Taming the Kotlin Compiler (Droidcon TO 2019)

As more and more Android code is being written in Kotlin, and many developers are switching over from Java, the performance of the Kotlin compiler has become a hot discussion topic. Javac has been tuned and optimized for many years, so how does kotlinc compare?

In addition, there are a whole new family of tools around kotlinc, such as kapt, the Kotin Gradle plugin and more. How can one use them efficiently to get optimal performance?

In this talk, we’ll take a deep dive into the following:

* Is Kotlin slower than Java? Should you worry?
* Caching and incrementality of Kotlin compilation
* How to use Kotlin with Gradle efficiently
* What is compilation avoidance and what are the state of things in Kotlin?
* Kotlin compilation in the context of Android

This talk will help you develop a better understanding of how your code is built, what performance bottlenecks exist in the toolchain, and how to avoid them to improve your build times.

Co-Presented with @Egorand.

Video: coming soon!

Transcript

1. Taming the Kotlin Compiler
3. $ git log commit 59da358e7aef1109fb71d964f846e9dcb61517c6 Author: Matt Precious <…@squareup.com> Date: Fri Nov 10 10:47:32 2017 Activity contact header tweaks $ find . -name *.java | wc -l 1122 $ find . -name *.kt | wc -l 330
4. $ git log commit c9ba9967bfdb3cdde63a336ef91001040b57fed0 Author: Andrew Tran <…@squareup.com> Date: Fri Nov 8 15:04:30 2019 Updating selection blocker to respect help items $ find . -name *.java | wc -l 209 $ find . -name *.kt | wc -l 2611
8. for(i in 1..N) {a // write N java files }a
9. for(i in 1..N) {a val javaclassfile = File(javaSourcesDir, "JavaTemp$i.java") javaclassfile.use {bout -> out.println("class JavaTemp$i {}") }b }a
10. for(i in 1..N) {a val javaclassfile = File(javaSourcesDir, "JavaTemp$i.java") javaclassfile.use {bout -> out.println("class JavaTemp$i {}") }b val process = ProcessBuilder() .command("time", "javac", "…") .start() val timeOutput = process.errorStream.use(BufferedReader::readLine) val tokens = timeOutput.split("\\s+".toRegex()) outputLogger.use {blog -> log.write("$i\t${tokens[1]}\t${tokens[3]}\t${tokens[5]}\n") }b }a
11. for(i in 1..N) {a appendWriter.use {csources -> val javaclassfile = File(javaSourcesDir, "JavaTemp$i.java") javaclassfile.use {bout -> out.println("class JavaTemp$i {}") }b sources.write("$javaclassfile\n") }c val process = ProcessBuilder() .command("time", "javac", "@javasources/sources") .start() val timeOutput = process.errorStream.use(BufferedReader::readLine) val tokens = timeOutput.split("\\s+".toRegex()) outputLogger.use {blog -> log.write("$i\t${tokens[1]}\t${tokens[3]}\t${tokens[5]}\n") }b }a
12. for(i in 1..N) {a appendWriter.use {csources -> val ktclassfile = File(ktSourcesDir, "KotlinTemp$i.kt") ktclassfile.use {bout -> out.println("class KotlinTemp$i {}") }b sources.write("$ktclassfile\n") }c val process = ProcessBuilder() .command("time", "kotlinc", "@ktsources/sources") .start() val timeOutput = process.errorStream.use(BufferedReader::readLine) val tokens = timeOutput.split("\\s+".toRegex()) outputLogger.use {blog -> log.write("$i\t${tokens[1]}\t${tokens[3]}\t${tokens[5]}\n") }b }a
15. for(i in 1..N) {a appendWriter.use {csources -> val javaclassfile = File(javaSourcesDir, "JavaTemp$i.java") javaclassfile.use {bout -> out.println("class JavaTemp$i {}") }b sources.write("$javaclassfile\n") }c val process = ProcessBuilder() .command("time", "javac", "@javasources/sources") .start() val timeOutput = process.errorStream.use(BufferedReader::readLine) val tokens = timeOutput.split("\\s+".toRegex()) outputLogger.use {blog -> log.write("$i\t${tokens[1]}\t${tokens[3]}\t${tokens[5]}\n") }b }a
