The document discusses GraalVM, a high-performance, polyglot virtual machine that offers native image support for various programming languages including Java, Scala, Kotlin, and others. It highlights features such as instant startup, low footprint, and the ability to compile applications ahead-of-time into machine code, enhancing memory management and security. Furthermore, it provides guidance on static initializers and includes configuration options relevant for building native images.

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Oleg Šelajev
GraalVM team, Oracle Labs
@shelajev
Native Images

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Safe Harbor Statement
The following is intended to provide some insight into a line of research in Oracle
Labs. It is intended for information purposes only, and may not be incorporated
into any contract. It is not a commitment to deliver any material, code, or
functionality, and should not be relied upon in making purchasing decisions. The
development, release, and timing of any features or functionality described in
connection with any Oracle product or service remains at the sole discretion of
Oracle. Any views expressed in this presentation are my own and do not
necessarily reflect the views of Oracle.
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Seeing is believing

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Fast Java, Scala, Kotlin, Groovy, Clojure...
Instant startup, low footprint
Polyglot & embeddable
Interoperability between languages: node.js, Python, Ruby, R
Why GraalVM?

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Fast Java, Scala, Kotlin, Groovy, Clojure...
Instant startup, low footprint
Polyglot & embeddable
Interoperability between languages: node.js, Python, Ruby, R
Why GraalVM?

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GraalVM native images

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Native images
• Full AOT compilation to machine code
• Works with memory management
• Secure execution (e.g., bounds checks)
• Embeddable with native applications

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Native images
• Full AOT compilation to machine code
• Works with memory management
• Secure execution (e.g., bounds checks)
• Embeddable with native applications

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Image build time Runtime
Native image lifecycle

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Static initializers
Static class initialization blocks, pre-initialized static variables.

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Static initializers
By default static class initialization is done
during native image construction.
Large static data structures are pre-allocated
allowing faster startup of the generated image.
No instance-specific initializations can be done in static
initializers.

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Static initializers - things not to do
• start application threads that continue to run in the background
• load native libraries using `java.lang.Runtime.load(String)`
• open files or sockets, or
• allocate C memory, e.g., `java.nio.ByteBuffer.allocateDirect(int)`.

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Static initializers
Write your own initialization methods
and call them explicitly from your main entry point.

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> $JAVA_HOME/bin/javac HelloStartupTime.java
> $JAVA_HOME/bin/java HelloStartupTime
Startup: Fri Aug 31 13:17:05 PDT 2018
Now: Fri Aug 31 13:17:05 PDT 2018

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> $JAVA_HOME/bin/javac HelloStartupTime.java
> $JAVA_HOME/bin/java HelloStartupTime
Startup: Fri Aug 31 13:17:05 PDT 2018
Now: Fri Aug 31 13:17:05 PDT 2018

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> $JAVA_HOME/bin/javac HelloStartupTime.java
> $JAVA_HOME/bin/java HelloStartupTime
Startup: Fri Aug 31 13:17:05 PDT 2018
Now: Fri Aug 31 13:17:05 PDT 2018
> $JAVA_HOME/bin/native-image HelloStartupTime
> ./hellostartuptime
Startup: Fri Aug 31 13:22:12 PDT 2018
Now: Fri Aug 31 14:35:42 PDT 2018

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Static initializers config
--initalize-at-build-time=package
--initialize-at-run-time=p.C1
-H:+PrintClassInitialization

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Reflection
-H:ReflectionConfigurationFiles=

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Resources
-H:IncludeResources=<regexp>
-H:IncludeResources=
"application.yml|META-INF/services/*.*"

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-H:+ReportUnsupportedElementsAtRuntime
--allow-incomplete-classpath
!27
java.lang.NoClassDefFoundError

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Substitutions
Core classes (annotations):
com.oracle.svm.core.annotate.TargetClass
com.oracle.svm.core.annotate.Substitute

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Image build time vs runtime

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native-image.properties
META-INF/native-image/

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native-image.properties
META-INF/native-image/groupId/artifactId/
reflection-config.json
META-INF/native-image/groupId/artifactId/
native-image.properties

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native-image.properties
ImageName = netty-server
Args = --features=com.oracle.svm.nettyplot.PlotterSingletonFeature
-H:ReflectionConfigurationResources=${.}/reflection-config.json
--delay-class-initialization-to-runtime=
io.netty.handler.codec.http.HttpObjectEncoder
-H:+SpawnIsolates

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https://medium.com/graalvm/instant-netty-startup-using-graalvm-native-
image-generation-ed6f14ff7692

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https://github.com/spring-projects/spring-framework/wiki/GraalVM-native-image-support

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Work in progress

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GC

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Heapdump
-H:+AllowVMInspection
$ ps -e | grep native-name
$ kill -SIGUSR1 <pid>

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Runtime
https://github.com/giltene/wrk2

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Runtime
https://github.com/giltene/wrk2

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https://github.com/PPACI/wrk2img

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High performance, polyglot, language-level virtualization layer…
embeddable across the stack
in native and JVM-based applications.

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