812c8ef3686aca95d9f43d1fe541fa9c9557c528
6 Commits
| Author | SHA1 | Message | Date | |
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Alex Crichton
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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
|
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Alex Crichton
|
918c012d00 |
Fix some issues around TLS management with async (#2709)
This commit fixes a few issues around managing the thread-local state of a wasmtime thread. We intentionally only have a singular TLS variable in the whole world, and the problem is that when stack-switching off an async thread we were not restoring the previous TLS state. This is necessary in two cases: * Futures aren't guaranteed to be polled/completed in a stack-like fashion. If a poll sees that a future isn't ready then we may resume execution in a previous wasm context that ends up needing the TLS information. * Futures can also cross threads (when the whole store crosses threads) and we need to save/restore TLS state from the thread we're coming from and the thread that we're going to. The stack switching issue necessitates some more glue around suspension and resumption of a stack to ensure we save/restore the TLS state on both sides. The thread issue, however, also necessitates that we use `#[inline(never)]` on TLS access functions and never have TLS borrows live across a function which could result in running arbitrary code (as was the case for the `tls::set` function. |
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Peter Huene
|
54c07d8f16 |
Implement shared host functions. (#2625)
* Implement defining host functions at the Config level. This commit introduces defining host functions at the `Config` rather than with `Func` tied to a `Store`. The intention here is to enable a host to define all of the functions once with a `Config` and then use a `Linker` (or directly with `Store::get_host_func`) to use the functions when instantiating a module. This should help improve the performance of use cases where a `Store` is short-lived and redefining the functions at every module instantiation is a noticeable performance hit. This commit adds `add_to_config` to the code generation for Wasmtime's `Wasi` type. The new method adds the WASI functions to the given config as host functions. This commit adds context functions to `Store`: `get` to get a context of a particular type and `set` to set the context on the store. For safety, `set` cannot replace an existing context value of the same type. `Wasi::set_context` was added to set the WASI context for a `Store` when using `Wasi::add_to_config`. * Add `Config::define_host_func_async`. * Make config "async" rather than store. This commit moves the concept of "async-ness" to `Config` rather than `Store`. Note: this is a breaking API change for anyone that's already adopted the new async support in Wasmtime. Now `Config::new_async` is used to create an "async" config and any `Store` associated with that config is inherently "async". This is needed for async shared host functions to have some sanity check during their execution (async host functions, like "async" `Func`, need to be called with the "async" variants). * Update async function tests to smoke async shared host functions. This commit updates the async function tests to also smoke the shared host functions, plus `Func::wrap0_async`. This also changes the "wrap async" method names on `Config` to `wrap$N_host_func_async` to slightly better match what is on `Func`. * Move the instance allocator into `Engine`. This commit moves the instantiated instance allocator from `Config` into `Engine`. This makes certain settings in `Config` no longer order-dependent, which is how `Config` should ideally be. This also removes the confusing concept of the "default" instance allocator, instead opting to construct the on-demand instance allocator when needed. This does alter the semantics of the instance allocator as now each `Engine` gets its own instance allocator rather than sharing a single one between all engines created from a configuration. * Make `Engine::new` return `Result`. This is a breaking API change for anyone using `Engine::new`. As creating the pooling instance allocator may fail (likely cause is not enough memory for the provided limits), instead of panicking when creating an `Engine`, `Engine::new` now returns a `Result`. * Remove `Config::new_async`. This commit removes `Config::new_async` in favor of treating "async support" as any other setting on `Config`. The setting is `Config::async_support`. * Remove order dependency when defining async host functions in `Config`. This commit removes the order dependency where async support must be enabled on the `Config` prior to defining async host functions. The check is now delayed to when an `Engine` is created from the config. * Update WASI example to use shared `Wasi::add_to_config`. This commit updates the WASI example to use `Wasi::add_to_config`. As only a single store and instance are used in the example, it has no semantic difference from the previous example, but the intention is to steer users towards defining WASI on the config and only using `Wasi::add_to_linker` when more explicit scoping of the WASI context is required. |
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Peter Huene
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505437e353 |
Code cleanup.
