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Kotlin C Interop

Kotlin C Interop

Kotlin is a great language! But what if you want to call an existing native library in Kotlin, or build your own native library for performance optimizations? This is also useful for making Kotlin a viable option for systems programming. Perhaps there’s an existing C or C++ library that would be great to have available in Kotlin, but it isn’t yet Kotlin-ready? We’ll take a look at how to access native libraries with Kotlin.

Matt Moore

August 23, 2019

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  1. Kotlin C Interop
    Matt Moore
    github: mattmoore twitter: mattmoore_io
    kotlinlang slack: mattmoore
    medium: mattmoore_io
    Rally Health

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  2. C Interop on Two Platforms
    • Kotlin Native

    • Kotlin JVM

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  3. Let's Build A C Library
    Step 1: greeter.h Step 2: greeter.c
    Step 3: Compile libgreeter.dylib

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  4. C-Interop for Kotlin Native
    • When you want to use the Kotlin language without the JVM

    • Easier working with other native modules (system libraries in C/C++)

    • System programming - C/C++/Golang can be painful!

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  5. C-Interop for Kotlin Native
    Step 1:

    Create def file

    for library you

    want to use
    Step 2:

    Run cinterop

    to generate

    Kotlin library

    Step 3:

    Import "libgreeter.klib"

    into Kotlin program

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  6. Create C-Interop Kotlin Native Library
    Step 2: Compile Kotlin library "libgreeter.klib"
    Step 1: libgreeter.def

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  7. Using libgreeter.klib
    Step 2: Compile
    Step 1: Main.kt

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  8. Kotlin JVM: JNI (Java Native Interface)
    • Need another C library libgreeter_jni.dylib to translate between the JVM
    and libgreeter.dylib

    • Load libgreeter_jni.dylib in Kotlin JVM project

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  9. Kotlin JVM: JNI Conversion Library
    Step 1: greeter_jni.h

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  10. Kotlin JVM: JNI Conversion Library
    Step 2: greeter_jni.c

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  11. Kotlin JVM: JNI Conversion Library
    Step 3: Compile C code in "hello_jni.c" to shared library "libhello_jni.dylib"

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  12. Kotlin JVM: Using JNI Conversion Library
    Step 5: Call "hello()" native function

    in Main.kt
    Step 4: Create Kotlin C-Interop class "Greeter.kt"
    Step 6: Compile + Run Greeter.jar

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  13. program.kexe
    java -jar -Djava.library.path=/usr/local/lib build/Greeter.jar
    Kotlin Native ~ vs ~ Kotlin JVM

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  14. Kotlin Native
    Kotlin JVM

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  15. How to Find Me
    Code/docs for this talk: https://github.com/mattmoore/kotlin-cinterop-talk

    Kotlin C-Interop: https://kotlinlang.org/docs/reference/native/c_interop.html

    Kotlin Native Overview: https://kotlinlang.org/docs/reference/native-overview.html

    Java Native Interface (JNI): https://medium.com/@mattmoore_io/kotlin-jni-for-
    Matt Moore
    github: mattmoore twitter: mattmoore_io
    kotlinlang slack: mattmoore
    medium: mattmoore_io

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