Building Languages for the JVM - StarTechConf 2011

Building Languages for the JVM Charles Oliver NutterFriday, November 4, 2011

Me • Charles Oliver Nutter • JRuby and JVM guy • “headius” on most services • headius@headius.comFriday, November 4, 2011

Who Was I? • Java EE architect • Successfully! • Never wrote a parser • Never wrote a compiler • But I wanted to learn how...Friday, November 4, 2011

You • Java? • Ruby? • Python? • C#? • Other?Friday, November 4, 2011

Why Create Languages? • Nothing is perfect • New problems need new solutions • Language design can be fun • Fame and fortune? • Not really.Friday, November 4, 2011

Why Impl a Language? • To learn it? • Sort of... • To learn the target platform • Deﬁnitely! • Fame and fortune? • Well...getting there...Friday, November 4, 2011

Challenges • Community • Platform • Speciﬁcations • ResourcesFriday, November 4, 2011

Community • Investment in status quo • Afraid to stand out • Known quantities • Everything else sucks • Gotta get paid!Friday, November 4, 2011

Platform • Matching language semantics • JVM designed around Java • JVM hides underlying platform • Challenging to use • Not bad...C/++ would be way worse • Community may hate it ;-)Friday, November 4, 2011

Speciﬁcations • Incomplete • Ruby had none for years • ...and no complete test suites • Difﬁcult to implement • Low level features • Single-implementation quirks • Hard or impossible to optimizeFriday, November 4, 2011

Resources • You gotta eat • Not much money in language work • Some parts are hard • OSS is a necessityFriday, November 4, 2011

Why JVM? • Because I am lazy • Because VMs are *hard* • Because I can’t be awesome at everythingFriday, November 4, 2011

Ok, Why Really? • Cross-platform • Libraries • Languages • Memory management • Tools • OSSFriday, November 4, 2011

Cross-platform • OpenJDK: Linux, Windows, Solaris, OS X, xBSD • J9: Linux, zLinux, AS/400, ... • HP: OpenVMS, HP/UX, ... • Dalvik (Android): Linux on ARM, x86Friday, November 4, 2011

Libraries • For any need, a dozen libraries • And a couple of them are good! • Cross-platform • Leading edgeFriday, November 4, 2011

Selection of languages • Java • Scala • Clojure • JRuby • Mirah • Jython, Groovy, Fantom, Kotlin, Ceylon, ...Friday, November 4, 2011

Memory management • Best GCs in the world • Fastest object allocation • Safe escape hatches like NIOFriday, November 4, 2011

Tools • Debugging • Proﬁling • Monitoring • JVM internalsFriday, November 4, 2011

Open source? • FOSS reference impl (OpenJDK) • Mostly OSS libraries • Heavy OSS culture • Strong OSS inﬂuence in OpenJDK coreFriday, November 4, 2011

Case Study: JRubyFriday, November 4, 2011

Ruby on the JVM • All of Ruby’s power and beauty • Solid VM underneath • “Just another JVM language”Friday, November 4, 2011

JVM Language • Full interop with Java • Tricky to do... • Very rewarding for 99% case • VM concerns solved • No need to write a GC • No need to write a JIT • ...oh, but wait...Friday, November 4, 2011

More than a JVM language • Use native code where JDK fails us • Paper over ugly bits like CLASSPATH • Matching Ruby semantics exactly* • Push JVM forward too!Friday, November 4, 2011

Playing with JRuby • Simple IRB demo • JRuby on Rails - see Jano’s talk tomorrow • JRuby performance • PotC (???)Friday, November 4, 2011

How did we do it?Friday, November 4, 2011

JRuby Architecture • Parser • Abstract Syntax Tree (AST) • Intermediate Representation (IR) • Core classes • CompilerFriday, November 4, 2011

