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.

Transcript

1. Kotlin C Interop
   Matt Moore
   github: mattmoore twitter: mattmoore_io
   kotlinlang slack: mattmoore
   medium: mattmoore_io
   Rally Health
   https://www.builtinchicago.org/company/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
   cinterop
   Step 1:
   
   Create def file
   
   for library you
   
   want to use
   Step 2:
   
   Run cinterop
   
   to generate
   
   Kotlin library
   
   "libgreeter.klib"
   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
    libgreeter.klib
    libgreeter.dylib
    java -jar -Djava.library.path=/usr/local/lib build/Greeter.jar
    libgreeter_jni.dylib
    libgreeter.dylib
    Kotlin Native ~ vs ~ Kotlin JVM
    libgreeter_jni.h
    libgreeter_jni.c
    libgreeter.def
    

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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-
    native-code-835e93af7ddf
    Matt Moore
    Resources
    github: mattmoore twitter: mattmoore_io
    kotlinlang slack: mattmoore
    medium: mattmoore_io
    

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