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From YiZhi Liu <eazhi....@gmail.com>
Subject Re: Feedback request for new Java API
Date Sat, 29 Sep 2018 19:37:26 GMT
Some of my comments inline:

> Why can we not create the builder just for these APIs( which we discussed), why is it
necessary to add 200 Apis
It is about unified user-experience. And we get rid of annoying extra
"out=null" in every operator.

> Are you suggesting to create builder for each and every API?
Only for those are necessary. For NDArray.XXX, yes.

1) The NDArray APIs in question are not following functional style of
programming, in fact they are just static methods defined on an
NDArray object - so Scala users are not losing much by using null in
place of None.
You can create a implicit to maintain backward compatibility
- I doubt implicit can work in such case from None -> null.

2) It is adding 220+ APIs(I understand it is generated) for NDArray alone
- As I explained how it can improve user experiences

3) this is adding another 100s of APIs unnecessarily, we are starting with
NDArray but we can't stop there, we will have to do this for Symbol,
Executor, Iterators, etc., .
- This is a good point, actually I prefer not to make JavaExecutor,
JavaIterators

4) I don't want to be fixing bugs and maintaining code in 2 places.
- Type-safe parsing is shared. I think Qing is more qualified to comment.

5) I want the cryptic code(# scala macros) to a minimum.
- MXNet decides to do operator generation in frontend bindings. It's
the developers' responsibility to understand the techniques they are
using. Maybe not a so proper analogy - "I don't know RL / RL is hard
to tune / ..." is not a reason for "I want to keep RL implementation
in MXNet as a small part as possible"

6) increased compilation time & bad developer experience - the time to
compile has gone up quite a bit since we added the APIs last release on my
3 year old laptop already.. I think adding 400+ APIs unnecessarily would
significantly increase build time and bad developer experience
- I don't think increasing such a bit compilation time is a problem
compared to bad user experience.

7) I want to keep the core of the framework to be in Scala - because it
allows you to write concise code - Yes it has a bit of learning curve, not
everyone needs to know. I would rather invest in solidifying the Scala APIs
and add more features in Scala(RNN, Support GluonHybridizedBlock...there is
quite bit of work ) - do you want to rewrite everything in Scala and Java.
- I agree with "don't rewrite everything in Scala and Java", IMO
JavaNDArray is the only one good to have. JShape, JContext, etc. are
not so necessary.

