Resolve a promise using emscripten::val

[Mehdi Sabwat]

Hi,

I have been looking for a way to resolve a Promise using emscripten::val, is that possible? if not, would it be possible in  C/C++ without wrapping it in an EM_ASM?

I have been thinking about Atomics.wait, but I am not sure it is the best way because it is limited to Int32Array. For now, I am using emscripten_async_call(), it would be great if I could replace it with something less hacky.

Thanks

Mehdi

[Brion Vibber]

Are you trying to create a C++ function that schedules work asynchronously and synchronously returns a Promise which can be used by JS code to wait on and retrieve a value?

This should be possible through emscripten::val by translating the equivalent code from JS to val invocations, though I've not tested it... You'd still need to use emscripten_async_call unless there's some other way you intend to schedule the work to happen after the call, such as manual use of setTimeout via val or some other callback.

-- brion

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[Mehdi Sabwat]

I have a JS call that returns a promise. for example :

createAudioFileAsync(audioSettings).then(successCallback);

I don't want to use emscripten_async_call because I don't know when the promise will be resolved.

I tried to val.call<>("then", ...); but I am running into a clang bug.

On Monday, November 25, 2019 at 8:03:41 PM UTC+1, Brion Vibber wrote:

Are you trying to create a C++ function that schedules work asynchronously and synchronously returns a Promise which can be used by JS code to wait on and retrieve a value?

This should be possible through emscripten::val by translating the equivalent code from JS to val invocations, though I've not tested it... You'd still need to use emscripten_async_call unless there's some other way you intend to schedule the work to happen after the call, such as manual use of setTimeout via val or some other callback.

-- brion

On Mon, Nov 25, 2019 at 10:03 AM Mehdi Sabwat <mehdi...@gmail.com> wrote:

Hi,

I have been looking for a way to resolve a Promise using emscripten::val, is that possible? if not, would it be possible in  C/C++ without wrapping it in an EM_ASM?

I have been thinking about Atomics.wait, but I am not sure it is the best way because it is limited to Int32Array. For now, I am using emscripten_async_call(), it would be great if I could replace it with something less hacky.

Thanks

Mehdi

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[Mehdi Sabwat]

I think I solved my issue : (based on [this](https://github.com/RagulanDev/QFace/blob/665add980903374f3e174bc9a17d560890586ed1/src/cpp/main.cpp))

// I can get result["whatever"], or add parameters, depending on the expected callback
void print(val result)
{
  std::cout << "Hi there..." << "\n";
}

int main()
{
  val prom
  promise.call<void>("then", val::module_property("Zecallback"));
  return 0;
}
EMSCRIPTEN_BINDINGS(name) {
  function("Zecallback", &print);
}

couldn't reproduce the bug though, will post it when it pops back.