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DDeno

•Created by erksch on 9/23/2024 in #help

RustyV8: Example of using PromiseResolver / async?

but the External and the Function is created on a scope that is destroyed

16 replies

DDeno

•Created by erksch on 9/23/2024 in #help

RustyV8: Example of using PromiseResolver / async?

Oh sorry, yes of course, the promise is the result 🙂

16 replies

DDeno

•Created by erksch on 9/23/2024 in #help

RustyV8: Example of using PromiseResolver / async?

@bartlomieju Oh, very nice, that makes sense. Thanks a lot!

let data = PromiseThenCallbackData {
    sender: received.1,
    promise: v8::Global::new(scope, promise),
};

let data = PromiseThenCallbackData {
    sender: received.1,
    promise: v8::Global::new(scope, promise),
};

I was thinking that the result of the js call would be saved to the scope, which would be released before the callback is executed, so that I would need to run it in a special callbackscope that is then destroyed with the callback, but apparently this works.

16 replies

DDeno

•Created by erksch on 9/23/2024 in #help

RustyV8: Example of using PromiseResolver / async?

The callback looks like this:

fn promise_then_callback(
  scope: &mut HandleScope<'_>,
  args: v8::FunctionCallbackArguments<'_>,
  _: v8::ReturnValue<'_>,
) 
{
  let cvoid = args.data().cast::<v8::External>().value();
  let data = helper::cvoid_to_type::<PromiseThenCallbackData>(cvoid);
  let data = unsafe { Box::from_raw(data) };

  match data.promise.state() {
      PromiseState::Pending => {
          exit(1); //TODO
      }
      PromiseState::Fulfilled => {
          let result = data.promise.result(scope);
          let number: f64 = v8::Local::<v8::Number>::try_from(result)
              .ok()
              .unwrap()
              .value();
          data.sender.send(Ok(Box::new(number))).unwrap();
      }
      PromiseState::Rejected => {
          exit(1); //TODO
      }
}

fn promise_then_callback(
  scope: &mut HandleScope<'_>,
  args: v8::FunctionCallbackArguments<'_>,
  _: v8::ReturnValue<'_>,
) 
{
  let cvoid = args.data().cast::<v8::External>().value();
  let data = helper::cvoid_to_type::<PromiseThenCallbackData>(cvoid);
  let data = unsafe { Box::from_raw(data) };

  match data.promise.state() {
      PromiseState::Pending => {
          exit(1); //TODO
      }
      PromiseState::Fulfilled => {
          let result = data.promise.result(scope);
          let number: f64 = v8::Local::<v8::Number>::try_from(result)
              .ok()
              .unwrap()
              .value();
          data.sender.send(Ok(Box::new(number))).unwrap();
      }
      PromiseState::Rejected => {
          exit(1); //TODO
      }
}

16 replies

DDeno

•Created by erksch on 9/23/2024 in #help

RustyV8: Example of using PromiseResolver / async?

@bartlomieju When I call a JS function that returns a promise, polling if the promise has finished is expensive. So I implemented a callback on .then, but it needs both the promise and the oneshot sender, so I'm embedding it as data:

let promise = js_test_async.call(scope, global.into(), &[]).unwrap().cast::<v8::Promise>();
let data = PromiseThenCallbackData {
    sender: x.1,
    promise,
};
let data_box: *mut T = Box::leak(Box::new(typed_data));
let cvoid = data_box as *mut c_void;
let data_external = v8::External::new(scope, cvoid);
let f = v8::FunctionBuilder::<v8::Function>::new(promise_then_callback)
    .data(data_external.into())
    .build(scope)
    .unwrap();
promise.then(scope, f);

let promise = js_test_async.call(scope, global.into(), &[]).unwrap().cast::<v8::Promise>();
let data = PromiseThenCallbackData {
    sender: x.1,
    promise,
};
let data_box: *mut T = Box::leak(Box::new(typed_data));
let cvoid = data_box as *mut c_void;
let data_external = v8::External::new(scope, cvoid);
let f = v8::FunctionBuilder::<v8::Function>::new(promise_then_callback)
    .data(data_external.into())
    .build(scope)
    .unwrap();
promise.then(scope, f);

Unfortunately this either causes a 1) use-after-free, if I create a short-lived scope (callback outlives it) 2) memory leak I tried to use CallbackScope but that isnt accepted as a scope arg. What's the right approach? Basically I want all of the above to get dropped only when the callback has finished.

16 replies

DDeno

•Created by erksch on 9/23/2024 in #help

RustyV8: Example of using PromiseResolver / async?

@bartlomieju I managed to get it all to work, but it was quite a fight 🫠
I did manage to implement bidirectional async without MaskFutureAsSend, so that's something 🥂 Can I get back to you if I face another blocking issue? I realize this is a Deno support forum and not really for RustyV8 🙂

16 replies

DDeno

•Created by erksch on 9/22/2024 in #help

Embedding RustyV8: Fatal JavaScript out of memory: Reached heap limit

Indeed that solved the issue.

c.bench_function("v8 json deserialize", |b| {
        b.iter(|| {
            let scope = &mut HandleScope::new(scope);
            let json_str = r#"{"key": "value", "number": 42}"#;
            let json_v8_str = v8::String::new(scope, json_str).unwrap();
            let _json_obj = v8::json::parse(scope, json_v8_str).unwrap();
        })
    });

c.bench_function("v8 json deserialize", |b| {
        b.iter(|| {
            let scope = &mut HandleScope::new(scope);
            let json_str = r#"{"key": "value", "number": 42}"#;
            let json_v8_str = v8::String::new(scope, json_str).unwrap();
            let _json_obj = v8::json::parse(scope, json_v8_str).unwrap();
        })
    });

@bartlomieju I was thinking about implementing a custom deserializer (e.g. from bincode), and did a trivial benchmark of String::new, but it seems rather slow? I assume the V8 deserializer has a more direct/lowlevel approach? Would it be feasible to do in Rust using the RustyV8 bindings?

c.bench_function("v8 1k string new", |b| {
        let json_str = r#"{"key": "value", "number": 42}"#;
        b.iter(|| {
            let scope = &mut HandleScope::new(scope);
            for _ in 0..1000 {
                black_box(v8::String::new(scope, json_str).unwrap());
            }
        })
    });

c.bench_function("v8 1k string new", |b| {
        let json_str = r#"{"key": "value", "number": 42}"#;
        b.iter(|| {
            let scope = &mut HandleScope::new(scope);
            for _ in 0..1000 {
                black_box(v8::String::new(scope, json_str).unwrap());
            }
        })
    });

4 replies