Parser • Port of MRI’s Bison grammar • “Jay” parser generator for Java • Hand-written lexer • Nearly as fast as the C version • ...once it gets goingFriday, November 4, 2011

system ~/projects/jruby $ jruby -y -e "1 + 1" push state 0 value null reduce tate 0 uncover 0 s rule (1) $$1 : goto from state 0 to 2 push state 2 value null lex tate 2 reading tIDENTIFIER value Token { Value=load, s Position=file:/Users/headius/projects/jruby/lib/jruby.jar!/ jruby/kernel.rb:6} shift from state 2 to 33 push state 33 value Token { Value=load, Position=file:/Users/ headius/projects/jruby/lib/jruby.jar!/jruby/kernel.rb:6} lex tate 33 reading tSTRING_BEG value Token { Value=, s Position=file:/Users/headius/projects/jruby/lib/jruby.jar!/ jruby/kernel.rb:6} reduce tate 33 uncover 2 s rule (487) operation : tIDENTIFIER goto from state 2 to 62 push state 62 value Token { Value=load, Position=file:/Users/ headius/projects/jruby/lib/jruby.jar!/jruby/kernel.rb:6} reduce tate 62 uncover 62 rule (252) $$6 : sFriday, November 4, 2011

system ~/projects/jruby $ jruby -y -e "1 + 1" push state 0 value null reduce tate 0 uncover 0 s rule (1) $$1 : goto from state 0 to 2 push state 2 value null lex tate 2 reading tIDENTIFIER value Token { Value=load, s Position=file:/Users/headius/projects/jruby/lib/jruby.jar!/ jruby/kernel.rb:6} shift from state 2 to 33 You will never need this. push state 33 value Token { Value=load, Position=file:/Users/ headius/projects/jruby/lib/jruby.jar!/jruby/kernel.rb:6} lex tate 33 reading tSTRING_BEG value Token { Value=, s Position=file:/Users/headius/projects/jruby/lib/jruby.jar!/ jruby/kernel.rb:6} reduce tate 33 uncover 2 s rule (487) operation : tIDENTIFIER goto from state 2 to 62 push state 62 value Token { Value=load, Position=file:/Users/ headius/projects/jruby/lib/jruby.jar!/jruby/kernel.rb:6} reduce tate 62 uncover 62 rule (252) $$6 : sFriday, November 4, 2011

public class RubyYaccLexer { public static final Encoding UTF8_ENCODING = UTF8Encoding.INSTANCE; public static final Encoding USASCII_ENCODING = USASCIIEncoding.INSTANCE; public static final Encoding ASCII8BIT_ENCODING = ASCIIEncoding.INSTANCE; private static ByteList END_MARKER = new ByteList(new byte[] {_, E, N, D, _, _}); private static ByteList BEGIN_DOC_MARKER = new ByteList(new byte[] {b, e, g, i, n}); private static ByteList END_DOC_MARKER = new ByteList(new byte[] {e, n, d}); private static final HashMap<String, Keyword> map; static { map = new HashMap<String, Keyword>(); map.put("end", Keyword.END); map.put("else", Keyword.ELSE); map.put("case", Keyword.CASE); map.put("ensure", Keyword.ENSURE); map.put("module", Keyword.MODULE); map.put("elsif", Keyword.ELSIF); map.put("def", Keyword.DEF); map.put("rescue", Keyword.RESCUE); map.put("not", Keyword.NOT); map.put("then", Keyword.THEN); map.put("yield", Keyword.YIELD); map.put("for", Keyword.FOR); map.put("self", Keyword.SELF); map.put("false", Keyword.FALSE);Friday, November 4, 2011