8) Also, the discussion is not creating NDArray class for Java, just
generate certain APIs to cater for Java incompatibility.
- Yes I agree it's about "generate certain APIs to cater for Java
incompatibility", though I think NDArray.api.XXX does not meet Java
users' demands.
On Sat, Sep 29, 2018 at 12:05 PM Naveen Swamy <mnnaveen@gmail.com> wrote:
>
> I know it is about trade-off.  I am suggesting a trade-off , how many apis do we have
that takes too many parameters ?
> From what I recall its around 20. Why can we not create the builder just for these APIs(
which we discussed), why is it necessary to add 200 Apis ?
> Are you suggesting to create builder for each and every API?
>
> I disagree with your opinion that they are not important and would like to hear from
others.
>
> I am curious to see how the #2 looks like compared to #1
> Andrew/Qing, can you paste the generated Apis that you have for both Scala and Java in
a gist please.
>
> > On Sep 29, 2018, at 2:41 PM, YiZhi Liu <eazhi.liu@gmail.com> wrote:
> >
> > Naveen, software designing is all about tradeoff, every feature we
> > introduce causes more compiling time, more efforts to maintain, etc.
> >
> > The main difference is.
> >
> > Option #1: Java users do
> > NDArray.BatchNorm(data, gamma, beta, null, null, null, null, null,
> > null, null, null, null, null, null);
> > (and because every operator has an argument "out", users need to add
> > an extra "null" to the function call almost every time.)
> >
> > Option #2, Java users do
> > JavaNDArray.BatchNorm(data).setGamma(gamma).setBeta(beta).invoke();
> >
> > I don't think any of the reasons you listed is so important as the
> > benefit above we got from option #2.
> >> On Sat, Sep 29, 2018 at 8:24 AM Naveen Swamy <mnnaveen@gmail.com> wrote:
> >>
> >> Java APIs are not like Clojure - The current proposal is only to build a
> >> few thin wrappers for Inference.
> >>
> >> To better represent the two cases and this discussion in particular, here
> >> is an example API
> >>
> >> 1) def Activation (data : org.apache.mxnet.NDArray, act_type : String, out
> >> : Option[NDArray] = None) : org.apache.mxnet.NDArrayFuncReturn
> >> or
> >> 2) def Activation (data : org.apache.mxnet.NDArray, act_type : String, out
> >> : NDArray) : org.apache.mxnet.NDArrayFuncReturn
> >>
> >> The discussion is should we add(generate) 200+ APIs to make it Java
> >> compatible, ie., remove the Option class and the None default value which
> >> Java does not understand from Option 1)
> >>
> >> my suggestion was to remove the Option class and create a implicit for
> >> backward compatibility and use null instead of None, Andrew and I disagreed
> >> on this, so I suggested to raise a discussion on dev@ to get more opinions
> >> and one of us will disagree and commit. Thanks for raising it :)
> >>
> >> | * def Activation (data : org.apache.mxnet.NDArray, act_type : String, out
> >> : NDArray = null) : org.apache.mxnet.NDArrayFuncReturn |
> >> --
> >>
> >> 1) It is not true that Scala users will lose *default/optional* arguments -
> >> if we followed the above, they will use null or None, though I do not like
> >> using nulls, this is a fine compromise.
> >> To keep backward compatibility we can create a implicit to convert
> >> Option.None to nulls and Option.Some-> Option.get(), so you are not going
> >> to break users who might have been using the APIs that were released in
> >> 1.3. The current incompatibility is only this w.r.t. NDArrays.
> >>
> >> 2) Now about the Scala Macros - they are not simple to read or use, When I
> >> and Qing started working on the #Scala Macros to improve the APIs, it took
> >> us a good amount of time to get a hang of it. I don't want to add
> >> additional code when not necessary.
> >>
> >> My suggestion and vote is to modify existing Macro(i.e., #1 from the
> >> original email with the necessary clarification above) and make it
> >> compatible with Java
> >> Here are my reasons
> >> 1) The NDArray APIs in question are not following functional style of
> >> programming, in fact they are just static methods defined on an NDArray
> >> object - so Scala users are not losing much by using null in place of None.
> >> You can create a implicit to maintain backward compatibility
> >> 2) It is adding 220+ APIs(I understand it is generated) for NDArray alone
> >> 3) this is adding another 100s of APIs unnecessarily, we are starting with
> >> NDArray but we can't stop there, we will have to do this for Symbol,
> >> Executor, Iterators, etc., .
> >> 3) I don't want to be fixing bugs and maintaining code in 2 places.
> >> 4) I want the cryptic code(# scala macros) to a minimum.
> >> 5) increased compilation time & bad developer experience - the time to
> >> compile has gone up quite a bit since we added the APIs last release on my
