You can also issue multiple calls in one "invoke()" call (have multiple Futures) and then chain these futures and return only something once all Futures are complete.
On Mon, Feb 20, 2017 at 4:01 PM, Till Rohrmann <trohrm...@apache.org> wrote: > In order to output 0 elements you have to pass an empty collection to the > `collect` method. > > You're right that our online documentation is lacking the fact that you're > only supposed to call `collect` once. It's actually documented in the > JavaDocs of this method. We should change this. > > You're also right that the name `AsyncCollector` is definitely not the best > name for reflecting what it actually represents. I think the initial idea > was to make it look similar to the existing functions which are given a > `Collector`. Actually it is a promise/completable future and as such we > should maybe name it "ResultPromise"/"ResultFuture". I've opened a JIRA > for > this [1]. > > [1] https://issues.apache.org/jira/browse/FLINK-5851 > > Cheers, > Till > > On Mon, Feb 20, 2017 at 3:41 PM, Gyula Fóra <gyula.f...@gmail.com> wrote: > > > Hi Till, > > > > Thanks, for the explanation! > > > > How do I express if I don't want to collect any elements in the async > > collector? Like 0 output from a flatmap. > > > > Also it doesn't seem to be specified anywhere that the AsyncCollector is > > "completed", it is just a collector. You should be able to collect > multiple > > things to it, but it actually won't work if you try to do that from more > > than one Future. > > > > I wonder if it would make sense to change the API to make this more > > specific otherwise we might keep a lot of unnecessary state or have > > potential leaks depending on the usage. > > > > Just my thoughts, now I also understand the current rationale just I > didn't > > completely get it for the first pass. > > > > Gyula > > > > Till Rohrmann <trohrm...@apache.org> ezt írta (időpont: 2017. febr. 20., > > H, > > 15:35): > > > > > Hi Gyula, > > > > > > the assumption is that the AsyncCollector is either completed by the > user > > > or, if you have a timeout defined, that it will be completed with a > > timeout > > > exception. This means that if you have no timeout defined, then you > have > > to > > > make sure that the collector is completed. Otherwise you will have > > > lingering state which is never cleared. In that sense it follows the > > > semantics of normal futures. > > > > > > What do you mean by creating more than one future? More than one future > > > which completes the AsyncCollector? If that's the case, then the first > > > future which completes will also complete the AsyncCollector and the > > result > > > of the other future should be ignored. > > > > > > Cheers, > > > Till > > > > > > > > > On Mon, Feb 20, 2017 at 2:53 PM, Gyula Fóra <gyf...@apache.org> wrote: > > > > > > > Hi, > > > > > > > > I was looking at the AsyncFunction interface and try to wrap my head > > > around > > > > the implementation and the assumptions and I have some questions, > maybe > > > > somebody could help me out :) > > > > > > > > What happens if the user does not collect any data or set a future to > > do > > > so > > > > in the invoke method? > > > > Also what happens if I create more than one Future? > > > > > > > > It seems that the "streamRecordBufferEntry" logic assumes that there > > > will > > > > be a Future that eventually collects 1 thing or the user does this > > > > directly. > > > > Do I understand correctly? If not I am probably missing the part > where > > > the > > > > buffer entry is removed immediately if no async request was made. > > > > > > > > Thank you! > > > > Gyula > > > > > > > > > >
