The same goes for a Java or C++ class that changes its api. In general this is left to the developer, and these languages have internals as private by default for precisely the same purpose. The module developer must have the right to change internals, keep api clean/constant and expect user code to not break.
Thks, Amol On Tue, Nov 3, 2015 at 9:19 AM, Pramod Immaneni <pra...@datatorrent.com> wrote: > For 3 and 4 can't we strike a balance between not having to expose the > operators underneath and at the same time not having to write boilerplate > code for all the properties that the module wants to make available > outside. It can quickly become unmanageable. For example, an input operator > has a new connection property which can be used outside and now all the > modules using that operator, their code has to be modified to just add a > pass through setter/getter. How about treating the operator name as a group > name and ability for module developers to easily make available/specify all > or a subset of the properties of an operator to the user without having to > explicitly make each of them a module property. > > On Mon, Nov 2, 2015 at 5:00 PM, Amol Kekre <a...@datatorrent.com> wrote: > > > 3,4 should follow conventions where the creator decides the api > (including > > accessibility). In general only those properties exposed by module > creator > > should be settable. What the module internally does with them is module > > designer's call. Accessing internals of module from outside is uncommon. > > For exampe in Java (or C++) private fields/members are not to be > accessed. > > Properties (setter and getter) are the api that module designer gives to > > the module user. It is dangerous and has unintended consequences if > module > > user starts to access internals outside the api. > > > > Partitioning should be next phase. As long as current design does not > halt > > partitioning it should be ok (which I believe is true). > > > > Thks, > > Amol > > > > > > On Mon, Nov 2, 2015 at 3:44 PM, Vlad Rozov <v.ro...@datatorrent.com> > > wrote: > > > > > 1. +1, though passing original DAG to module's populateDAG() it is not > by > > > design and is the current pull request implementation details. > > > > > > 2. While I agree that both Module and StreamingApplication let's > > > module/application designer to expose DAG design reuse pattern and > > > StreamingApplication interface may be extending Module, it does not > seem > > to > > > buy us much. Do we want to allow certain applications to be reused as > > > Modules in other applications or should application package be > different > > > from Module package? The current approach is to distribute Modules as > > part > > > of .jar for example as part of Malhar library without necessarily > > providing > > > all necessary dependencies. Application package on other side must > > include > > > all dependencies not provided by the platform. > > > > > > 3, 4. While this will help Module designer, it may complicate Module > > > maintenance and how Modules are used. What if Module designer wants to > > > change it's implementation and replace one operator implementation with > > > another operator? Does StreamingApplication designer need to know > > internal > > > structure of Modules? Should Module be considered as a black box during > > > Application design time as it was initially planned? > > > > > > 5, 6, 7 +1. This is currently proposed behavior of Module functionality > > > the way I understand it. > > > > > > 8. We need to see what Module designer can specify for partitioning. > One > > > of supported cases should be ability to specify cascading partitioning > > > scheme. > > > > > > Thank you, > > > > > > Vlad > > > > > > > > > On 11/2/15 10:30, Pramod Immaneni wrote: > > > > > >> I have some comments and suggestions on the module design. I think > these > > >> need to be taken into account before we can merge the implementation > > >> provided below into the mainline code. I apologize if these should > have > > >> been brought up earlier as for some reason or the other I was out of > > loop > > >> on this one > > >> > > >> https://github.com/apache/incubator-apex-core/pull/148 > > >> < > > >> > > > https://github.com/apache/incubator-apex-core/pull/148#issuecomment-153104963 > > >> > > > >> > > >> 1. DAG scoping currently in the implementation is global for > > modules, > > >> each module's populateDAG sees the entire DAG. It should be locally > > scoped > > >> as one module does not and should not know about another. > > >> 2. The module has a populateDAG method with exact same syntax as > in > > >> StreamingApplication. Is StreamingApplication also a module, should it > > >> extend that interface. > > >> 3. Setting properties for modules is too verbose. Module > developer > > >> needs to repeat every property they want exposed with a setter and > > getter > > >> in JAVA. I don't disagree that module developer should be able to > choose > > >> which properties from which operators need to be exposed but the > current > > >> way seems to duplicate code. Here is a suggestion. > > >> a. Allow modules to specify which operators and properties > can > > >> be > > >> accessible from outside. One way is in the "populateDAG" method of the > > >> module when adding the operator have the ability to specify if this > > >> operator can be accessible from outside and which or all properties > can > > be > > >> accessible. > > >> b. Provide methods in ModuleMeta or elsewhere to set > property > > >> values by specifying the operator name (friendly name) inside the > module > > >> and property name. If this is allowed by a. above it is successful > else > > it > > >> should fail. > > >> c. Allow a syntax in property files to specify the property > in > > >> b. > > >> Example syntax dt.module.<modulename>.operator.<operatorname>.prop.< > > >> propname> > > >> 4. For attributes same mechanism as in 3 should apply for the > > >> operators > > >> that are exposed by the module. For property file, example syntax > > >> dt.module.<modulename>.operator.<operatorname>.attr.<attrname> > > >> 5. Module developers in addition to 3. and 4. above may choose to > > >> support module level properties and attributes. These should not be > the > > >> default when 3. and 4. are possible but complementary, in addition to > > >> them. > > >> In this case for properties they can implement setters and getters in > > the > > >> module. For attributes the user should still be able to set the > > attributes > > >> using the dag setAttribute method. You could introduce a method in the > > >> module to process attributes that can get called by the engine once > > >> everything is set. > > >> 6. For 5. above setting global properties and attributes for > module > > >> is > > >> akin to ideas that have been proposed for the application as well. A > > >> consistent way must be possible for applications as well even if it is > > not > > >> implemented now. > > >> 7. For 5. or 6. above there should be a property file way of > > >> specifying > > >> the global module properties and attributes. Example syntax > > >> dt.module.<modulename>.prop.<propname>, > > >> dt.module.<modulename>.attr.<attrname>. > > >> Notice the difference with 3. c. and 4 above that there is no operator > > >> keyword here. > > >> 8. Partitioning needs to be consistent with what the user will > > expect > > >> when they see module as an entity. I will send an image of possible > > >> examples of how the user will expect the physical plan to look in > > certain > > >> cases. > > >> > > >> Thanks > > >> > > >> > > > > > >