> >> 3 year old laptop already.. I think adding 400+ APIs unnecessarily would
> >> significantly increase build time and bad developer experience
> >> 6) I want to keep the core of the framework to be in Scala - because it
> >> allows you to write concise code - Yes it has a bit of learning curve, not
> >> everyone needs to know. I would rather invest in solidifying the Scala APIs
> >> and add more features in Scala(RNN, Support GluonHybridizedBlock...there is
> >> quite bit of work ) - do you want to rewrite everything in Scala and Java.
> >> 7) Also, the discussion is not creating NDArray class for Java, just
> >> generate certain APIs to cater for Java incompatibility.
> >>
> >> @Andrew: To your response to Qing's comments - you cannot just consider it
> >> as just generating NDArray's APIs and instead I suggest to take a wholistic
> >> view of all the various implications.
> >>
> >> @Chris: Yes, Scala has a bit of learning curve - the goal is not having
> >> every developer to deal with how these APIs are generated,
> >> the problem exists either ways with the above proposal. I might agree if we
> >> were to move away completely(with a thorough discussion and valid reasons)
> >> and instead use AspectJ or similar to write these APIs, the discussion is
> >> about using Scala Macros to generate 2 different types of APIs which are
> >> functionally not different and usability wise are very very similar, look
> >> at the example.
> >> Thanks for your input, I will deposit your 0.02$ in our JIRA bank :)
> >>
> >> @Carin: It requires more effort to use AspectJ or similar to generate APIs
> >> using reflection or at compile time, here we need to generate at compile
> >> time so Java users have the API signature on their IDEs.
> >>
> >> Thanks, Naveen
> >>
> >> P.S: I am traveling and my responses will be delayed.
> >>
> >>
> >>> On Fri, Sep 28, 2018 at 10:25 AM Carin Meier <carinmeier@gmail.com>
wrote:
> >>>
> >>> Sorry bad paste on the gist - here is the good one
> >>> https://gist.github.com/gigasquid/01cd48f563db4739910592dd9ac9db20
> >>>
> >>>> On Fri, Sep 28, 2018 at 10:24 AM Carin Meier <carinmeier@gmail.com>
wrote:
> >>>>
> >>>> +1 on option #2
> >>>>
> >>>> In the case of minimizing the the overhead for code maintenance, I wanted
> >>>> to suggest the option of investigating generating code from the Java
> >>>> Reflection for the Java APIs.  I did a quick gist from Clojure of what
> >>> the
> >>>> generated classes look like from the current Scala Symbol.api for
> >>>> FullyConnected here
> >>>> https://gist.github.com/gigasquid/01cd48f563db4739910592
> >>>>
> >>>> I looks like that there is always a base Java class generated will all
> >>> the
> >>>> arguments. If this is the case, then there is a possibility to generate
a
> >>>> Java api based on this Java method automatically with just a conversion
> >>> for
> >>>> the Scala option and it might be reusable for all the packages.
> >>>>
> >>>> Not sure if it will work for this use case, but thought I would bring
it
> >>>> up in case it's helpful.
> >>>>
> >>>> - Carin
> >>>>
> >>>> On Fri, Sep 28, 2018 at 7:05 AM Davydenko, Denis <dden@amazon.com.invalid
> >>>>
> >>>> wrote:
> >>>>
> >>>>> +1 on option #2. Having clear Java interface for NDArray, from my
> >>>>> perspective, would be a better experience for Java users as it won't
> >>>>> require them to deal with Scala code in any capacity. Overhead of
extra
> >>>>> code for additional macros is justified, in my mind, as it will
be
> >>>>> introduced with option #1 either way, just in a different place.
> >>>>>
> >>>>> --
> >>>>> Thanks,
> >>>>> Denis
> >>>>>
> >>>>> On 9/27/18, 6:14 PM, "YiZhi Liu" <eazhi.liu@gmail.com>
wrote:
> >>>>>
> >>>>>  I vote for "2.) Leave the existing macro in place and add another
> >>>>>  which generates a Java friendly version"
> >>>>>
> >>>>>  @Qing @Andrew, could you give some examples, so that people can
> >>> better
> >>>>>  understand how it provides "best possible experience" to Java users.
> >>>>>
> >>>>>  I have no strong preference between having JavaShape & JavaContext
> >>> or
> >>>>> not.
> >>>>>  On Thu, Sep 27, 2018 at 5:56 PM Andrew Ayres <
> >>>>> andrew.f.ayres@gmail.com> wrote:
> >>>>>>
> >>>>>> That's not really the conversation I'm wanting to have. I want
a
> >>>>> discussion
> >>>>>> about the macros with respect to NDArray so that we can get
> >>>>> agreement on
> >>>>>> our path forward with respect to implementing the NDArray wrapper.
> >>>>>>
> >>>>>> The design that was put forth and agreed to was for a a Java
> >>>>> wrapper around
> >>>>>> the Scala API. Adding a bunch of Java friendly methods inside
the
> >>>>> Scala
> >>>>>> code would create a mess for users. Maintenance would be
> >>>>> essentially the
> >>>>>> same for both because either way you're going to be updating