public enum Keyword { END ("end", Tokens.kEND, Tokens.kEND, LexState.EXPR_END), ELSE ("else", Tokens.kELSE, Tokens.kELSE, LexState.EXPR_BEG), CASE ("case", Tokens.kCASE, Tokens.kCASE, LexState.EXPR_BEG), ENSURE ("ensure", Tokens.kENSURE, Tokens.kENSURE, LexState.EXPR_BEG), MODULE ("module", Tokens.kMODULE, Tokens.kMODULE, LexState.EXPR_BEG), ELSIF ("elsif", Tokens.kELSIF, Tokens.kELSIF, LexState.EXPR_BEG), DEF ("def", Tokens.kDEF, Tokens.kDEF, LexState.EXPR_FNAME), RESCUE ("rescue", Tokens.kRESCUE, Tokens.kRESCUE_MOD, LexState.EXPR_MID), NOT ("not", Tokens.kNOT, Tokens.kNOT, LexState.EXPR_BEG), THEN ("then", Tokens.kTHEN, Tokens.kTHEN, LexState.EXPR_BEG), YIELD ("yield", Tokens.kYIELD, Tokens.kYIELD, LexState.EXPR_ARG), FOR ("for", Tokens.kFOR, Tokens.kFOR, LexState.EXPR_BEG), SELF ("self", Tokens.kSELF, Tokens.kSELF, LexState.EXPR_END), FALSE ("false", Tokens.kFALSE, Tokens.kFALSE, LexState.EXPR_END), RETRY ("retry", Tokens.kRETRY, Tokens.kRETRY, LexState.EXPR_END), RETURN ("return", Tokens.kRETURN, Tokens.kRETURN, LexState.EXPR_MID), TRUE ("true", Tokens.kTRUE, Tokens.kTRUE, LexState.EXPR_END), IF ("if", Tokens.kIF, Tokens.kIF_MOD, LexState.EXPR_BEG), DEFINED_P ("defined?", Tokens.kDEFINED, Tokens.kDEFINED, LexState.EXPR_ARG),Friday, November 4, 2011

private int yylex() throws IOException { int c; boolean spaceSeen = false; boolean commandState; if (lex_strterm != null) { int tok = lex_strterm.parseString(this, src); if (tok == Tokens.tSTRING_END || tok == Tokens.tREGEXP_END) { lex_strterm = null; setState(LexState.EXPR_END); } return tok; } commandState = commandStart; commandStart = false; loop: for(;;) { c = src.read(); switch(c) {Friday, November 4, 2011

case <: return lessThan(spaceSeen); case >: return greaterThan(); case ": return doubleQuote(); case `: return backtick(commandState); case : return singleQuote(); case ?: return questionMark(); case &: return ampersand(spaceSeen); case |: return pipe(); case +: return plus(spaceSeen);Friday, November 4, 2011

private int lessThan(boolean spaceSeen) throws IOException { int c = src.read(); if (c == < && lex_state != LexState.EXPR_DOT && lex_state != LexState.EXPR_CLASS && !isEND() && (!isARG() || spaceSeen)) { int tok = hereDocumentIdentifier(); if (tok != 0) return tok; } determineExpressionState(); switch (c) { case =: if ((c = src.read()) == >) { yaccValue = new Token("<=>", getPosition()); return Tokens.tCMP;Friday, November 4, 2011

%% program : { lexer.setState(LexState.EXPR_BEG); support.initTopLocalVariables(); } top_compstmt { // ENEBO: Removed !compile_for_eval which probably is to reduce warnings if ($2 != null) { /* last expression should not be void */ if ($2 instanceof BlockNode) { support.checkUselessStatement ($<BlockNode>2.getLast()); } else { support.checkUselessStatement($2); } } support.getResult().setAST(support.addRootNode ($2, support.getPosition($2))); }Friday, November 4, 2011

stmt : kALIAS fitem { lexer.setState(LexState.EXPR_FNAME); } fitem { $$ = support.newAlias($1.getPosition(), $2, $4); } | kALIAS tGVAR tGVAR { $$ = new VAliasNode($1.getPosition(), (String) $2.getValue(), (String) $3.getValue()); } | kALIAS tGVAR tBACK_REF { $$ = new VAliasNode($1.getPosition(), (String) $2.getValue(), "$" + $<BackRefNode>3.getType()); } | kALIAS tGVAR tNTH_REF { support.yyerror("cant make alias for the number variables"); } | kUNDEF undef_list { $$ = $2; } | stmt kIF_MOD expr_value { $$ = new IfNode(support.getPosition($1), support.getConditionNode($3), $1, null); }Friday, November 4, 2011

