cranelift

rust jit wasm webassembly runtime wasi cranelift sandbox wasmtime

Alex Crichton 2697a18d2f Redo the statically typed `Func` API (#2719 ) * Redo the statically typed `Func` API This commit reimplements the `Func` API with respect to statically typed dispatch. Previously `Func` had a `getN` and `getN_async` family of methods which were implemented for 0 to 16 parameters. The return value of these functions was an `impl Fn(..)` closure with the appropriate parameters and return values. There are a number of downsides with this approach that have become apparent over time: * The addition of `_async` doubled the API surface area (which is quite large here due to one-method-per-number-of-parameters). The [documentation of `Func`][old-docs] are quite verbose and feel "polluted" with all these getters, making it harder to understand the other methods that can be used to interact with a `Func`. * These methods unconditionally pay the cost of returning an owned `impl Fn` with a `'static` lifetime. While cheap, this is still paying the cost for cloning the `Store` effectively and moving data into the closed-over environment. * Storage of the return value into a struct, for example, always requires `Box`-ing the returned closure since it otherwise cannot be named. * Recently I had the desire to implement an "unchecked" path for invoking wasm where you unsafely assert the type signature of a wasm function. Doing this with today's scheme would require doubling (again) the API surface area for both async and synchronous calls, further polluting the documentation. The main benefit of the previous scheme is that by returning a `impl Fn` it was quite easy and ergonomic to actually invoke the function. In practice, though, examples would often have something akin to `.get0::<()>()?()?` which is a lot of things to interpret all at once. Note that `get0` means "0 parameters" yet a type parameter is passed. There's also a double function invocation which looks like a lot of characters all lined up in a row. Overall, I think that the previous design is starting to show too many cracks and deserves a rewrite. This commit is that rewrite. The new design in this commit is to delete the `getN{,_async}` family of functions and instead have a new API: impl Func { fn typed<P, R>(&self) -> Result<&Typed<P, R>>; } impl Typed<P, R> { fn call(&self, params: P) -> Result<R, Trap>; async fn call_async(&self, params: P) -> Result<R, Trap>; } This should entirely replace the current scheme, albeit by slightly losing ergonomics use cases. The idea behind the API is that the existence of `Typed<P, R>` is a "proof" that the underlying function takes `P` and returns `R`. The `Func::typed` method peforms a runtime type-check to ensure that types all match up, and if successful you get a `Typed` value. Otherwise an error is returned. Once you have a `Typed` then, like `Func`, you can either `call` or `call_async`. The difference with a `Typed`, however, is that the params/results are statically known and hence these calls can be much more efficient. This is a much smaller API surface area from before and should greatly simplify the `Func` documentation. There's still a problem where `Func::wrapN_async` produces a lot of functions to document, but that's now the sole offender. It's a nice benefit that the statically-typed-async verisons are now expressed with an `async` function rather than a function-returning-a-future which makes it both more efficient and easier to understand. The type `P` and `R` are intended to either be bare types (e.g. `i32`) or tuples of any length (including 0). At this time `R` is only allowed to be `()` or a bare `i32`-style type because multi-value is not supported with a native ABI (yet). The `P`, however, can be any size of tuples of parameters. This is also where some ergonomics are lost because instead of `f(1, 2)` you now have to write `f.call((1, 2))` (note the double-parens). Similarly `f()` becomes `f.call(())`. Overall I feel that this is a better tradeoff than before. While not universally better due to the loss in ergonomics I feel that this design is much more flexible in terms of what you can do with the return value and also understanding the API surface area (just less to take in). [old-docs]: https://docs.rs/wasmtime/0.24.0/wasmtime/struct.Func.html#method.get0 * Rename Typed to TypedFunc * Implement multi-value returns through `Func::typed` * Fix examples in docs * Fix some more errors * More test fixes * Rebasing and adding `get_typed_func` * Updating tests * Fix typo * More doc tweaks * Tweak visibility on `Func::invoke` * Fix tests again		4 years ago
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wasm	Wasmtime 0.13.0 and Cranelift 0.61.0. (#1398)	5 years ago
main.c	Update WebAssembly C API submodule to latest commit. (#2579)	4 years ago
main.rs	Redo the statically typed `Func` API (#2719)	4 years ago