fixing wasm that doesn't preserve states · wasmtime

I can't find a Q&A streams so please move this thread to wherever is appropriate!

So lapce uses wasmtime to manage their plugins and this is the function that compiles/starts a wasm app from a wasm file https://github.com/lapce/lapce/pull/2090
however, it had an issue where the wasm blob does not appear to have a persistent state (my plugin, written in rust, had a OnceCell that gets reset with every function call)
so i proposed a fix here https://github.com/lapce/lapce/pull/2090
can someone review the fix and/or the function it self?
I know that the Engine can probably be extracted out into a lazy static or smth like that

Properly instantiate the WASM blob and let it live inside the thread by hbina · Pull Request #2090 · lapce/lapce

Signed-off-by: Hanif Ariffin hanif.ariffin.4326@gmail.com Added an entry to CHANGELOG.md if this change could be valuable to users

Pat Hickey (Feb 01 2023 at 00:15):

I'm not quite sure I understand the problem, but the unit of mutable state for wasmtime is the Store

Pat Hickey (Feb 01 2023 at 00:18):

if you want to persist state, you will need to make an Instance on your Store, then get the handle_rpc func out of that Instance, and then anytime you do handle_rpc.call(&mut store) it will be the same state underneath as the store had at the end of the last call

Hanif Ariffin (Feb 02 2023 at 01:08):

Okay I read up a bit on WASI and the difference was basically that there are 2 types of WASM: Reactor and Command. Before, I was using it as a Command but now that I instantiate it, I should have a Reactor instead. But now I come into the problem of the environment variable not being set?
I have something like this in Lapce

    let wasi = WasiCtxBuilder::new()
        .env("VOLT_OS", std::env::consts::OS)?
        .env("VOLT_ARCH", std::env::consts::ARCH)?
        .env("VOLT_LIBC", volt_libc)?
        .env(
            "VOLT_URI",
            Url::from_directory_path(volt_path)
                .map_err(|_| anyhow!("can't convert folder path to uri"))?
                .as_ref(),
        )?
        .stdin(Box::new(wasi_common::pipe::ReadPipe::from_shared(
            stdin.clone(),
        )))
        .stdout(Box::new(wasi_common::pipe::WritePipe::from_shared(
            stdout.clone(),
        )))
        .stderr(Box::new(wasi_common::pipe::WritePipe::from_shared(
            stderr.clone(),
        )))
        .preopened_dir(
            wasmtime_wasi::Dir::open_ambient_dir(
                volt_path,
                wasmtime_wasi::ambient_authority(),
            )?,
            "/",
        )?
        .build();
    let mut store = wasmtime::Store::new(&engine, wasi);

format!("envs:{:?}", std::env::vars().collect::<Vec<_>>())

Hanif Ariffin (Feb 02 2023 at 01:26):

Env variables are not being passed to WASM · Issue #74 · bytecodealliance/wasmtime-py

I'm not having any success getting environment variables in the WASM environment. My code is below. There is a function written in C compiled to WASM that does a getenv("FOO") which i...

Hanif Ariffin (Feb 02 2023 at 01:40):

so it seems that I should call an exported function called _initialize but its not there? this crashes the thread

let initialize = instance
        .get_typed_func::<(), (), _>(&mut store, "_initialize")
        .unwrap();

bjorn3 (Feb 02 2023 at 09:03):

bjorn3 (Feb 02 2023 at 09:04):

It is possible that somewhere in wasi-libc or rust's libstd some initialization is missed for the reactor case.

Hanif Ariffin (Feb 02 2023 at 11:59):

but i dont have a reactor, i have a command. How do i compile my plugin to make sure that it gets compiled as a reactor? https://github.com/lapce/lapce-rust.git

bjorn3 (Feb 02 2023 at 12:10):

If the plugin is written in rust you can use the unstable -Zwasi-exec-model=reactor. If it is written in C I believe the flag to use is -fexec-model=reactor but I might be wrong about that one.

Stream: wasmtime

Topic: fixing wasm that doesn't preserve states

Hanif Ariffin (Jan 31 2023 at 15:33):