Simran-B
commented
5 years ago Going from WebAssembly to something else like JavaScript is not a common use case and not what WebAssembly is about. It "is a binary instruction format [...]. Wasm is designed as a portable target for compilation of high-level languages like C/C++/Rust" (source).
So you write code in e.g. Rust, compile it to .wasm (bytecode) and can use it in browsers or Node.js. There is no parsing like with text-based JavaScript code (which is kinda slow), but there is still some decoding to do to make it run on your machine (pretty fast). This is intended: WebAssembly is supposed to be portable, which means you can't compile it to machine code to run directly, because then it would be limited to a particular computer architecture it can run on.
There is actually a tool called wasm2c which can transpile .wasm to C code, which you could then compile natively. But then you're outside the web platform. And if your code was written in e.g. Rust, then it would be by far easier to compile from Rust to native code directly.
To the actual question: ArangoDB 3.2-3.4 embed V8 in version 5.7.492.77. Based on a post on StackOverflow, this is apparently one of the first versions that supports WebAssembly. I conducted a little test and got something working. So generally speaking, it is possible. However, you should be careful as this feature isn't tested so far, expect there to be a cost for calls and data transfer between JS <-> WASM and keep in mind that V8 features for WebAssembly like streamed compilation and recent optimizations (e.g. Liftoff) are not in ArangoDB at this point in time. A future version may come with a newer V8 version though.
If you look for a way to do heavy computation in ArangoDB with as little overhead as possible, then you should probably implement the required code in C++ and compile everything from source. There you have ways to run computations in multiple threads etc., whereas Foxx doesn't support the child_process module, WebAssembly Threads v1 has no native threads in the specs and a preview is only available in V8 7.0 anyway.
I loosely followed a Rust and WebAssembly tutorial to set up the necessary tools to create a wasm module. It exports a single function which takes two integers, adds them up and returns the result as integer:
src/lib.rs
// ...
#[wasm_bindgen]
pub fn calc(a: i32, b: i32) -> i32 {
return a + b;
}I used wasm-pack build --target nodejs to build the module. It resulted in a 601 bytes .wasm file. There will be a *_bg.js file which contains the glue code to load and instantiate the module, but I had to change it a little to make it work:
_pkg/wasm_foxx_testbg.js
const path = require('path').join(__dirname, 'wasm_foxx_test_bg.wasm');
const bytes = require('fs').readFileSync(path);
let imports = {};
const wasmModule = new WebAssembly.Module(new Uint8Array(bytes)); // edited
const wasmInstance = new WebAssembly.Instance(wasmModule, imports);
module.exports = wasmInstance.exports;Without new Uint8Array(...) I got the following error, even though bytes is a Buffer:
TypeError: WebAssembly.Module(): Argument 0 must be a buffer source
index.js (_pkg/wasm_foxx_testbg.js copied as index.js into new folder _/wasm_foxxtest in Foxx source root, together with the file _/pkg/wasm_foxx_testbg.wasm)
'use strict';
const createRouter = require("@arangodb/foxx/router");
const joi = require('joi');
const wasm = require("./wasm_foxx_test");
const router = createRouter();
router.get('/:x/:y', function (req, res) {
res.send(wasm.calc(req.pathParams.x, req.pathParams.y));
})
.pathParam('x', joi.number())
.pathParam('y', joi.number())
.response(joi.number().integer(), 'An integer')
.summary('Return externally calculated integer')
.description('Calls WebAssembly function to add up two integers');
module.context.use(router);I used foxx install /calc-service (Foxx-CLI) to deploy the service.
URL to test the service: http://localhost:8529/_db/_system/calc-service/4/7.8
It displays 11. Note how 7.8 is truncated to 7 because calc() is defined for integers in the Rust code.
mpoeter
TZubiri
If so must they be compiled to javascript first? Or can wasm be compiled to bytecode? Are there any examples?
Thank you!