Last minute code clean up to fix some comments and rename `address_space_size` to `memory_reservation_size` to better describe what the option is doing. |
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Peter Huene
|
e71ccbf9bc |
Implement the pooling instance allocator.
This commit implements the pooling instance allocator. The allocation strategy can be set with `Config::with_allocation_strategy`. The pooling strategy uses the pooling instance allocator to preallocate a contiguous region of memory for instantiating modules that adhere to various limits. The intention of the pooling instance allocator is to reserve as much of the host address space needed for instantiating modules ahead of time and to reuse committed memory pages wherever possible. |
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Alex Crichton
|
7795a230f2 |
Implement support for async functions in Wasmtime (#2434)
* Implement support for `async` functions in Wasmtime This is an implementation of [RFC 2] in Wasmtime which is to support `async`-defined host functions. At a high level support is added by executing WebAssembly code that might invoke an asynchronous host function on a separate native stack. When the host function's future is not ready we switch back to the main native stack to continue execution. There's a whole bunch of details in this commit, and it's a bit much to go over them all here in this commit message. The most important changes here are: * A new `wasmtime-fiber` crate has been written to manage the low-level details of stack-switching. Unixes use `mmap` to allocate a stack and Windows uses the native fibers implementation. We'll surely want to refactor this to move stack allocation elsewhere in the future. Fibers are intended to be relatively general with a lot of type paremters to fling values back and forth across suspension points. The whole crate is a giant wad of `unsafe` unfortunately and involves handwritten assembly with custom dwarf CFI directives to boot. Definitely deserves a close eye in review! * The `Store` type has two new methods -- `block_on` and `on_fiber` which bridge between the async and non-async worlds. Lots of unsafe fiddly bits here as we're trying to communicate context pointers between disparate portions of the code. Extra eyes and care in review is greatly appreciated. * The APIs for binding `async` functions are unfortunately pretty ugly in `Func`. This is mostly due to language limitations and compiler bugs (I believe) in Rust. Instead of `Func::wrap` we have a `Func::wrapN_async` family of methods, and we've also got a whole bunch of `Func::getN_async` methods now too. It may be worth rethinking the API of `Func` to try to make the documentation page actually grok'able. This isn't super heavily tested but the various test should suffice for engaging hopefully nearly all the infrastructure in one form or another. This is just the start though! [RFC 2]: https://github.com/bytecodealliance/rfcs/pull/2 * Add wasmtime-fiber to publish script * Save vector/float registers on ARM too. * Fix a typo * Update lock file * Implement periodically yielding with fuel consumption This commit implements APIs on `Store` to periodically yield execution of futures through the consumption of fuel. When fuel runs out a future's execution is yielded back to the caller, and then upon resumption fuel is re-injected. The goal of this is to allow cooperative multi-tasking with futures. * Fix compile without async * Save/restore the frame pointer in fiber switching Turns out this is another caller-saved register! * Simplify x86_64 fiber asm Take a leaf out of aarch64's playbook and don't have extra memory to load/store these arguments, instead leverage how `wasmtime_fiber_switch` already loads a bunch of data into registers which we can then immediately start using on a fiber's start without any extra memory accesses. * Add x86 support to wasmtime-fiber * Add ARM32 support to fiber crate * Make fiber build file probing more flexible * Use CreateFiberEx on Windows * Remove a stray no-longer-used trait declaration * Don't reach into `Caller` internals * Tweak async fuel to eventually run out. With fuel it's probably best to not provide any way to inject infinite fuel. * Fix some typos * Cleanup asm a bit * Use a shared header file to deduplicate some directives * Guarantee hidden visibility for functions * Enable gc-sections on macOS x86_64 * Add `.type` annotations for ARM * Update lock file * Fix compile error * Review comments |