16. for (( i=1; i<="$N"; i++ )) do JAVACLASSFILE="$SOURCES/JavaTemp$i.java" echo "package app.cash.droidcon.to;" >> "$JAVACLASSFILE" echo "class JavaTemp$i {}" >> "$JAVACLASSFILE" TIMED=$(time (./gradlew java:assemble > /dev/null) 2>&1) DATA=$(echo -n "$TIMED" | cut -f2 -d'm' | cut -f1 -d's' | tr '\n' '\t') echo "$i$DATA" >> "$OUTPUT" done
22. https://bit.ly/32DOCyf
25. CardCustomizationData
26. TouchData CardCustomizationData CardTheme
27. TouchData Stroke StampCustomization CardCustomizationData CardTheme
28. TouchData Stroke StampCustomization Point CardCustomizationData CardTheme
32. :presenters :backend:api :app :backend:jvm https://git.io/JervG
33. :presenters :backend:api :app :backend:jvm https://git.io/JervG kotlin-jvm com.android.library kotlin-android com.android.library kotlin-android kotlin-kapt com.android.application kotlin-android kotlin-kapt
34. kapt?
36. http://bit.ly/2CDcSWx
38. :presenters :backend:api :app :backend:jvm
40. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
41. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
42. class RealGreeter @Inject constructor() : Greeter { override fun greeting(name: String): Observable<Greeting> { return Observable .just(Greeting(message = "Hello $name!")) .delay(2, SECONDS) } } kaptGenerateStubsDebugKotlin
43. class RealGreeter @Inject constructor() : Greeter { override fun greeting(name: String): Observable<Greeting> { return Observable .just(Greeting(message = "Hello $name!")) .delay(2, SECONDS) } } @kotlin.Metadata(…) public final class RealGreeter implements Greeter { @NotNull @Override public Observable<Greeting> greeting(@NotNull String name) { return null; } @Inject public RealGreeter() { super(); } } kaptGenerateStubsDebugKotlin
44. class RealGreeter @Inject constructor() : Greeter { override fun greeting(name: String): Observable<Greeting> { return Observable .just(Greeting(message = "Hello $name!")) .delay(2, SECONDS) } } @kotlin.Metadata(…) public final class RealGreeter implements Greeter { @NotNull @Override public Observable<Greeting> greeting(@NotNull String name) { return null; } @Inject public RealGreeter() { super(); } } kaptGenerateStubsDebugKotlin ABI = Application Binary Interface
45. class RealGreeter @Inject constructor() : Greeter { val publicField: Foo override fun greeting(name: String): Observable<Greeting> { … } } Application Binary Interface
46. class RealGreeter @Inject constructor() : Greeter { val publicField: Foo override fun greeting(name: String): Observable<Greeting> { … } } Application Binary Interface
47. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
48. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
49. @kotlin.Metadata(…) public final class RealGreeter implements Greeter { @NotNull @Override public Observable<Greeting> greeting(@NotNull String name) { return null; } @Inject public RealGreeter() { super(); } } kaptDebugKotlin public final class GreeterPresenter { @Inject Greeter greeter; public void present() {…} }
50. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
51. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
52. kaptGenerateStubsDebugKotlin kaptDebugKotlin compileDebugKotlin
54. Why are my builds slow?
