjs where I attempted to implement a Rust > version of CustomAutoRooter/AutoGCRooter from SpiderMonkey: > https://github.com/jdm/rust-mozjs/commit/ff89d9609e17e7727c038c8ea8deab88bae4333e > > This compiles fine, but I hit problems when I attempted to integrate it > with my previous work for a safe Rust interface to SM's typed arrays: > https://github.com/servo/servo/pull/6779 > > Specifically, my problems stem from this - given that creating a typed > array is fallible, as is wrapping an existing typed array reflector, we > decided to make the constructors for the typed array APIs return Result > values. Unfortunately this interacts poorly with AutoGCRooter, since it > stores pointers to Rust objects that end up moving when unwrapping the > Result ( > https://github.com/jdm/rust-mozjs/commit/ff89d9609e17e7727c038c8ea8deab88bae4333e#diff-5f5de62bd671c7658b23fd6be60ce6bfR41 > ). > > Can anybody think of a useful way around this problem, or are we doomed to > non-idiomatic APIs when we're trying to directly integrate with SM's lists > of rooted values? > ___ > dev-servo mailing list > dev-servo@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-servo > ___ dev-servo mailing list dev-servo@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-servo
Re: [dev-servo] Rooting APIs and idiomatic Rust
On Wed, Sep 23, 2015 at 11:01 AM, Till Schneidereit <
t...@tillschneidereit.net> wrote:
> CC-ing some SpiderMonkey GC people.
>
> Terrence, I know that you did some Rust stuff recently, so maybe you have
> the required bits of information to comment on this?
>
> On Wed, Sep 23, 2015 at 7:15 PM, Josh Matthews
> wrote:
>
>> I have a branch of rust-mozjs where I attempted to implement a Rust
>> version of CustomAutoRooter/AutoGCRooter from SpiderMonkey:
>> https://github.com/jdm/rust-mozjs/commit/ff89d9609e17e7727c038c8ea8deab88bae4333e
>>
>> This compiles fine, but I hit problems when I attempted to integrate it
>> with my previous work for a safe Rust interface to SM's typed arrays:
>> https://github.com/servo/servo/pull/6779
>>
>> Specifically, my problems stem from this - given that creating a typed
>> array is fallible, as is wrapping an existing typed array reflector, we
>> decided to make the constructors for the typed array APIs return Result
>> values. Unfortunately this interacts poorly with AutoGCRooter, since it
>> stores pointers to Rust objects that end up moving when unwrapping the
>> Result (
>> https://github.com/jdm/rust-mozjs/commit/ff89d9609e17e7727c038c8ea8deab88bae4333e#diff-5f5de62bd671c7658b23fd6be60ce6bfR41
>> ).
>>
>> Can anybody think of a useful way around this problem, or are we doomed
>> to non-idiomatic APIs when we're trying to directly integrate with SM's
>> lists of rooted values?
>>
>
I think we've already solved this for you from the C++ side, although it
will probably take a bit of new rust wrapping to make work. The weirdness
with the AutoFooRooters is that they conflate traceability with root
creation/destruction. We're currently working to move everything over to a
world where things can be traceable -- derives from JS::Traceable in C++ or
implements the Traceable trait in rust -- as a separate concept from
JS::Rooted. The upshot is twofold: first you can have Rooted;
secondly, (and more relevantly for your particular problem) is that
construction is decisively split from the initialization of the Rooted. In
C++ terms this looks like:
The old way:
class Foo : public CustomAutoRooter {
virtual void trace(JSTracer*) {}
};
Foo foo(cx, ...args...);
The new way:
class Foo : public JS::Traceable {
static void trace(Foo* self, JSTracer* trc) {}
};
Rooted foo(cx, Foo(...args...)); // Note the separate Foo and Rooted
constructors.
In Mozilla's C++ dialect, these two are roughly equivalent because fallible
init goes though a manual |bool init(...args...)| function after rooting
(and the tracer needs to deal with partial init). In the rust world that I
envision, you'd be able to fallibly construct something like (please excuse
me if my rust ideoms are old /and/ shaky):
let foo: Rooted = match Foo::new(..args..) {
Err(err) => handleErr!(...),
Ok(foo) => Rooted(foo)
};
Does this help at all or have I totally misunderstood the problem you are
facing? Please ping me on IRC and we can discuss this! The GC team is now
actively churning towards a simpler (and ideally C-wrappable) API and I'd
like to make sure we're all on the same page.
> ___
>> dev-servo mailing list
>> dev-servo@lists.mozilla.org
>> https://lists.mozilla.org/listinfo/dev-servo
>>
>
>
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Re: [dev-servo] Rooting APIs and idiomatic Rust
On 2015-09-23 5:49 PM, Terrence Cole wrote:
In Mozilla's C++ dialect, these two are roughly equivalent because fallible
init goes though a manual |bool init(...args...)| function after rooting
(and the tracer needs to deal with partial init). In the rust world that I
envision, you'd be able to fallibly construct something like (please excuse
me if my rust ideoms are old /and/ shaky):
let foo: Rooted = match Foo::new(..args..) {
Err(err) => handleErr!(...),
Ok(foo) => Rooted(foo)
};
Does this help at all or have I totally misunderstood the problem you are
facing? Please ping me on IRC and we can discuss this! The GC team is now
actively churning towards a simpler (and ideally C-wrappable) API and I'd
like to make sure we're all on the same page.
This looks like a plausible solution to my problem. Nevertheless, it
looks like if Foo::new returns a value which contains GC pointers then
it's a potential hazard, right?
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