Java
> >>>>> methods
> >>>>>> when you make Scala changes.
> >>>>>>
> >>>>>> Let's please stick with the issue in the original email.
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Andrew
> >>>>>>
> >>>>>>> On Thu, Sep 27, 2018 at 5:22 PM Qing Lan <lanking520@live.com>
> >>>>>> wrote:
> >>>>>>
> >>>>>>> I would like to loop this back a layer. Current, there is
a
> >>>>> discussion in
> >>>>>>> the MXNet Scala community on the ways to implement the Java
> >>> APIs.
> >>>>> Currently
> >>>>>>> there are two thoughts:
> >>>>>>>
> >>>>>>> 1. Make Scala Java Friendly (Create Java compatible methods
in
> >>>>> the Scala
> >>>>>>> Class. such as NDArray with Java compatible constructor)
> >>>>>>> 2. Make Java friendly wrappers in Scala (Andrew's explanation
> >>>>> below)
> >>>>>>>
> >>>>>>> The first approach require minimum input from our side to
> >>>>> implement
> >>>>>>> however bring user a bunch of useless api they may not want
to
> >>>>> use. It also
> >>>>>>> makes Scala package heavier. The good thing is these two
> >>> packages
> >>>>> require
> >>>>>>> minimum maintenance cost. As a tradeoff, if any time in
the
> >>>>> future we want
> >>>>>>> to make Java big (make Java as the primary language supported
by
> >>>>> MXNet),
> >>>>>>> then the migration from Scala to Java will be harmful. Spark
> >>>>> consider this
> >>>>>>> carefully and decide not to change much on their Scala code
base
> >>>>> to make it
> >>>>>>> more Java.
> >>>>>>>
> >>>>>>> The second approach will make unique NDArray, Shape, Context
and
> >>>>> more. The
> >>>>>>> good thing about this is we can always holds a version control
> >>> on
> >>>>> Java.
> >>>>>>> Some breaking changes on Scala may not influence much on
Java.
> >>> It
> >>>>> did the
> >>>>>>> best way to decouple the module and good for us to build
unique
> >>>>> pipeline
> >>>>>>> for Java. The bad thing with this design is the maintenance
cost
> >>>>> as we need
> >>>>>>> to keep two code bases, but it also make Java side easy
to
> >>> change
> >>>>> to make
> >>>>>>> it better compatible with users.
> >>>>>>>
> >>>>>>> Thanks,
> >>>>>>> Qing
> >>>>>>>
> >>>>>>> On 9/27/18, 3:25 PM, "Andrew Ayres" <andrew.f.ayres@gmail.com>
> >>>>> wrote:
> >>>>>>>
> >>>>>>>  Hi,
> >>>>>>>
> >>>>>>>  Currently, we're working to implement a new Java API and
> >>>>> would like
> >>>>>>> some
> >>>>>>>  feedback from the community on an implementation detail.
In
> >>>>> short, the
> >>>>>>> new
> >>>>>>>  Java API will use the existing Scala API (in a manner
> >>> similar
> >>>>> to how
> >>>>>>> the
> >>>>>>>  current Clojure API works). This basically means that we're
> >>>>> making Java
> >>>>>>>  friendly wrappers to call the existing Scala API.
> >>>>>>>
> >>>>>>>  The feedback we're looking for is on the implementation
of
> >>>>> NDArray.
> >>>>>>> Scala's
> >>>>>>>  NDArray has a significant amount of code which is generated
> >>>>> via macros
> >>>>>>> and
> >>>>>>>  we've got two viable paths to move forward:
> >>>>>>>
> >>>>>>>  1.) Change the macro to generate Java friendly methods
 - To
> >>>>> do this
> >>>>>>> we'll
> >>>>>>>  modify the macro so that the generated methods won't have
> >>>>>>> default/optional
> >>>>>>>  arguments. There may also have to be some changes to
> >>>>> parameter types to
> >>>>>>>  make them Java friendly. The big advantage here is that
> >>>>> ongoing
> >>>>>>> maintenance
> >>>>>>>  will easier. The disadvantages are that we'll be changing
> >>> the
> >>>>> existing
> >>>>>>>  Scala NDArray Infer API (it's marked experimental) and
Scala
> >>>>> users will
> >>>>>>>  lose the ability to use the default and optional arguments.
> >>>>>>>
> >>>>>>>  2.) Leave the existing macro in place and add another which
> >>>>> generates a
> >>>>>>>  Java friendly version - The biggest issue here is that
we'll
> >>>>> be
> >>>>>>> doubling
> >>>>>>>  the number of macros that we've got to maintain. It'll
> >>> become
> >>>>> even more
> >>>>>>>  overhead once we start expanding the Java API with more
> >>>>> classes that
> >>>>>>> use
> >>>>>>>  generated code like this. The advantages are that the
> >>>>> existing Scala
> >>>>>>>  NDArray Infer API would remain unchanged for Scala users
and
> >>>>> that the
> >>>>>>> new
> >>>>>>>  macro could be optimized to give the best possible
> >>> experience
> >>>>> to the
> >>>>>>> Java
> >>>>>>>  API.
> >>>>>>>
> >>>>>>>  Thanks,
> >>>>>>>  Andrew
> >>>>>
> >>>>>
> >>>>>
> >>>>>  --
> >>>>>  Yizhi Liu
> >>>>>  DMLC member
> >>>>>  Amazon Web Services
> >>>>>  Vancouver, Canada
> >
> >
> >
> > --
> > Yizhi Liu
> > DMLC member
> > Amazon Web Services
> > Vancouver, Canada



-- 
Yizhi Liu
DMLC member
Amazon Web Services
Vancouver, Canada

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