55. $ ./gradlew :app:assembleDebug BUILD SUCCESSFUL in 19s See the profiling report at: file:///Users/egor/.../cash/build/reports/ profile/profile-2019-11-11-11-33-51.html --profile
58. $ echo kotlin.build.report.enable=true >> ~/.gradle/gradle.properties $ ./gradlew :app:assembleDebug $ echo kotlin.build.report.verbose=true >> ~/.gradle/gradle.properties Kotlin build report is written to /Users/egor/…/DCTO19CashApp/build/ reports/kotlin-build/DCTO19CashApp-build-2019-11-11-11-37-23.txt BUILD SUCCESSFUL in 19s
61. Build cache Since Kotlin 1.2.21
63. $ ./gradlew clean $ ./gradlew app:assembleDebug
66. Incremental compilation Since Kotlin 1.1.1
67. Incremental kapt Since Kotlin 1.3.30 Incremental compilation Since Kotlin 1.1.1
68. $ ./gradlew :app:assembleDebug $ echo “class Test2” >> app/src/…/MainActivity.kt $ ./gradlew :app:assembleDebug
74. Non-incremental compilation
75. $ ./gradlew clean $ ./gradlew :app:assembleDebug $ echo “class Test3” >> app/src/…/MainActivity.kt $ ./gradlew :app:assembleDebug // FROM-CACHE
83. http://bit.ly/34ZN5UQ
84. https://github.com/JetBrains/kotlin/blob/master/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/ jetbrains/kotlin/gradle/tasks/Tasks.kt#L128
85. Compilation avoidance
86. If a dependency has changed in an ABI- compatible way (only its private API has changed), then Java compilation tasks will be up to-date. This means that if project A depends on project B and a class in B is changed in an ABI-compatible way (typically, changing only the body of a method), then Gradle won't recompile A.
87. :app :presenters implementation // Add “private val a = 1” to presenters/ …/GreeterPresenter.kt $ ./gradlew :app:assembleDebug
97. How do I debug my builds?
98. kotlin.build.report.enable=true kotlin.build.report.verbose=true … $ ./gradlew :app:assembleDebug Kotlin build report is written to /Users/egor/…/DCTO19CashApp/build/ reports/kotlin-build/DCTO19CashApp-build-2019-11-11-11-37-23.txt BUILD SUCCESSFUL in 19s ~/.gradle/gradle.properties
99. gradle.taskGraph.afterTask { task -> println " inputs: " task.inputs.files.each { println " " + it } println " outputs: " task.outputs.files.each { println " " + it } } ~/.gradle/gradle.properties
100. > Task :app:kaptGenerateStubsDebugKotlin inputs: … outputs: …/app/build/tmp/kapt3/incrementalData/debug …/app/build/tmp/kapt3/stubs/debug > Task :app:kaptDebugKotlin inputs: … outputs: …/app/build/tmp/kapt3/classes/debug …/app/build/generated/source/kapt/debug …/app/build/generated/source/kaptKotlin/debug > Task :app:compileDebugKotlin inputs: … outputs: …/app/build/tmp/kotlin-classes/debug
101. $ fswatch -xrt \ app/build/tmp/kapt3/incrementalData/debug \ app/build/tmp/kapt3/stubs/debug \ app/build/tmp/kapt3/classes/debug \ app/build/generated/source/kapt/debug \ app/build/generated/source/kaptKotlin/debug \ app/build/tmp/kotlin-classes/debug
102. $ fswatch -xrt \ app/build/tmp/kapt3/incrementalData/debug \ app/build/tmp/kapt3/stubs/debug \ app/build/tmp/kapt3/classes/debug \ app/build/generated/source/kapt/debug \ app/build/generated/source/kaptKotlin/debug \ app/build/tmp/kotlin-classes/debug $ ./gradlew app:aDebug
103. …/app/build/tmp/kotlin-classes/debug/…/cashapp/GreeterView.class Removed IsFile …/app/build/tmp/kotlin-classes/debug/…/cashapp Removed IsDir …/app/build/tmp/kotlin-classes/debug/…/cashapp Created IsDir …/app/build/tmp/kotlin-classes/debug/…/cashapp/GreeterView.class Created Updated IsFile
105. https://bit.ly/2CI8GF7
108. @jrodbx @egorand