State of java.lang.invoke Implementation in OpenJDK

Transcription

1 State of java.lang.invoke Implementation in OpenJDK Vladimir Ivanov HotSpot JVM Compile r Oracle Corp. JVM Language Summit

2 Safe Harbor Statement The following is intended to outline our general product direction. 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 for Oracle s products remains at the sole discretion of Oracle. 2

3 JSR 292 Support for Dynamically Typed Languages in the JVM Initial design sketch 2005 JSR 292 Expert Group formed Expert Group reboot Method Handle API (Early Draft Review) API refinement (e.g., CONSTANT_MethodHandle) Java 7 Release API refinement (e.g., BootstrapMethods) 3

4 Method Handles in JDK 7 GA Good Flexible and powerful. MH graphs are aggressively inlined and optimized. Not-so-good Performance cliff when inlining does not occur MH.invoke() is slow NoClassDefFoundError in large applications Ugly No general fast path for compiled code JVM is entangled in MH operations 4

5 Quest for a Better IR 2012: Lambda Forms in 7u40 Root problem: MH chains are wrong IR for the JVM Lambda Forms for the rescue Mostly-native moves into Java Decouple representation decisions from the JVM Meshes better with the JVM execution engine translates to bytecode Interprets and/or compiles Erases types, avoiding NCDFE issues 5

6 MHs vs LFs A method handle is a typed, directly executable reference to an underlying method, constructor, field, or similar low-level operation, with optional transformations of arguments or return values. [A lambda form is a] symbolic, non-executable form of a method handle's invocation semantics. javadoc public internal MH.form n:1 LF 6

7 The Grand Plan JDK MH.type public n:1 n:1 MT.target CS MH = MethodHandle MT = MethodType CS = CallSite 7

8 JDK public internal The Grand Plan LF MN.form.vmentry MH n:1 n:1.type n:1 extends n:1 MT DMH BMH VM anon classes.target n:1 CS MTF MH = MethodHandle MT = MethodType CS = CallSite LF = LambdaForm DMH = DirectMethodHandle BMH = BoundMethodHandle MN = MemberName MTF = MethodTypeForm 8

9 JDK public internal The Grand Plan LF MN.form.vmentry.vmtarget MH n:1 n:1 n:1.type n:1 extends n:1 MT DMH MH::linkTo* MH::invokeBasic BMH VM anon classes.target n:1 CS MTF MH = MethodHandle MT = MethodType CS = CallSite LF = LambdaForm DMH = DirectMethodHandle BMH = BoundMethodHandle MN = MemberName MTF = MethodTypeForm MHN = MethodHandleNative Upcalls MHN VM calls JVM 9 JVM_Method native stubs appendix resolved_references[] linkcallsite linkmethod etc methodhandles*.cpp MH::init/resolve setcallsitetarget* etc

10 Lambda Form Example: putfield / Lookup.findSetter putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); t6:v=unsafe.putobject((unsafe@...),t4:l,t3:j,t5:l);void} 10

11 Lambda Form Example: putfield / Lookup.findSetter putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); t6:v=unsafe.putobject((unsafe@...),t4:l,t3:j,t5:l);void} Basic value type is one of { ref, int, long, float, double } + void represented as signature letters "LIJFD + V 11

12 Lambda Form Example: putfield / Lookup.findSetter LF.arity = 3 LF.debugName LF.names[7] putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); t6:v=unsafe.putobject((unsafe@...),t4:l,t3:j,t5:l);void} Name.function Name.arguments[] Name.type LF.result = -1 Name.index 12

13 Lambda Form Execution putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); 13

14 Lambda Form Execution MH Entry point: LambdaForm::vmentry interpreter compiled code MH.form LF LF? class (VM anon) Can point to: LambdaForm Interpreter compiled bytecode.vmentry MN.vmtarget JVM_Method.from_interpreted.from_compiled 14

