[Twisted-Python] Twisted tips for designing highly concurrent twisted REST API

[Waqar Khan]

Sorry I had a typo in twisted program

@defer.inlinecallbacks

def long_computation(rec_type, data):
     # some long computation
     *defer.returnValue(recs)*

@defer.inlinecallbacks
def fetch_data(user_id):
        r = yieldjson.loads(requests.get('url/to/fetch/%s'%user_id).text)
     defer.returnValue(r)


@defer.inlinecallbacks
def fetch_recs(user_id):
       data = yield fetch_data(user_id)
        recs = {}
       for stype in similar_types:
            *d = defer.ToThread(long_computation, *(stype, data)) // typo
was here*
           rec = yield d
           recs[stype] = rec
     defer.returnValue(recs)


On Tue, Jun 25, 2019 at 11:48 PM Waqar Khan <wk80333 at gmail.com> wrote:

> Hello folks,
>   I recently stumbled upon twisted and was wondering if it could suit my
> needs. On one hand, I want to use python but on another hand there are all
> these scalability concerns with this language so, I though I would pick the
> brains of the community. So.. a flask based app would look something like
> this.
>
> similar_types = ['foo', 'bar', 'baz']
>
>
> def long_computation(rec_type):
>      # some long computation
>      return recs
>
> @app.route('/fetch_similar_users/<user_id>'
> def fetch_similar_users(user_id)
>         r = json.loads(requests.get('url/to/fetch/%s'%user_id).text)
>         recs = {}
>         for stype in similar_types:
>              recs[stype] = long_computation(rec_type)
>        return recs
>
>
>
> Now, I tried to "twistify" but it failed.
>
> @defer.inlinecallbacks
>
> def long_computation(rec_type):
>      # some long computation
>      *defer.returnValue(recs)*
>
> @defer.inlinecallbacks
> def fetch_data(user_id):
>         r = yieldjson.loads(requests.get('url/to/fetch/%s'%user_id).text)
>      defer.returnValue(r)
>
>
> @defer.inlinecallbacks
> def fetch_recs(user_id):
>        data = yield fetch_data(user_id)
>         recs = {}
>        for stype in similar_types:
>             d = defer.ToThread(fetch_data, *(stype))
>            rec = yield d
>            recs[stype] = rec
>      defer.returnValue(recs)
>
>
>
> I wrapped all the above in twisted render_Get method.. but then I did a
> load test with locust (
> https://docs.locust.io/en/latest/what-is-locust.html) framework.
> It choked. As the time progressed, the response time increased.
> I am guessing, things are still blocking.
>
> Can you please help me look into the right place. Why exactly am I seeing
> increase in response time as the time progresses. I am guessing things are
> still working in "blocking" fashion but i thought the above should run
> things in async.
> Thanks
>
>
>
>
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