public Object yyparse (RubyYaccLexer yyLex) throws java.io.IOException { if (yyMax <= 0) yyMax = 256;"" " // initial size int yyState = 0, yyStates[] = new int[yyMax];" // state stack Object yyVal = null, yyVals[] = new Object[yyMax];" // value stack int yyToken = -1;" " " " " // current input int yyErrorFlag = 0;" " " " // #tokens to shift yyLoop: for (int yyTop = 0;; ++ yyTop) { if (yyTop >= yyStates.length) {" " " // dynamically increase int[] i = new int[yyStates.length+yyMax]; System.arraycopy(yyStates, 0, i, 0, yyStates.length); yyStates = i; Object[] o = new Object[yyVals.length+yyMax]; System.arraycopy(yyVals, 0, o, 0, yyVals.length); yyVals = o; } yyStates[yyTop] = yyState; yyVals[yyTop] = yyVal; if (yydebug != null) yydebug.push(yyState, yyVal);Friday, November 4, 2011

if (state == null) { yyVal = yyDefault(yyV > yyTop ? null : yyVals[yyV]); } else { yyVal = state.execute(support, lexer, yyVal, yyVals, yyTop); }Friday, November 4, 2011

states[23] = new ParserState() { public Object execute(ParserSupport support, RubyYaccLexer lexer, Object yyVal, Object[] yyVals, int yyTop) { yyVal = new IfNode(support.getPosition(((Node)yyVals [-2+yyTop])), support.getConditionNode(((Node)yyVals[0+yyTop])), ((Node) yyVals[-2+yyTop]), null); return yyVal; } }; Never look at this. states[24] = new ParserState() { public Object execute(ParserSupport support, RubyYaccLexer lexer, Object yyVal, Object[] yyVals, int yyTop) { yyVal = new IfNode(support.getPosition(((Node)yyVals [-2+yyTop])), support.getConditionNode(((Node)yyVals[0+yyTop])), null, ((Node)yyVals[-2+yyTop])); return yyVal; } };Friday, November 4, 2011

AST • Interpreted directly • Specialized in places • Large and richFriday, November 4, 2011

$ ast -e "a = true; if a; 2; else; 3; end" AST: RootNode 0 BlockNode 0 NewlineNode 0 LocalAsgnNode:a 0 TrueNode:true 0 NewlineNode 0 IfNode 0 LocalVarNode:a 0 NewlineNode 0 FixnumNode 0 NewlineNode 0 FixnumNode 0Friday, November 4, 2011

public class IfNode extends Node { private final Node condition; private final Node thenBody; private final Node elseBody; public IfNode(ISourcePosition position, Node condition, Node thenBody, Node elseBody) { super(position); assert condition != null : "condition is not null"; // assert thenBody != null : "thenBody is not null"; // assert elseBody != null : "elseBody is not null"; this.condition = condition; this.thenBody = thenBody; this.elseBody = elseBody; }Friday, November 4, 2011

@Override public IRubyObject interpret(Ruby runtime, ThreadContext context, IRubyObject self, Block aBlock) { ISourcePosition position = getPosition(); context.setFile(position.getFile()); context.setLine(position.getStartLine()); IRubyObject result = condition.interpret(runtime, context, self, aBlock); if (result.isTrue()) { return thenBody == null ? runtime.getNil() : thenBody.interpret(runtime, context, self, aBlock); } else { return elseBody == null ? runtime.getNil() : elseBody.interpret(runtime, context, self, aBlock); } }Friday, November 4, 2011

IR (future work) • Control ﬂow graph • Ruby-speciﬁc instruction set • Optimizing compiler • Ruby-level optimizationsFriday, November 4, 2011

jruby -e “1 + 1”Friday, November 4, 2011

2011-11-04T05:23:09.375-03:00: IR_Printer: instrs: 0 %self = recv_self 1 %block(0:0) = recv_closure 2 file_name(-e) 3 line_num(0) 4 %v_0 = call(+, 1:fixnum, [1:fixnum]) 5 return(%v_0) 2011-11-04T05:23:09.375-03:00: IR_Printer: live variables: %v_0: 4-5Friday, November 4, 2011