15 Lambda Form Interpreter 15

16 t3:j t4:l t5:l t6:v Lambda Form Compiled Form static void putobjectfieldcast_000( Object, Object, Object ); 0: aload_0 1: invokestatic #16 // DMH.fieldOffset:... 4: lstore_3 5: aload_1 6: invokestatic #20 // DMH.checkBase:... 9: astore 5 11: aload_0 12: aload_2 13: invokestatic #24 // DMH.checkCast:... 16: astore 6 a0:l a1:l a2:l 18: ldc #26 // <<sun.misc.unsafe@3830f1c0>> 20: checkcast #28 // class sun/misc/unsafe 23: aload 5 25: lload_3 26: aload 6 28: invokevirtual #32 // Unsafe.putObject:(Object;Object;)V 31: return putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); t6:v=unsafe.putobject((unsafe@...),t4:l,t3:j,t5:l);void} 16 RuntimeVisibleAnnotations: LambdaForm$Hidden, LambdaForm$Compiled, ForceInline

17 t6:v VM Anonymous Classes Constant Pool Patching static void putobjectfieldcast_000( );... 18: ldc #26 // String CONSTANT_PLACEHOLDER_0 20: checkcast #28 // class sun/misc/unsafe 23: aload 5 25: lload_3 26: aload 6 28: invokevirtual #32 // Unsafe.putObject(...) 31: return putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); t6:v=unsafe.putobject((unsafe@...),t4:l,t3:j,t5:l);void} Unsafe.defineAnonymousClass( LambdaForm.class, byte[] { }, Object[] {, unsafeobj, }) #26 ConstantPool #26 = Utf resolved_references[] {..., unsafeobj,...} 17

18 MHs vs LFs Sharing vs Customization MH Shared Lambda Form many method handles share a single LF instance LF Customized Lambda Form LF instance is customized for some particular method handle MH LF 18

19 MHs vs LFs Example: putfield / Lookup.findSetter LOOKUP.findSetter( MyClass1.class, f1", Field1.class); LOOKUP.findSetter( MyClass2.class, f2", Field2.class); MT MH (MyClass1,Field1)void Field1.class offset1 constructs (MyClass2,Field2)void Field2.class offset2 MH 19 LF.form (L,L,L)void.form putobjectfieldcast_000=lambda(a0:l,a1:l,a2:l)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:l=dmh.checkcast (a0:l,a2:l); t6:v=unsafe.putobject((unsafe@...),t4:l,t3:j,t5:l);void} LF

20 MHs vs LFs Example: putfield / Lookup.findSetter LOOKUP.findSetter( MyClass1.class, i1", int.class); LOOKUP.findSetter( MyClass2.class, l2", long.class); MH MT MH (MyClass1,int)void int.class offset1 constructs (MyClass2,long)void long.class offset2.form (L,L,I)void putintfield_000=lambda(a0:l,a1:l,a2:i)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:v=unsafe.putint((unsafe@...),t4:l,t3:j,a2:i);void} (L,L,J)void.form putlongfield_000=lambda(a0:l,a1:l,a2:j)=>{ t3:j=dmh.fieldoffset (a0:l); t4:l=dmh.checkbase (a1:l); t5:v=unsafe.putlong((unsafe@...),t4:l,t3:j,a2:j);void} LF 20 LF

21 JSR 292 Released 7 GA 7u40 8 GA 8u20 8u40 Lambda Forms Nashorn Project Lambda j.l.i enhancements Type speculation in C2 Math.exact*() intrinsics Lambda Form Sharing 21

22 22

23 Lambda Form Caching 8u40: JEP 210 MH ~10 6 MH LF ~10 6 ~10 3 LF ~10 4 ~10 3 classes classes 23

24 Sharing vs Customization Example: MHs.guardWithTest() 24 T guard(a... a, B... b) { if (test(a...)) return target(a..., b...); else return fallback(a..., b...); } guard=lambda(a0:l, a, b ) => { t1:i =<<test>>(a ); t2:l=mhi.selectalternative( t1:i, <<target>>, <<fallback>>); t3:?=mh.invokebasic(t2:l, a, b );t3}

