Currently fast ops will always check for the alignment of a TypedArray
when getting a slice out of them. A match is then done to ensure that
some slice was received and if not a fallback will be requested.
For Uint8Arrays (and WasmMemory which is equivalent to a Uint8Array) the
alignment will always be okay. Rust probably optimises this away for the
most part (since the Uint8Array check is `x % 1 != 0`), but what it
cannot optimise away is the fast ops path's request for fallback options
parameter.
The extra parameter's cost is likely negligible but V8 will need to
check if a fallback was requested and prepare the fallback call just in
case it was. In the future the lack of a fallback may also enable V8 to
much better optimise the result handling.
For V8 created buffers, it seems like all buffers are actually always
guaranteed to be properly aligned: All buffers seem to always be created
8-byte aligned, and creating a 32 bit array or 64 bit array with a
non-aligned offset from an ArrayBuffer is not allowed. Unfortunately,
Deno FFI cannot give the same guarantees, and it is actually possible
for eg. 32 bit arrays to be created unaligned using it. These arrays
work fine (at least on Linux) so it seems like this is not illegal, it
just means that we cannot remove the alignment checking for 32 bit
arrays.
Fixes https://github.com/denoland/deno/issues/16934
Example compiler error:
```
error: mutable opstate is not supported in async ops
--> core/ops_builtin.rs:122:1
|
122 | #[op]
| ^^^^^
|
= note: this error originates in the attribute macro `op` (in Nightly builds, run with -Z macro-backtrace for more info)
```
Uses SeqOneByteString optimization to do zero-copy `&str` arguments in
fast calls.
- [x] Depends on https://github.com/denoland/rusty_v8/pull/1129
- [x] Depends on
https://chromium-review.googlesource.com/c/v8/v8/+/4036884
- [x] Disable in async ops
- [x] Make it work with owned `String` with an extra alloc in fast path.
- [x] Support `Cow<'_, str>`. Owned for slow case, Borrowed for fast
case
```rust
#[op]
fn op_string_len(s: &str) -> u32 {
str.len() as u32
}
```
This PR introduces Wasm ops. These calls are optimized for entry from
Wasm land.
The `#[op(wasm)]` attribute is opt-in.
Last parameter `Option<&mut [u8]>` is the memory slice of the Wasm
module *when entered from a Fast API call*. Otherwise, the user is
expected to implement logic to obtain the memory if `None`
```rust
#[op(wasm)]
pub fn op_args_get(
offset: i32,
buffer_offset: i32,
memory: Option<&mut [u8]>,
) {
// ...
}
```
Implements fast scheduling of deferred op futures.
```rs
#[op(fast)]
async fn op_read(
state: Rc<RefCell<OpState>>,
rid: ResourceId,
buf: &mut [u8],
) -> Result<u32, Error> {
// ...
}
```
The future is scheduled via a fast API call and polled by the event loop
after being woken up by its waker.