a = 1; while a < 10; puts a; a += 1; endFriday, November 4, 2011

2011-11-04T05:25:23.517-03:00: IR_Printer: instrs: 0 %self = recv_self 1 %block(0:0) = recv_closure 2 file_name(-e) 3 line_num(0) 4 a(0:1) = 1:fixnum 5 _LOOP_BEGIN_0: 6 %v_1 = call(<, a(0:1), [10:fixnum]) 7 beq(%v_1, true, _ITER_BEGIN_0) 8 %v_0 = nil 9 jump _LOOP_END_0 10 _ITER_BEGIN_0: 11 %v_2 = call(puts, %self, [a(0:1)]) 12 %v_3 = call(+, a(0:1), [1:fixnum]) 13 a(0:1) = copy(%v_3) 14 %v_0 = copy(%v_3) 15 thread_poll 16 _ITER_END_0: 17 jump _LOOP_BEGIN_0 18 _LOOP_END_0: 19 return(%v_0) 2011-11-04T05:25:23.517-03:00: IR_Printer: live variables: %v_0: 8-19 %v_1: 6-7 %v_3: 12-14Friday, November 4, 2011

2011-11-04T05:25:23.518-03:00: IRScope: ################## After CFG Linearize################## 2011-11-04T05:25:23.518-03:00: IR_Printer: ---------------------------------------- 2011-11-04T05:25:23.518-03:00: IR_Printer: Method [root]: [script]:-e 2011-11-04T05:25:23.518-03:00: IR_Printer: Graph: BB [4:LBL_3]:>[7], <[3] BB [1:LBL_1]:>[8,2] BB [2:LBL_2]:>[3], <[1] BB [7:_LOOP_END_0]:>[8], <[4] BB [8:LBL_4]:<[1,7] BB [3:_LOOP_BEGIN_0]:>[5,4], <[6,2] BB [6:_ITER_END_0]:>[3], <[5] BB [5:_ITER_BEGIN_0]:>[6], <[3]Friday, November 4, 2011

2011-11-04T05:25:23.517-03:00: IR_Printer: instrs: 0 %self = recv_self 1 %block(0:0) = recv_closure 2 file_name(-e) 3 line_num(0) 4 a(0:1) = 1:fixnum 5 _LOOP_BEGIN_0: 6 %v_1 = call(<, a(0:1), [10:fixnum]) 7 beq(%v_1, true, _ITER_BEGIN_0) 8 %v_0 = nil 9 jump _LOOP_END_0 10 _ITER_BEGIN_0: 11 %v_2 = call(puts, %self, [a(0:1)]) 12 %v_3 = call(+, a(0:1), [1:fixnum]) 13 a(0:1) = copy(%v_3) 14 %v_0 = copy(%v_3) 15 thread_poll 16 _ITER_END_0: 17 jump _LOOP_BEGIN_0 18 _LOOP_END_0: 19 return(%v_0) 2011-11-04T05:25:23.517-03:00: IR_Printer: live variables: %v_0: 8-19 %v_1: 6-7 %v_3: 12-14Friday, November 4, 2011

2011-11-04T05:25:23.518-03:00: IR_Printer: Instructions: BB [4:LBL_3] %v_0 = nil BB [1:LBL_1] BB [2:LBL_2] %self = recv_self %block(0:0) = recv_closure file_name(-e) line_num(0) a(0:1) = 1:fixnum BB [7:_LOOP_END_0] return(%v_0) BB [8:LBL_4] return(nil)Friday, November 4, 2011

Core classes • Mostly Java-based • Leverage JDK where possible • Work around JDK where necessary • Use Ruby when possibleFriday, November 4, 2011

@JRubyClass(name="Fixnum", parent="Integer", include="Precision") public class RubyFixnum extends RubyInteger { public static RubyClass createFixnumClass(Ruby runtime) { RubyClass fixnum = runtime.defineClass("Fixnum", runtime.getInteger(), ObjectAllocator.NOT_ALLOCATABLE_ALLOCATOR);Friday, November 4, 2011

@JRubyMethod(name = "+") public IRubyObject op_plus(ThreadContext context, IRubyObject other) { if (other instanceof RubyFixnum) { return addFixnum(context, (RubyFixnum)other); } return addOther(context, other); }Friday, November 4, 2011

private IRubyObject addFixnum(ThreadContext context, RubyFixnum other) { long otherValue = other.value; long result = value + otherValue; if (additionOverflowed(value, otherValue, result)) { return addAsBignum(context, other); } return newFixnum(context.getRuntime(), result); }Friday, November 4, 2011

