Re: [tarantool-patches] Re: [PATCH 6/8] netbox: introduce fiber-async API

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Mon, Apr 23, 2018 at 09:59:29PM +0300, Vladislav Shpilevoy wrote:
> Hello. Thanks for review!
> 
> On 23/04/2018 19:44, Vladimir Davydov wrote:
> > On Mon, Apr 16, 2018 at 09:39:16PM +0300, Vladislav Shpilevoy wrote:
> > > Now any netbox call blocks a caller-fiber until a result is read
> > > from a socket, or time is out. To use it asynchronously it is
> > > necessary to create a fiber per request. Sometimes it is
> > > unwanted - for example if RPS is very high (for example, about
> > > 100k), and latency is about 1 second. Or when it is neccessary
> > > to send multiple requests in paralles and then collect responses
> > > (map-reduce).
> > > 
> > > The patch introduces a new option for all netbox requests:
> > > is_async. With this option any called netbox method returns
> > > immediately (but still yields for a moment) a 'future' object.
> > > 
> > > By a future object a user can check if the request is finalized,
> > > get a result or error, wait for a timeout, discard a response.
> > > 
> > > Example of is_async usage:
> > > future = conn:call(func, {params}, {..., is_async = true})
> > > -- Do some work ...
> > > if not future.is_ready() then
> > >      result, err = future:wait_result(timeout)
> > > end
> > > -- Or:
> > > result, error = future:result()
> > > 
> > > A future:result() and :wait_result() returns either an error or
> > > a response in the same format, as the sync versions of the called
> > > methods.
> > > 
> > > Part of #3107
> > > +            -- It is possible that multiple fibers are waiting for
> > > +            -- a result. In such a case a first, who got it, must
> > > +            -- wakeup the previous waiting client. This one wakes
> > > +            -- up another. Another wakes up third one, etc.
> > > +            wakeup_client(old_client)
> > 
> > This is rather difficult for understanding IMO. Can we use a fiber.cond
> > instead?
> 
> Sure, we can. Done on the branch.

Thanks. The patch looks good to me now.