Swift/Java Interop Community Call #1

Development Java interoperability
4

Meeting notes from the first Swift/Java interoperability call.

Swift Java Community Call Notes

  • Konrad
  • Mads
  • Thomas
  • Greg
  • Joannis
  • Marc
  • Finagolfin*

Agenda:

  • Swift Java “JNI only” Package status -- Marc

    • Konrad: Working through it, following swiftlang repo creation process, should hopefully have it done soon

  • Android & JNIOnLoad fun? -- Mads

    • 28 ang below we could load libart etc.
    • above 30? there's official api access
    • Mads: would be good to not have different strategies for every platform
    • Preferred: OnLoad and store the vm ref
      • calling the createJVM probably we don't care about
    • We wait on swift-java-jni probably
    • concerned about linking
      • We currently static link swift-java lib;
    • Official way is the JNIOnLoad on load time of the lib
      • Marc: only problem is that its not transitively called
      • The "get jvms" API does not work on 29, and 30; so we can't use that
      • Standard way in SKIP: manually call during app startup, call into a native function and hang onto jvm from there
    • ACTION: Wait till we do swift-java-jni, then cooperate on something that should serve most if not all use-cases nicel

  • How can we contribute, is there some guide about patterns to follow? -- Greg

    • Focus on interop API; say we wanted to contribute nonescaping closures etc.
    • Architecturally explain maybe explain some more.
    • ACTION: Konrad to write up some architectural hints to help "how to contribite", mark some issues as “good first issue”

  • (Old) Android example issues -- Thomas

    • Sounds like this was about Mads’ old example; the new example should be easier to follow, but please file issues or PR if something’s off about it still.
    • Had some issues with the android swift-java example
    • Android SDK 6.2 release mixup in SDKs perhaps caused issues?
    • Mads: This sounds like the old example, that is expected
    • Try the new example: hello-swift-java

  • Packaging and how to link – Mads

    • Mads: how do we package things, i.e. do we static link "single big project with all dependencies"
      • We need a way to express where our dependencies are for jextract for this
    • Marc: everything in SKIP is forced to be dynamic linked; The static linking in theory is interesting
      • However in practice the static linking if two libs do that that's bad.
      • Currently SKIP mandate all dependencies
      • Currently: SwiftPM has no way to force "all static"
      • Should we do a feature to "force dynamic libs in this build"
        • Not all dependencies CAN be static linked so this is a safer bet; more general
    • There's problems about version clashes like if multiple dependencies do depend on sqlite etc.
      • e.g. GRDB has top level packages because GRDB-dynamic
    • ACTION: Konrad, make an issue about the linking discussion

  • ACTION: Greg, some quick update to the android example how to add dependencies

Status updates:

  • Mads:
    • jextract+jni: async funcs are now imported as CompletableFutures (API 24)
    • jextract+jni: working on nested types in Swift
    • jextract+jni: implementing Java "interfaces" as protocols using Swift type
  • Konrad:
    • Working on calling Java funcs from Swift and automatic import of Java APIs (wrap-java)
  • Please try things out and report issues for things that don’t work

Gradle plugins / building:

  • Konrad: Discussion about building -linux-arm64-6.2.1.jar etc, vs REALLY fat jars etc
    • Really use-case dependent, some people want one or the other; a Gradle plugin could simplify this a bit, because it’s really tricky to get right at first.
  • Marc: Skip builds
    • AAR, every swift build takes the .so files and bindings and THEN the AARs are put together into an APK
  • ABI compatibility discussion
    • Lack of ABI kinda troublesome adoption because matching Swift versions would lead to “everyone rebuild for new Swift version”, however short term this may be managable;
    • This is kind of new with the arrival of swift-java and jars which contain binary compiled Swift; Server projects didn’t really encounter this up until now.

Next call

We will schedule another call in 2 weeks time, I will share a meeting link and exact date in a new forums thread.

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Swift/Java Interop Community Call: November 27th