Nodehun Promise Example

Setup

yarn install
node index.js

Test

http://localhost:8111/spelling?utterance=%22what%20is%20goinng%20on%22

You will see the console.log from the spellSuggest callback immediately in the terminal.

However the Promise.all() is not fulfilled until a long time. Maybe 30 seconds to over a minute.

Eventually you will see Are we here yet? logged in the terminal and the response completed.

Next: Comment out the return reject and the return resolve lines in spellSuggestPromise

Uncomment out the return setImmediate lines.

So it looks like this ->

function spellSuggestPromise(utterance) {
    return new Promise(function(resolve, reject) {
        dict.spellSuggest(utterance, function(err, correct, suggestion, origWord) {
            console.log(err, correct, suggestion, origWord);
            if (err) {
                return setImmediate(reject, error);
                // return reject(error);
            }
            if (suggestion) {
                // return resolve(suggestion);
                return setImmediate(resolve, suggestion);
            }
            // return resolve(origWord);
            return setImmediate(resolve, origWord);
        });
    });
}

Now kill the server, start it again, and then hit the url again.

You will see the console.log immediately, and Are we here yet? as well. Functions as expected.

Problem?

I think the issue is here https://github.com/Wulf/nodehun/blob/master/src/post0.12.0/nodehun.cpp#L253

at the end of the void Nodehun::SpellDictionary::spellSuggest(const FunctionCallbackInfo<Value>& args) function

uv_queue_work(uv_default_loop(), &spellData->request,
    Nodehun::SpellDictionary::checkSuggestions, Nodehun::SpellDictionary::sendSuggestions);

Looking at http://docs.libuv.org/en/v1.x/threadpool.html

uv_work_cb is set to checkSuggestions, and then uv_after_work_cb is set to sendSuggestions

I'm not sure if this is it exactly, but I'm thinking the that since uv_after_work_cb is called after the threadpool is completed... it may cause the resolves() in the promise to be lost somehow... Although I can't say why they eventually get called... My guess is they're not marked at the end of a runloop, and the loop is waiting for events.. eventually the runloop fires and we get the response

So again.. the workaround for now is to use setImmediate:

return setImmediate(resolve, suggestion);

I just want to make sure I'm not missing anything... I'll be testing this under load soon.