25 Sharing vs Customization Example: Customized version guard_000=lambda(a0:l)=>{ t1:i t2:l=mhi.selectalternative( t3:v=mh.invokebasic(t2:l);void} test: MethodHandle target: MethodHandle fallback: MethodHandle static void guard_000(object); ldc... // <<MethodHandle()boolean>> checkcast... // class MethodHandle invokevirtual... // MethodHandle.invokeBasic:()I if_icmpne ldc checkcast astore_2 aload_2... // <<MethodHandle()void>>... // class MethodHandle invokevirtual... // MethodHandle.invokeBasic:()V goto ldc... // <<MethodHandle()void>> checkcast... // class MethodHandle astore_2 aload_2 invokevirtual... // MethodHandle.invokeBasic:()V return t1:i t2:l + t3:v 25

26 Sharing vs Customization Example: Shareable version guard_000=lambda(a0:l)=>{ t3:l=bmh$species_l3.argl0(a0:l); // test t4:l=bmh$species_l3.argl1(a0:l); // target t5:l=bmh$species_l3.argl2(a0:l); // fallback t6:i =MethodHandle.invokeBasic(t3:L); t7:l=methodhandleimpl.selectalternative(t6:i,t4:l,t5:l); t8:v=methodhandle.invokebasic(t7:l);void} 26

27 Lambda Form Sharing Pros Smaller dynamic footprint # of loaded classes, Metaspace size Faster startup/warmup less LFs to instantiate, less classes to load, less code to compile Enables new optimizations Lambda Form precompilation Improves worst case stack consumption 27

28 Lambda Form Sharing Dynamic Footprint 16 8 ratio 4 2 metaspace classes 1 Octane 28 higher/better 8u40: b05 vs b21, Nashorn Measurements by Sergey Kuksenko

29 Lambda Form Sharing Startup / Warmup 354% % higher/better 1 st iteration duration 8u40: b05 vs b21, Nashorn

30 Lambda Form Precompilation Before: first 30 invocations go through LF interpreter then compiled to bytecode After: Lambda Form is precompiled during creation completely bypasses LF interpreter 30

31 Stack Consumption Lambda Form Interpreter jdk.nashorn.internal.scripts.script$recompilation$2$test.f1(test.js:1) j.l.i.lambdaform$dmh/ invokestatic_ll_l j.l.i.lambdaform$dmh/ invokespecial_l3_l j.l.i.lambdaform$namedfunction.invoke_lll_l test.js: 1: function f1() {} 2: f1() j.l.i.lambdaform$dmh/ invokestatic_ll_l j.l.i.lambdaform$namedfunction.invokewitharguments j.l.i.lambdaform.interpretname j.l.i.lambdaform.interpretwitharguments j.l.i.lambdaform.interpret_l j.l.i.lambdaform$dmh/ invokespecial_l3_l j.l.i.lambdaform$namedfunction.invoke_lll_l j.l.i.lambdaform$dmh/ invokestatic_ll_l j.l.i.lambdaform$namedfunction.invokewitharguments j.l.i.lambdaform.interpretname j.l.i.lambdaform.interpretwitharguments j.l.i.lambdaform.interpret_l reinvoke exactinvoker j.l.i.lambdaform$mh/ linktocallsite jdk.nashorn.internal.scripts.script$recompilation$1$test.:program(test.js:2) 31

32 Stack Consumption Compiled Form jdk.nashorn.internal.scripts.script$recompilation$2$test.f1(test.js:1) j.l.i.lambdaform$dmh/ invokestatic_ll_l j.l.i.lambdaform$bmh/ reinvoke j.l.i.lambdaform$mh/ exactinvoker j.l.i.lambdaform$mh/ linktocallsite jdk.nashorn.internal.scripts.script$recompilation$1$test.:program(test.js:9) 32

33 Lambda Form Sharing Peak Performance % % higher/better 8u40: b05 vs b21, Nashorn Measurements by Sergey Kuksenko

34 Lambda Form Sharing Problems in 8u40 Profile pollution peak performance suffers Non-constant MH calls became slower JIT can t inline through them less optimized machine code 34

