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add notes about jvm inheritance and defaults for kotlin daemon
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kaeawc committed Sep 20, 2024
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38 changes: 34 additions & 4 deletions docs/topics/gradle/gradle-compilation-and-caches.md
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Expand Up @@ -163,12 +163,22 @@ Each of the following ways to set arguments overrides the ones that came before

#### Gradle daemon arguments inheritance

If nothing is specified, the Kotlin daemon inherits arguments from the Gradle daemon. For example, in the `gradle.properties` file:
The Kotlin daemon inherits a specific set of arguments from the Gradle daemon and then overwrites them with JVM args specified for the Kotlin daemon. For example, in the `gradle.properties` file:

```none
org.gradle.jvmargs=-Xmx1500m -Xms500m
org.gradle.jvmargs=-Xmx1500m -Xms500m -XX:MaxMetaspaceSize=1g
```

would then result in the Kotlin daemon's JVM args being:

```none
-Xmx1500m -XX:ReservedCodeCacheSize=320m -XX:MaxMetaspaceSize=1g -XX:UseParallelGC -ea -XX:+UseCodeCacheFlushing -XX:+HeapDumpOnOutOfMemoryError -Djava.awt.headless=true -Djava.rmi.server.hostname=127.0.0.1 --add-exports=java.base/sun.nio.ch=ALL-UNNAMED
```

> Learn more about [Kotlin daemon's behavior with JVM arguments](#kotlin-daemon-s-behavior-with-jvm-arguments).
>
{type="note"}

#### kotlin.daemon.jvm.options system property

If the Gradle daemon's JVM arguments have the `kotlin.daemon.jvm.options` system property – use it in the `gradle.properties` file:
Expand All @@ -193,12 +203,16 @@ When passing arguments, follow these rules:

#### kotlin.daemon.jvmargs property

You can add the `kotlin.daemon.jvmargs` property in the `gradle.properties` file:
You can add the `kotlin.daemon.jvmargs` property in the `gradle.properties` file. Note that if you do not specify `ReservedCodeCacheSize` here or in Gradle's JVM args, a default will be applied by the Kotlin Gradle plugin:

```none
kotlin.daemon.jvmargs=-Xmx1500m -Xms500m
```

```none
-Xmx1500m -XX:ReservedCodeCacheSize=320m -Xms500m
```

#### kotlin extension

You can specify arguments in the `kotlin` extension:
Expand Down Expand Up @@ -265,7 +279,23 @@ When configuring the Kotlin daemon's JVM arguments, note that:
> even if other requested JVM arguments are different, this daemon will be reused instead of starting a new one.
>
{type="note"}
* If the `Xmx` argument is not specified, the Kotlin daemon will inherit it from the Gradle daemon.

If the following arguments are not specified, the Kotlin daemon will inherit them from the Gradle daemon:

* -Xmx
* -XX:MaxMetaspaceSize
* -XX:ReservedCodeCacheSize (Defaults to 320m if not inherited and unspecified)

The Kotlin daemon also has a number of defaults:
* -XX:UseParallelGC (if no other garbage collector was set)
* -ea
* -XX:+UseCodeCacheFlushing
* -XX:+HeapDumpOnOutOfMemoryError
* -Djava.awt.headless=true
* -D{java.servername.property}={localhostip}
* --add-exports=java.base/sun.nio.ch=ALL-UNNAMED (Only for JDK 16+)

You can use a tool like [VisualVM](https://visualvm.github.io/) to verify what the actual settings of a running JVM process like the Kotlin daemon are.

## Rolling back to the previous compiler

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