Lataa Wasmtime 39.0.0

39.0.0
Released 2025-11-20.
Added
- Initial work has begun to support WebAssembly-level debugging natively in
Wasmtime. This is intended to complement today's preexisting DWARF-level
debugging, but this work will be portable and operate at the WebAssembly level
of abstraction rather than the machine-level. Note that this work is not yet
complete at this time but is expected to get filled out over the coming
releases.
#11768
#11769
#11873
#11892
#11895
- The pooling allocator now exposes more metrics about unused slots.
#11789
- The Wizer and component-init projects have been merged into Wasmtime under
a new wasmtime wizer CLI subcommand and wasmtime-wizer crate. This is
mostly a drop-in replacement for both with a minor caveat that the
initialization function is now called wizer-initialize instead of
wizer.initialize to be compatible with components.
#11805
#11851
#11853
#11855
#11857
#11863
#11866
#11867
#11877
#11876
#11878
#11891
#11897
#11898
- The Config::wasm_feature method is now public.
#11812
- Enabling the wasm exceptions proposal is now exposed in the C API.
#11861
- The wasmtime crate now has a custom-sync-primitives Cargo feature which
enables using custom synchronization primitives defined by the embedder. This
is useful in no_std targets where the default panic-on-contention primitives
are not appropriate.
#11836
- Wasmtime now supports unsafe intrinsics to be used for compile-time builtins.
This can be used to provide give low-level access to host APIs/memory to a
guest program in a controlled fashion.
#11825
#11918
- The signals_based_traps configuration option is now exposed in the C API.
#11879
- A new EqRef::from_i31 function has been added.
#11884
- The wasmtime serve subcommand will, by default, now reuse instances when
used with WASIp3 components. This increases throughput and additionally
showcases the concurrent features of WASIp3. This can be opted-out-of on the
CLI as well.
#11807
- The C++ API for components has been filled out and implemented.
#11880
#11889
#11988
- A new ResourceDynamic type, similar to Resource<T>, has been added to
support host resources that have a dynamic tag at runtime rather than a
statically known tag at compile time. This is then used to implement resources
in the C/C++ API as well.
#11885
#11920
- The C/C++ API of Wasmtime now supports the custom-page-sizes wasm proposal.
#11890
- Initial support has been added for the cooperative multithreading component
model proposal in Wasmtime, built on async primitives.
#11751
- The epoch_deadline_callback Rust API has been bound in C++.
#11945
- A new Request::into_http helper has been added to the WASIp3 implementation
of wasi:http.
#11843
- A define_unknown_imports_as_traps function has been added to the C API.
#11962
- A callback-based implementation of stdout and stderr has been added to the
C API for WASI configuration.
#11965
Changed
- Running async functions in the component model now operates at the
Store-level of abstraction rather than an Instance.
#11796
- The wasmtime serve subcommand no longer mistakenly spawns an epoch thread
per-request and instead uses a single epoch thread.
#11817
- The component-model-async Cargo feature is now on-by-default. Note that it
is still gated at runtime by default. Also note that Wasmtime 39 does not include
#12031 which means
that components using async produced with the latest wasm-tools will not run
in Wasmtime 39. To run async components it's recommended to pin to a
historical version of wasm-tools and guest toolchains for now.
#11822
- Bindings generated by wiggle no longer use async_trait.
#11839
- Wasmtime's documentation now has an example of a plugin system using Wasmtime.
#11848
- Profiling with perfmap or jitdump now uses O_APPEND to be more amenable to
other engines in the same process also using perfmap/jitdump.
#11865
- The wasmtime-wasi-http crate now uses UnsyncBoxBody to clarify that Sync
is not required.
#11941
- A . character is now used instead of / int he bindgen! macro to separate
interface members.
#11947
- The func_new function for component linkers now provides the type to the
callee so it knows the type that the component that imported it is using.
#11944
- The component::Func type now has a type accessor and the old params/result
accessors were deleted.
#11943
- Wasmtime now requires Rust 1.89.0 or later to compile.
#11959
Fixed
- Some panics handling shapes of components with resources in various locations
has been fixed.
#11798
- Bitwise float operations in Cranelift have been fixed on aarch64.
#11811
- An off-by-one in the bounds check of wasm atomic operations has been fixed.
#11977
- Bounds-check elision now happens again with 4 GiB guard pages.
#11973