35 Profile Pollution Customization vs Sharing 35

36 Profile Pollution Customized version static void guard_000(object); guard_000=lambda(a0:l)=>{ t1:i =<<test>>(); t2:l=methodhandleimpl.selectalternative( t1:i,<<target>>,<<fallback>>); t3:v=methodhandle.invokebasic(t2:l);void} ldc... // <<test>> checkcast... // class MethodHandle invokevirtual... // MethodHandle.invokeBasic:()I if_icmpne ldc checkcast astore_2 aload_2... // <<target>>... // class MethodHandle invokevirtual... // MH.invokeBasic:()V goto ldc... // <<fallback>> checkcast... // class MethodHandle astore_2 aload_2 invokevirtual... // MethodHandle.invokeBasic:()V return t1:i t2:l + t3:v 36

37 Profile Pollution Customized version static void guard_000(object); 0% guard_000=lambda(a0:l)=>{ t1:i =<<alwaystrue>>(); t2:l=methodhandleimpl.selectalternative( t1:i,<<target>>,<<fallback>>); t3:v=methodhandle.invokebasic(t2:l);void} ldc... // <<alwaystrue>> checkcast... // class MethodHandle invokevirtual... // MH.invokeBasic:()I if_icmpne ldc checkcast astore_2 aload_2... // <<target>>... // class MethodHandle invokevirtual... // MH.invokeBasic:()V goto ldc... // <<fallback>> checkcast... // class MethodHandle astore_2 aload_2 invokevirtual... // MH.invokeBasic:()V return t1:i t2:l + t3:v 37

38 Profile Pollution Customized version static void guard_001(object); 100% guard_001=lambda(a0:l)=>{ t1:i =<<alwaysfalse>>; t2:l=methodhandleimpl.selectalternative( t1:i,<<target>>,<<fallback>>); t3:v=methodhandle.invokebasic(t2:l);void} ldc... // <<alwaysfalse>> checkcast... // class MethodHandle invokevirtual... // MH.invokeBasic:()I if_icmpne ldc checkcast astore_2 aload_2... // <<target>>... // class MethodHandle invokevirtual... // MH.invokeBasic:()V goto ldc... // <<fallback>> checkcast... // class MethodHandle astore_2 aload_2 invokevirtual... // MH.invokeBasic:()V return t1:i t2:l + t3:v 38

39 Profile Pollution Shared version static void guard_000(object);???% aload_0 checkcast // BMH$Species_L3 getfield... // BMH$Species_L3.argL0:Object invokevirtual... // MH.invokeBasic:()I if_icmpne aload_2 checkcast... // class MethodHandle astore_5 aload_5 invokevirtual... // MH.invokeBasic:()V goto aload_3 checkcast... // class MethodHandle astore_5 aload_5 invokevirtual... // MH.invokeBasic:()V return 39

40 Profile Pollution How to fix Idea: customized profiling collect per-methodhandle profile during warm-up inject profile into the JVM when warm-up is over?% static void guard_000(object); aload_0 checkcast // BMH$Species_L3 getfield... // BMH$Species_L3.argL0:Object invokevirtual... // MH.invokeBasic:()I if_icmpne aload_2 checkcast... // class MethodHandle astore_5 aload_5 invokevirtual... // MH.invokeBasic:()V goto aload_3 checkcast... // class MethodHandle astore_5 aload_5 invokevirtual... // MH.invokeBasic:()V return 40

41 Profile Pollution Custom Branch Profiling guard_000=lambda(a0:l)=>{ t1:l=bmh$species_l4.argl0(a0:l); // test t2:l=bmh$species_l4.argl1(a0:l); // target t3:l=bmh$species_l4.argl2(a0:l); // fallback t4:l=bmh$species_l4.argl3(a0:l); // counts (int[2]) t5:i =MethodHandle.invokeBasic(t1:L); t6:i =MethodHandleImpl.profileBoolean(t5:I,t4:L); t7:l=methodhandleimpl.selectalternative(t6:i,t2:l,t3:l); t8:v=methodhandle.invokebasic(t7:l);void} 41

42 Profile Pollution Custom Branch Profiling Logic profiling / warm-up interpreter / C1 C2 when counts array is unknown per-lambdaform compiled method optimized C2 intrinsic injects per-mh counts into IR 42

