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denoland-deno/core/examples/wasm.rs
Matt Mastracci a1764f7690
refactor(core): Improve ergonomics of managing ASCII strings (#18498)
This is a follow-on to the earlier work in reducing string copies,
mainly focused on ensuring that ASCII strings are easy to provide to the
JS runtime.

While we are replacing a 16-byte reference in a number of places with a
24-byte structure (measured via `std::mem::size_of`), the reduction in
copies wins out over the additional size of the arguments passed into
functions.

Benchmarking shows approximately the same if not slightly less wallclock
time/instructions retired, but I believe this continues to open up
further refactoring opportunities.
2023-04-04 06:46:31 -06:00

67 lines
1.9 KiB
Rust

// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
use deno_core::op;
use deno_core::Extension;
use deno_core::JsRuntime;
use deno_core::RuntimeOptions;
use std::mem::transmute;
use std::ptr::NonNull;
// This is a hack to make the `#[op]` macro work with
// deno_core examples.
// You can remove this:
use deno_core::*;
struct WasmMemory(NonNull<v8::WasmMemoryObject>);
fn wasm_memory_unchecked(state: &mut OpState) -> &mut [u8] {
let WasmMemory(global) = state.borrow::<WasmMemory>();
// SAFETY: `v8::Local` is always non-null pointer; the `HandleScope` is
// already on the stack, but we don't have access to it.
let memory_object = unsafe {
transmute::<NonNull<v8::WasmMemoryObject>, v8::Local<v8::WasmMemoryObject>>(
*global,
)
};
let backing_store = memory_object.buffer().get_backing_store();
let ptr = backing_store.data().unwrap().as_ptr() as *mut u8;
let len = backing_store.byte_length();
// SAFETY: `ptr` is a valid pointer to `len` bytes.
unsafe { std::slice::from_raw_parts_mut(ptr, len) }
}
#[op(wasm)]
fn op_wasm(state: &mut OpState, memory: Option<&mut [u8]>) {
let memory = memory.unwrap_or_else(|| wasm_memory_unchecked(state));
memory[0] = 69;
}
#[op(v8)]
fn op_set_wasm_mem(
scope: &mut v8::HandleScope,
state: &mut OpState,
memory: serde_v8::Value,
) {
let memory =
v8::Local::<v8::WasmMemoryObject>::try_from(memory.v8_value).unwrap();
let global = v8::Global::new(scope, memory);
state.put(WasmMemory(global.into_raw()));
}
fn main() {
// Build a deno_core::Extension providing custom ops
let ext = Extension::builder("my_ext")
.ops(vec![op_wasm::decl(), op_set_wasm_mem::decl()])
.build();
// Initialize a runtime instance
let mut runtime = JsRuntime::new(RuntimeOptions {
extensions: vec![ext],
..Default::default()
});
runtime
.execute_script("<usage>", include_ascii_string!("wasm.js"))
.unwrap();
}