改进 Kotlin/Native 编译时间的技巧

The Kotlin/Native compiler is constantly receiving updates that improve its performance. With the latest Kotlin/Native compiler and a properly configured build environment, you can significantly improve the compilation times of your projects with Kotlin/Native targets.

Read on for our tips on how to speed up the Kotlin/Native compilation process.

General recommendations

  • Use the most recent version of Kotlin. This way you will always have the latest performance improvements.
  • Avoid creating huge classes. They take a long time to compile and load during execution.

  • Preserve downloaded and cached components between builds. When compiling projects, Kotlin/Native downloads the required components and caches some results of its work to the $USER_HOME/.konan directory. The compiler uses this directory for subsequent compilations, making them take less time to complete.

    When building in containers (such as Docker) or with continuous integration systems, the compiler may have to create the ~/.konan directory from scratch for each build. To avoid this step, configure your environment to preserve ~/.konan between builds. For example, redefine its location using the kotlin.data.dir Gradle property.

    Alternatively, you can use the -Xkonan-data-dir compiler option to configure your custom path to the directory via the cinterop and konanc tools.

Gradle configuration

The first compilation with Gradle usually takes more time than subsequent ones due to the need to download the dependencies, build caches, and perform additional steps. You should build your project at least twice to get an accurate reading of the actual compilation times.

Here are some recommendations for configuring Gradle for better compilation performance:

  • Increase the Gradle heap size. Add org.gradle.jvmargs=-Xmx3g to gradle.properties. If you use parallel builds, you might need to choose the right number of workers with the org.gradle.workers.max property or the --max-workers command-line option. The default value is the number of CPU processors.

  • Build only the binaries you need. Don't run Gradle tasks that build the whole project, such as build or assemble, unless you really need to. These tasks build the same code more than once, increasing the compilation times. In typical cases such as running tests from IntelliJ IDEA or starting the app from Xcode, the Kotlin tooling avoids executing unnecessary tasks.

    If you have a non-typical case or build configuration, you might need to choose the task yourself.

    • linkDebug*: To run your code during development, you usually need only one binary, so running the corresponding linkDebug* task should be enough. Keep in mind that compiling a release binary (linkRelease*) takes more time than compiling a debug one.

    • packForXcode: Since iOS simulators and devices have different processor architectures, it's a common approach to distribute a Kotlin/Native binary as a universal (fat) framework. During local development, it will be faster to build the .framework for only the platform you're using.

      To build a platform-specific framework, call the packForXcode task generated by the Kotlin Multiplatform project wizard.

      Remember that in this case, you will need to clean the build using ./gradlew clean after switching between the device and the simulator. See this issue for details.

  • Don't disable the Gradle daemon without having a good reason to. Kotlin/Native runs from the Gradle daemon by default. When it's enabled, the same JVM process is used and there is no need to warm it up for each compilation.

  • Don't use transitiveExport = true. Using transitive export disables dead code elimination in many cases: the compiler has to process a lot of unused code. It increases the compilation time. Use export explicitly for exporting the required projects and dependencies.

  • Use the Gradle build caches:

    • Local build cache: Add org.gradle.caching=true to your gradle.properties or run with --build-cache on the command line.
    • Remote build cache in continuous integration environments. Learn how to configure the remote build cache.

  • Enable previously disabled features of Kotlin/Native. There are properties that disable the Gradle daemon and compiler caches – kotlin.native.disableCompilerDaemon=true and kotlin.native.cacheKind=none. If you had issues with these features before and added these lines to your gradle.properties or Gradle arguments, remove them and check whether the build completes successfully. It is possible that these properties were added previously to work around issues that have already been fixed.

  • Try incremental compilation of klib artifacts. With incremental compilation, if only a part of the klib artifact produced by the project module changes, just a part of klib is further recompiled into a binary.

    This feature is Experimental. To enable it, add the kotlin.incremental.native=true option to your gradle.properties file. If you face any problems, create an issue in YouTrack.

Windows OS configuration

  • Configure Windows Security. Windows Security may slow down the Kotlin/Native compiler. You can avoid this by adding the .konan directory, which is located in %\USERPROFILE% by default, to Windows Security exclusions. Learn how to add exclusions to Windows Security.