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![Copyright © 2017, Oracle and/or its affiliates. All rights reserved. 25
$ java -XX:AOTLibrary=./libHelloAOT.so HelloAOT
Hello AOT!
$ java -XX:+PrintAOT ¥
-XX:AOTLibrary=./libHelloAoT.so HelloAoT
13 1 loaded ./libHelloAoT.so aot library
76 1 aot[ 1] HelloAoT.<init>()V
76 2 aot[ 1] HelloAoT.main([Ljava/lang/String;)V
Hello AOT!
Run AOT compiled code](https://image.slidesharecdn.com/anothercompilationmethodinjava-aotaheadoftimecompilation-171118063750/85/Another-compilation-method-in-java-AOT-Ahead-of-Time-compilation-25-320.jpg)
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Another compilation method in java - AOT (Ahead of Time) compilation
The document discusses ahead-of-time (AOT) compilation in Java, which generates native machine code from Java bytecode ahead of runtime. AOT compilation was introduced in Java 9 as experimental and allows precompiling Java classes into shared library files that can be loaded by multiple JVMs. Benefits of AOT include faster startup times and improved performance by avoiding interpretation and just-in-time compilation overhead, though it currently has limitations such as only supporting Linux x64 and requiring the same system configuration.
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Another compilation method in java - AOT (Ahead of Time) compilation
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- 6. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. 6 For improvement of warm up time Tiered compilation C1 (-client/client use) C2 (-server/server use) •Longer compilation time and longer startup time, but generated code runs faster. • Heavy optimization • In case of prioritizing performance after invocation... • Shorter compilation time and shorter startup time, but generated code runs slow. • Less optimization • In case of prioritizing startup time...
- 7. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. 7 Compilation Level • 4: C2•0: Interpreter C2Interpreter C1 • 1: C1 full optimization (no profiling) • 2: C1 with profiling about invocation and back-edge only • 3: C1 full profiling (level2 + MDO) 1,500 10,000
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- 13. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. CDS/AppCDS (Class Data Sharing) • CDS is the scheme for sharing Java SE class library only. •In case of AppCDS, application classes are also included. 13 Class Data classes.jsa HotSpot HotSpot HotSpot HotSpot
- 14. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. Works for... • Quicker warmup • Lower total memory footprint Does not work for... •No feature to persist or share machine (native) code. 14 CDS/AppCDS
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- 16. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. 16 $ gcc-o HelloAoT HelloAoT.c In case of C...
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- 18. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. AOT Java Compilers • IBM Java SDK for AIX • IBM Java SDK for z/OS •Oracle Java ME Embedded Client • WebSphere Real Time • Gluon VM etc. 18
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- 20. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. AOT Supports Tiered Compilation • Non-tiered compilation mode (default) –Similar to C1 in Client VM –No collecting profiling information –No JIT recompilation if AOT code is not deoptimized. •Tied compilation mode (--compile-for-tiered) –Profiling level is as same as C1 Level 2. –If hitting AOT invocation thresholds, methods are recompiled by C1 at Level 3 first for gathering full profiling information. 20
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- 22. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. Benefits might be gained from AOT... • No compilation overhead at runtime. •Improve startup time and able to achieve peak performance faster. • Able to run on the platform where native code cannot be not generated at runtime (e.g. iOS, embedded). • Density improvement - Able to share native code. 22
- 23. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. 23 $ jaotc--output libHelloAOT.so HelloAOT.class $ jaotc --output libjava.base.so --module java.base $ jaotc --output libmyapp.so --jar myapp.jar $ jaotc -J-XX:+UseCompressedOops --output libHelloAOT.so HelloAOT.class How to use jaotc
- 24. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. jaotc does not resolve all referenced classes • jaotcdoes not resolve referenced classes which are not system classes or part of compiled classes. 1. Have to add referenced classes to class path. 2. Specify additional java modules 24 jaotc --output=libfoo.so --jar foo.jar ¥ -J-cp -J./ jaotc --output=libactivation.so --module ¥ java.activation -J--add-module=java.se.ee
- 25. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. 25 $ java-XX:AOTLibrary=./libHelloAOT.so HelloAOT Hello AOT! $ java -XX:+PrintAOT ¥ -XX:AOTLibrary=./libHelloAoT.so HelloAoT 13 1 loaded ./libHelloAoT.so aot library 76 1 aot[ 1] HelloAoT.<init>()V 76 2 aot[ 1] HelloAoT.main([Ljava/lang/String;)V Hello AOT! Run AOT compiled code
- 26. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. On JVM startup... • AOT initialization code looks for well-known AOT libraries in well- known location ($JAVA_HOME/lib) or libraries specified using -XX:AOTLibrary. • JVM knows AOT library name for the following Java modules. –java.base –jdk.compiler(javac) –jdk.scripting.nashorn (Nashorn) –jdk.internal.vm.ci (JVMCI) –jdk.internal.vm.compiler (Graal) 26
- 27. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. VM Options should be synchronized. • libjava.base.so -XX:-UseCompressedOops -XX:+UseG1GC •libjava.base-coop.so -XX:+UseCompressedOops -XX:+UseG1GC • libjava.base-nong1.so -XX:-UseCompressedOops -XX:+UseParallelGC • libjava.base-coop-nong1.so -XX:+UseCompressedOops -XX:+UseParallelGC 27
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- 29. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. Limitations • Experimental release • No support •No official document (except for JEP) 29 First of all...
- 30. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. Limitations • Available only when using either Parallel or G1 GC on Linux x64 with libelf.so. •AOT compilation must be executed on the same system or a system with the same configuration on which AOT code will be used by Java application. • Unable to compile java code using dynamically generated classes and bytecode (lambda expressions, InvokeDynamic) 30 These limitations are in Java 9, and may be addressed in future releases.
- 31. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. When and where to use AOT? • Event-driven services such as Functions • Embedded, IoT, mobile •Not often invoked classes... (not hot code) • Application code which should be protected from decompilers ...etc. 31 If AOT is officially supported and is available on several platforms...
- 32. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. Summary • Since Java 9 (HotSpot), AOT compilation is available, but positioned as experimental release and no official support. • AOT have several characteristics and is expected to improve performance of applications, especially such short-lived objects as functions •Working to remove current limitation and improve AOT. 32
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