Compiler • AST-walking • ASM bytecode library • Minimal optimizations • Invokedynamic really helps • IR offers new opportunitiesFriday, November 4, 2011

jruby --bytecode -e “1 + 1”Friday, November 4, 2011

ALOAD 0 INVOKEVIRTUAL ruby/__dash_e__.getCallSite0 ALOAD 1 ALOAD 2 ALOAD 1 GETFIELD org/jruby/runtime/ThreadContext.runtime INVOKESTATIC org/jruby/RubyFixnum.one LDC 1 INVOKEVIRTUAL org/jruby/runtime/CallSite.call ARETURNFriday, November 4, 2011

public class ASTCompiler { private boolean isAtRoot = true; public void compileBody(Node node, BodyCompiler context, boolean expr) { Node oldBodyNode = currentBodyNode; currentBodyNode = node; compile(node, context, expr); currentBodyNode = oldBodyNode; } public void compile(Node node, BodyCompiler context, boolean expr) { if (node == null) { if (expr) context.loadNil(); return; } switch (node.getNodeType()) { case ALIASNODE: compileAlias((AliasNode) node, context, expr); break; case ANDNODE: compileAnd(node, context, expr); break;Friday, November 4, 2011

public void compileIf(Node node, BodyCompiler context, final boolean expr) { final IfNode ifNode = (IfNode) node; // optimizations if we know ahead of time it will always be true or false Node actualCondition = ifNode.getCondition(); while (actualCondition instanceof NewlineNode) { actualCondition = ((NewlineNode)actualCondition).getNextNode(); } if (actualCondition.getNodeType().alwaysTrue()) { // compile condition as non-expr and just compile "then" body compile(actualCondition, context, false); compile(ifNode.getThenBody(), context, expr); } else if (actualCondition.getNodeType().alwaysFalse()) { // always false or nil compile(ifNode.getElseBody(), context, expr); } else {Friday, November 4, 2011

BranchCallback trueCallback = new BranchCallback() { public void branch(BodyCompiler context) { if (ifNode.getThenBody() != null) { compile(ifNode.getThenBody(), context, expr); } else { if (expr) context.loadNil(); } } }; BranchCallback falseCallback = new BranchCallback() { public void branch(BodyCompiler context) { if (ifNode.getElseBody() != null) { compile(ifNode.getElseBody(), context, expr); } else { if (expr) context.loadNil(); } } }; // normal compile(actualCondition, context, true); context.performBooleanBranch(trueCallback, falseCallback); }Friday, November 4, 2011

public abstract class BaseBodyCompiler implements BodyCompiler { protected SkinnyMethodAdapter method; protected VariableCompiler variableCompiler; protected InvocationCompiler invocationCompiler; protected int argParamCount; protected Label[] currentLoopLabels; protected Label scopeStart = new Label(); protected Label scopeEnd = new Label(); protected Label redoJump; protected boolean inNestedMethod = false; private int lastLine = -1; private int lastPositionLine = -1; protected StaticScope scope; protected ASTInspector inspector; protected String methodName; protected String rubyName; protected StandardASMCompiler script;Friday, November 4, 2011

public void performBooleanBranch(BranchCallback trueBranch, BranchCallback falseBranch) { Label afterJmp = new Label(); Label falseJmp = new Label(); // call isTrue on the result isTrue(); method.ifeq(falseJmp); // EQ == 0 (i.e. false) trueBranch.branch(this); method.go_to(afterJmp); // FIXME: optimize for cases where we have no false branch method.label(falseJmp); falseBranch.branch(this); method.label(afterJmp); }Friday, November 4, 2011

More Demos! • JRuby + JVM ﬂags • JRuby concurrency • Invokedynamic (Java 7) • Redcar Editor • Ruboto (Android) • VisualVMFriday, November 4, 2011

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Building Languages for the JVM - StarTechConf 2011

by Charles Nutter

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