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Jeannie: Granting Java Native Interface Developers their Wishes

Martin Hirzel Robert GrimmIBM Watson Research Center New York University

October 23, 2007

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FFI: Foreign Function Interface

UserProgram

—nqueens

Virtual Execution Environment —JVM

Operating System —Linux

StandardLibraries

— java.io

CustomLibraries

—JavaBDD

Motivation:• OS Services• Legacy Code• Performance• Convenience

Blue:C

Brown:Java

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QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

JNI = Java Native InterfaceJava

C

Native method:no body in Java

C function with mangled nameimplements Java method

Read Javafield from C

Throw Javaexception from C

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FFI Design Goals

Productivity– Writing & maintaining code

Safety– Preventing & detecting bugs

Efficiency– At transition & elsewhere

Portability– Different OS, HW, virtual execution environment

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QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Jeannie Example

Native methods have a body

Nestedblock

Can nest toany depth

Can useshort names

Nestedexpression

Support fullC syntax

Exception handling in C

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Jeannie Build ProcessSocket.jni

Socket.jni.i

Preprocessor

Jeannie Compiler

Socket.i Socket.java

Java Compiler

Java sources

Network.jar

C Compiler

C sources

Network.dll

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QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Translation Scheme

“1”

“2”

class JavaEnv { int x int z native m1() m2(CEnv) native m3(CEnv) m4(CEnv)}struct CEnv { jint y};Java_C_m1(JEnv)Java_C_m3(JEnv,CEnv)

Jeannie source code Generated code

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2

43

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Typing

• Nested expressions have equivalent types– if (`((jboolean)feof(stdin))) ..;

• Java references are opaque in C– Use in nested Java expression– Assign to variable– Pass as parameter– Return as result

• C can widen Java references– `List lst = `new ArrayList(10);

• C pointers/structs/unions are illegal in Java

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Java Garbage Collection

JNI Jeannie

Localreference

Implicit(do not collect until

control returns to Java)

Global reference

Do not collect until user calls

DeleteGlobalRef

Not supported(just store in Java and use

`x.f)

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Compiler StagesJeannie code

Jeannie AST

Jeannie AST+SymTab

C code Java code

Jeannie Parser

Jeannie Analyzer

Code generator

Jeannie grammar

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Scalable Composition: SyntaxJeannie code

Jeannie AST+SymTab

Jeannie Parser

Code generator

C grammar

Jeannie grammar

Java grammar

Rats!parsergenerator

Jeannie Analyzer

C code Java code

Jeannie AST

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C grammar

Jeannie grammar

Java grammar

Scalable Composition: AnalyzersJeannie code

Jeannie ParserRats!parsergenerator

xtc visitors,commontype rep.Jeannie AST+SymTab

Code generator

C code Java code

C +Jeannie +Java Analyzer

Jeannie AST

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C +Jeannie +Java Analyzer

C grammar

Jeannie grammar

Java grammar

Scalable Composition: CodeGenJeannie code

Jeannie AST

Jeannie AST+SymTab

C AST Java AST

C code Java code

Jeannie Parser

Code generator

C pretty printer Java pretty printer

C stencils Java stencils xtc ASTgenerator

Rats!parsergenerator

xtc visitors,commontype rep.

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FFI Design Goals: Revisited

Productivity– Concise syntax

Safety– Static error checking

Efficiency– See next slide …

Portability– Java virtual machines: HotSpot, J9, Jikes RVM– Operating systems: Mac OS X, Linux, Cygwin

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Efficiency: JNI vs. Jeannie

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

JavaBDD: 11-Queens

JavaBDD: Rubik's Cube

Empty C block in Java

Empty Java block in C

Constant C expr. in Java

Constant Java expr. in C

Exception in C in Java

With array read

With array writeJ9 / Linux

HotSpot / OS X

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• Nested expression is simple:for (i = 0, n = `ja.length; i < n; i++)

s += `ja[`i];

Array Access

• But bulk access is faster:with (jint* ca = `ja) {

jint n = `ja.length;

for (jint i=0; i<n; i++)

s += ca[i];

}

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0 10 20 30 40 50 60 70 80 90

Write

Read

J9 / Linux

HotSpot / OS X

Efficiency:Bulk vs. Simple Array Access

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Related Work

• Improving JNI– Productivity: Bubak+Kurzyniec (Janet)– Safety: Tan et al. (Ccured, ILEA),

Furr+Foster (type inference)– Efficiency: Stepanian et al. (JIT native code)– Portability: Chen et al. (dynamic binary translator)

• Deep language interoperability– XJ, XTATIC, C, Linq, DALI

• Scalable composition– Polyglot, JastAdd, Silver, Stratego/XT, Safari

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Conclusions

• Have:– Language: Jeannie = FFI(Java+C)– Open source compiler contributed to xtc http://cs.nyu.edu/rgrimm/xtc

• Next:– Debugging– Fault isolation– Optimization