For API consistency reasons, it would be good if we did this holistically
and expanded this approach to state, side outputs, ... so that a person can
always call Something.get() to return something that they can access
implementation wise. It will be confusing for our users to have many
variations in our style of how all these concepts are used (ProcessContext
/ Annotations / #get())
On Tue, Sep 5, 2017 at 8:08 AM, Eugene Kirpichov <
kirpic...@google.com.invalid> wrote:
> Also, I think my approach is compatible with annotations and future removal
> of .withSideInputs if we annotate a field:
> final PCollectionView<Foo> foo = ...;
>
> class MyDoFn {
> @SideInput
> PCollectionView<Foo> foo = foo;
>
> ...foo.get()...
> }
>
> We can extract the accessed views from the DoFn instance using reflection.
> Still not compatible with lambdas, but compatible automatically with all
> anonymous classes.
>
> On Tue, Sep 5, 2017, 8:02 AM Eugene Kirpichov <kirpic...@google.com>
> wrote:
>
> > Hi Luke,
> >
> > I know this (annotations) is the pattern we were considering for side
> > inputs, but I no longer think it is the best way to access them.
> > Annotations help getting rid of the .withSideInputs() call, but this is
> > where their advantage ends.
> >
> > The advantages of the proposed approach are that it automatically works
> > with all existing callback or lambda code. No need to further develop the
> > reflection machinery to support side input annotations - and especially
> to
> > support arbitrary user interfaces, no need to change existing transforms,
> > no need for transform authors to even know that the machinery exists to
> > make side inputs usable in their transforms (and no need for authors to
> > think about whether or not they should support side inputs).
> >
> > Moreover, like Reuven says, annotations don't work with lambdas at all:
> > creating a lambda with a flexible set of annotation arguments appears to
> be
> > currently impossible, and even capturing the annotations on arguments of
> a
> > lambda is I believe also impossible because the Java compiler drops them
> in
> > the generated class or method handle.
> >
> > On Tue, Sep 5, 2017 at 6:57 AM Lukasz Cwik <lc...@google.com.invalid>
> > wrote:
> >
> >> I believe we should follow the pattern that state uses and add a type
> >> annotation to link the side input definition to its usage directly. This
> >> would allow us to know that the side input was definitely being accessed
> >> and perform validation during graph construction for any used but
> >> unspecified side inputs.
> >>
> >> Code snippet:
> >> final PCollectionView<String> foo = pipeline.apply("fooName",
> >> Create.of("foo")).apply(View.<String>asSingleton());
> >> PCollection<String> output = pipeline
> >> .apply(Create.of(1, 2, 3))
> >> .apply(MapElements.via(
> >> new SimpleFunction<Integer, String>() {
> >> @Override
> >> public String apply(Integer input, @SideInput("fooName")
> String
> >> fooValue) {
> >> return fooValue + " " + input;
> >> }
> >> }).withSideInputs(foo));*
> >>
> >> On Mon, Sep 4, 2017 at 6:22 PM, Eugene Kirpichov <
> >> kirpic...@google.com.invalid> wrote:
> >>
> >> > Sure, here's how a modified (passing) MapElements unit test looks
> like,
> >> > with usage of side inputs:
> >> >
> >> > @Test
> >> > @Category(NeedsRunner.class)
> >> > public void testMapBasicWithSideInput() throws Exception {
> >> > * final PCollectionView<String> foo =*
> >> > * pipeline.apply("foo",
> >> > Create.of("foo")).apply(View.<String>asSingleton());*
> >> > PCollection<String> output = pipeline
> >> > .apply(Create.of(1, 2, 3))
> >> > .apply(MapElements.via(
> >> > new SimpleFunction<Integer, String>() {
> >> > @Override
> >> > public String apply(Integer input) {
> >> > return* foo.get() *+ " " + input;
> >> > }
> >> > })
> >> > *.withSideInputs(foo));*
> >> >
> >> > PAssert.that(output).containsInAnyOrder("foo 1", "foo 2", "foo
> 3");
> >> > pipeline.run();
> >> > }
> >> >
> >> >
> >> > On Mon, Sep 4, 2017 at 6:12 PM Reuven Lax <re...@google.com.invalid>
> >> > wrote:
> >> >
> >> > > Can you provide a code snippet showing how this would look?
> >> > >
> >> > > On Sun, Sep 3, 2017 at 6:49 PM, Eugene Kirpichov <
> >> > > kirpic...@google.com.invalid> wrote:
> >> > >
> >> > > > TL;DR Introduce method PCollectionView.get(), implemented as: get
> >> > > > thread-local ProcessContext and do c.sideInput(this). As a result,
> >> any
> >> > > user
> >> > > > lambdas such as MapElements can use side inputs.
> >> > > >
> >> > > > Quite a few transforms have user-code callbacks or lambdas: ParDo
> >> > (DoFn),
> >> > > > Map/FlatMapElements, the DynamicDestinations classes in various
> IOs,
> >> > > > combine fns, the PollFn callback in Watch, etc.
> >> > > >
> >> > > > Of these, only DoFn and CombineFn have built-in support for side
> >> > inputs;
> >> > > > for DynamicDestinations it is plumbed explicitly; others don't
> have
> >> > > access
> >> > > > (e.g. you can't access side inputs from Map/FlatMapElements
> because
> >> > they
> >> > > > don't have a ProcessContext or any context for that matter).
> >> > > >
> >> > > > I think it's important to solve this, especially as Java 8 becomes
> >> > > people's
> >> > > > default choice: users will want to use side inputs in
> >> > > Map/FlatMapElements.
> >> > > >
> >> > > > It also appears to be quite easy to implement:
> >> > > >
> >> > > > Runner part:
> >> > > > - introduce a SideInputAccessor interface
> >> > > > - make .get() on a PCollectionView get it from a thread-local
> >> > > > SideInputAccessor
> >> > > > - make runners set the thread-local SideInputAccessor any time the
> >> > runner
> >> > > > is evaluating something in a context where side inputs are
> >> available,
> >> > > e.g.
> >> > > > a ProcessElement method, or applying a CombineFn - the set of such
> >> > places
> >> > > > will be quite small. I believe only runners (but not transforms)
> >> will
> >> > > ever
> >> > > > need to set this thread-local
> >> > > >
> >> > > > Transform part:
> >> > > > - Transforms that take user-code lambdas and want to let them
> access
> >> > side
> >> > > > inputs still will need to be configurable with a method like
> >> > > > .withSideInputs(view1, view2...) and will need to plumb those down
> >> to
> >> > the
> >> > > > primitive DoFn's or CombineFn's - information on *which* side
> inputs
> >> > will
> >> > > > be accessed, of course, still needs to be in the graph.
> >> > > >
> >> > > > I quickly prototyped this in direct runner and MapElements, and it
> >> > worked
> >> > > > with no issues - I'm wondering if there's something subtle that
> I'm
> >> > > > missing, or is it actually a good idea?
> >> > > >
> >> > >
> >> >
> >>
> >
>
