c-api: Remove allocations from wasmtime_val_t
#8451
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This commit redesigns how GC references work in the C API. previously
`wasmtime_{any,extern}ref_t` were both opaque pointers in the C API
represented as a `Box`. Wasmtime did not, however, provide the ability
to deallocate just the `Box` part. This was intended to be handled with
unrooting APIs but unrooting requires a `wasmtime_context_t` parameter,
meaning that destructors of types in other languages don't have a
suitable means of managing the memory around the
`wasmtime_{any,extern}ref_t` which might lead to leaks.
This PR takes an alternate approach for the representation of these
types in the C API. Instead of being an opaque pointer they're now
actual structures with definitions in the header file. These structures
mirror the internals in Rust and Rust is tagged to ensure that changes
are reflected in the C API as well. This is similar to how
`wasmtime_func_t` matches `wasmtime::Func`. This enables embedders to
not need to worry about memory management of these values outside of the
manual rooting otherwise required.
The hope is that this will reduce the likelihood of memory leaks and
otherwise not make it any harder to manage references in the C API.
fitzgen
approved these changes
Apr 23, 2024
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| const _: () = { | ||
| // NB: these match the C API which should also be updated if this changes | ||
| assert!(std::mem::size_of::<GcRootIndex>() == 16); | ||
| assert!(std::mem::align_of::<GcRootIndex>() == 8); | ||
| }; |
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Maybe these asserts should be for ManuallyRooted rather than GcRootIndex, just so that if we add a field to the former, but leave the latter as-is, we get build errors because that mismatch would introduce unsafety.
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Try to avoid using a `transmute` in the implementation of the C API and instead use a `union` like is being done in bytecodealliance#8451. Additionally add some helper functions to the header to work with null funcref values instead of only documenting the implementation.
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* c-api: Tidy up some `wasmtime_func_t` usage Try to avoid using a `transmute` in the implementation of the C API and instead use a `union` like is being done in #8451. Additionally add some helper functions to the header to work with null funcref values instead of only documenting the implementation. * Try to fix doxygen
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This includes updates for: - bytecodealliance/wasmtime#8451 - bytecodealliance/wasmtime#8461 - bytecodealliance/wasmtime#8011 TODOs: - Allocating an `externref` can now fail (by `wasmtime_externref_new` returning `false`). Currently, we throw a `WasmtimeException` in that case. We need to check where that exception can be thrown, and whether we need to do any additional clean-up (e.g. when converting arguments for a function call). - Check whether it's ok to compare the `__private` field of externs (which has been remaned in the C API, previously it was `index`). - `anyref` type is not yet supported, but I'm not sure what exactly it is and whether we need to add it. Fixes bytecodealliance#315
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* Update to recent Wasmtime C API changes regarding values. This includes updates for: - bytecodealliance/wasmtime#8451 - bytecodealliance/wasmtime#8461 - bytecodealliance/wasmtime#8011 TODOs: - Allocating an `externref` can now fail (by `wasmtime_externref_new` returning `false`). Currently, we throw a `WasmtimeException` in that case. We need to check where that exception can be thrown, and whether we need to do any additional clean-up (e.g. when converting arguments for a function call). - Check whether it's ok to compare the `__private` field of externs (which has been remaned in the C API, previously it was `index`). - `anyref` type is not yet supported, but I'm not sure what exactly it is and whether we need to add it. Fixes #315 * Follow-Up: Make fields private. * Ensure to clean-up `Value` instances (in arguments for a function call, and in results for an untyped callback) when e.g. allocating an `externref` fails. We don't need to do such a clean-up for unchecked function calls that use `ValueRaw` because in that case we don't own `externref` values. * Avoid accessing the `__private` fields in tests by checking the whole struct for equality (which is the case when all members are equal). * Use separate dictionaries for caching `Function`, `Memory`, and `Global` objects in the `Store`, which avoids having to explicitly accessing the `__private` field (because the whole struct is now compared). Additionally, it is more type-safe (since we don't need to cast the `object`).
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This commit redesigns how GC references work in the C API. previously
wasmtime_{any,extern}ref_twere both opaque pointers in the C API represented as aBox. Wasmtime did not, however, provide the ability to deallocate just theBoxpart. This was intended to be handled with unrooting APIs but unrooting requires awasmtime_context_tparameter, meaning that destructors of types in other languages don't have a suitable means of managing the memory around thewasmtime_{any,extern}ref_twhich might lead to leaks.This PR takes an alternate approach for the representation of these types in the C API. Instead of being an opaque pointer they're now actual structures with definitions in the header file. These structures mirror the internals in Rust and Rust is tagged to ensure that changes are reflected in the C API as well. This is similar to how
wasmtime_func_tmatcheswasmtime::Func. This enables embedders to not need to worry about memory management of these values outside of the manual rooting otherwise required.The hope is that this will reduce the likelihood of memory leaks and otherwise not make it any harder to manage references in the C API.