Another compilation method in java - AOT (Ahead of Time) compilation

Copyright©2017,Oracleand/oritsaffiliates.Allrightsreserved.

AnothercompilationmethodinJavaAOT(AheadofTime)Compilation

AkihiroNishikawaOracleCorporationJapan

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SafeHarborStatementThefollowingisintendedtooutlineourgeneralproductdirection.Itisintendedforinformationpurposesonly,andmaynotbeincorporatedintoanycontract.Itisnotacommitmenttodeliveranymaterial,code,orfunctionality,andshouldnotberelieduponinmakingpurchasingdecisions.Thedevelopment,release,andtimingofanyfeaturesorfunctionalitydescribedforOracle’sproductsremainsatthesolediscretionofOracle.

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Agenda

JIT(Just-in-Time)Compilation

AOT(Ahead-of-Time)Compilation

Limitations

Summary

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Copyright©2017,Oracleand/oritsaffiliates.Allrightsreserved. 4

Inthissession,ImainlycoverHotSpot.


JIT(JustinTime)Compilation

SourceCode(*.java)

javac

Classfile(*.class)

HotSpot

Compile


ForimprovementofwarmuptimeTieredcompilation

C1(-client/clientuse) C2(-server/serveruse)

• Longercompilationtimeandlongerstartuptime,butgeneratedcoderunsfaster.

• Heavyoptimization

• Incaseofprioritizingperformanceafterinvocation...

• Shortercompilationtimeandshorterstartuptime,butgeneratedcoderunsslow.

• Lessoptimization

• Incaseofprioritizingstartuptime...


CompilationLevel

• 4:C2• 0:Interpreter

C2Interpreter C1

• 1:C1fulloptimization(noprofiling)• 2:C1withprofilingaboutinvocationandback-edgeonly• 3:C1fullprofiling(level2+MDO)

1,500 10,000


AOT– AheadOfTimecompilation•Generatenativecodeinadvance

• JEP295

•BasedonGraal

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AOTCompilation

SourceCode(*.java)

javac

Classfile(*.class)

HotSpot

jaotc

Sharedobjectfile(*.so)


*.java

javac

*.class HotSpot

jaotc

*.so

javac Compile


*.so

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Abletoshare“*.so”fileamongJVMs

HotSpot

HotSpot

HotSpot

HotSpot


AOTlookslikeCDS/AppCDS…

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CDS/AppCDS (ClassDataSharing)• CDSistheschemeforsharingJavaSEclasslibraryonly.• IncaseofAppCDS,applicationclassesarealsoincluded.

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ClassDataclasses.jsa

HotSpot

HotSpot

HotSpot

HotSpot


Worksfor...• Quickerwarmup• Lowertotalmemoryfootprint

Doesnotworkfor...• Nofeaturetopersistorsharemachine(native)code.

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CDS/AppCDS


IsAOTanewcompilationmethod?

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$ gcc -o HelloAoT HelloAoT.c

IncaseofC...


HowaboutotherJavaimplementations?

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AOTJavaCompilers• IBMJavaSDKforAIX

• IBMJavaSDKforz/OS

• OracleJavaMEEmbeddedClient

•WebSphereRealTime

• GluonVMetc.

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DoesAOTsupporttieredcompilation(C1/C2)?

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AOT SupportsTieredCompilation• Non-tieredcompilationmode(default)–SimilartoC1inClientVM–Nocollectingprofilinginformation–NoJITrecompilationifAOTcodeisnotdeoptimized.

• Tiedcompilationmode(--compile-for-tiered)–ProfilinglevelisassameasC1Level2.– IfhittingAOTinvocationthresholds,methodsarerecompiledbyC1atLevel3firstforgatheringfullprofilinginformation.

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WhatdoesAOTworkfor?

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Benefitsmight begainedfromAOT...• Nocompilationoverheadatruntime.• Improvestartuptimeandabletoachievepeakperformancefaster.• Abletorunontheplatformwherenativecodecannotbenotgeneratedatruntime(e.g.iOS,embedded).• Densityimprovement- Abletosharenativecode.

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$ 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

Howtousejaotc


jaotc doesnotresolveallreferencedclasses• jaotc doesnotresolvereferencedclasseswhicharenotsystemclassesorpartofcompiledclasses.1. Havetoaddreferencedclassestoclasspath.

2. Specifyadditionaljavamodules

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jaotc --output=libfoo.so --jar foo.jar ¥-J-cp -J./

jaotc --output=libactivation.so --module ¥java.activation -J--add-module=java.se.ee


$ java -XX:AOTLibrary=./libHelloAOT.so HelloAOTHello AOT!

$ java -XX:+PrintAOT ¥-XX:AOTLibrary=./libHelloAoT.so HelloAoT13 1 loaded ./libHelloAoT.so aot library76 1 aot[ 1] HelloAoT.<init>()V76 2 aot[ 1] HelloAoT.main([Ljava/lang/String;)V

Hello AOT!

RunAOTcompiledcode


OnJVMstartup...• AOTinitializationcodelooksforwell-knownAOTlibrariesinwell-knownlocation($JAVA_HOME/lib)orlibrariesspecifiedusing-XX:AOTLibrary.• JVMknowsAOTlibrarynameforthefollowingJavamodules.–java.base–jdk.compiler (javac)–jdk.scripting.nashorn (Nashorn)–jdk.internal.vm.ci (JVMCI)–jdk.internal.vm.compiler (Graal)

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VMOptionsshouldbesynchronized.• 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

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Limitations

• Experimentalrelease• Nosupport• Noofficialdocument(exceptforJEP)

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Firstofall...


Limitations

• AvailableonlywhenusingeitherParallelor G1GConLinuxx64withlibelf.so.• AOTcompilationmustbeexecutedonthesamesystem orasystemwiththesameconfiguration onwhichAOTcodewillbeusedbyJavaapplication.• Unabletocompilejavacodeusingdynamicallygeneratedclassesandbytecode (lambdaexpressions,InvokeDynamic)

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TheselimitationsareinJava9,andmaybeaddressedinfuturereleases.


WhenandwheretouseAOT?

• Event-drivenservicessuchasFunctions• Embedded,IoT,mobile• Notofteninvokedclasses...(nothotcode)• Applicationcodewhichshouldbeprotectedfromdecompilers

...etc.

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IfAOTisofficiallysupportedandisavailableonseveralplatforms...


Summary• SinceJava9(HotSpot),AOTcompilationisavailable,butpositionedasexperimentalreleaseandnoofficialsupport.

• AOThaveseveralcharacteristicsandisexpectedtoimproveperformanceofapplications,especiallysuchshort-livedobjectsasfunctions

•WorkingtoremovecurrentlimitationandimproveAOT.

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SafeHarborStatementTheprecedingisintendedtooutlineourgeneralproductdirection.Itisintendedforinformationpurposesonly,andmaynotbeincorporatedintoanycontract.Itisnotacommitmenttodeliveranymaterial,code,orfunctionality,andshouldnotberelieduponinmakingpurchasingdecisions.Thedevelopment,release,andtimingofanyfeaturesorfunctionalitydescribedforOracle’sproductsremainsatthesolediscretionofOracle.

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Another compilation method in java - AOT (Ahead of Time) compilation

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