43 Profile Pollution Custom Branch Profiling Logic profiling / warm-up interpreter / C1 C2 when counts array is unknown per-lambdaform compiled method optimized C2 intrinsic injects per-mh counts into IR 43

44 Profile Pollution Other cases Type profile not a problem Type speculation (by Roland Westrelin in 8u20) -XX:+UseTypeProfile -XX:TypeProfileLevel=[012]{3} Deoptimization counts no generic solution yet fixed some manifestations of the problem JDK : GWT can be marked non-compilable due to deopt count pollution 44

45 Non-Constant Method Handle Invocation MH.invokeExact() et al 45

46 Non-Constant Method Handle Invocation Non-constant method 105 jsr292.gwt::run1 (7 bytes) inline 3 java.lang.invoke.lambdaform$mh/ ::invokeexact_mt (13 bytes) inline 2 java.lang.invoke.invokers::checkexacttype (30 bytes) inline 11 java.lang.invoke.methodhandle::type (5 bytes) 9 java.lang.invoke.methodhandle::invokebasic()v (0 bytes) receiver not constant 46

47 Non-Constant Method Handle Invocation Customized version java.lang.invoke.lambdaform$mh/ ::guard (56 5 java.lang.invoke.lambdaform$dmh/ ::invokestatic I (13 bytes) inline 1 java.lang.invoke.directmethodhandle::internalmembername (8 bytes) inline 9 jsr292.gwt::test1 (12 bytes) inline 31 java.lang.invoke.lambdaform$dmh/ ::invokestatic V (13 bytes) inline 1 java.lang.invoke.directmethodhandle::internalmembername (8 bytes) inline 9 jsr292.gwt::f1 (2 bytes) inline 52 java.lang.invoke.lambdaform$dmh/ ::invokestatic V (13 bytes) inline 1 java.lang.invoke.directmethodhandle::internalmembername (8 bytes) inline 9 jsr292.gwt::f2 (2 bytes) inline (hot) 47

48 Non-Constant Method Handle Invocation Shared version java.lang.invoke.lambdaform$mh/ ::guard (68 24 java.lang.invoke.methodhandle::invokebasic()i (0 bytes) receiver not 47 java.lang.invoke.methodhandle::invokebasic()v (0 bytes) receiver not 64 java.lang.invoke.methodhandle::invokebasic()v (0 bytes) receiver not constant 48

49 Non-Constant Method Handle Invocation Customized Lambda Form single compiled method per MH chain / root LF nmethod Shared Lambda Form compiled method per MH/LF 49

50 Non-Constant Method Handle Invocation Solution: Optional Customization nmethod Original (shared) guard_000=lambda(a0:l)=>{ t1:l=bmh$species_l4.argl0(a0:l); Customized (a0 is overridden by t1:l) guard_000=lambda(a0:l)=>{ t1:l=<<methodhandle >> t2:l=bmh$species_l4.argl0(t1:l); 50

51 Timeline 7 GA 7u40 8 GA 8u20 8u40 8u60 9+ λ-forms Nashorn Project Lambda catchexception λ-form sharing type speculation Math.exact*() intrinsics λ-form sharing Now Aug, 2015 Performance fixes (e.g. per-mh profiling, LF customization) 51

52 Future work Ultimate Sharing MH.asType() Optimization Reduce Stack Consumption Lightweight Code Loading Profile Pollution 52

53 Ultimate Sharing call site LF [ I, J, L,, F ] [ I, J, L,, F ]... Currently: Lambda Form instance per erased signature Goal: Single Lambda Form instance per unit of behavior LF [ I, J, L,, F ] target [ I, J, L,, F ] 53

54 Ultimate Sharing call site No conversions [ I, J, L,, F ] Boxing [ I, J, L,, F ] LF [ I, J, L,, F ] [ L, L, L,, L ] LF [ I, J, L,, F ] [ L, L, L,, L ] target [ I, J, L,, F ] [ I, J, L,, F ] 54

55 Ultimate Sharing call site No conversions Boxing Boxing + VarArgs [ I, J, L,, F ] [ I, J, L,, F ] [ I, J, L,, F ] LF [ I, J, L,, F ] [ L, L, L,, L ] [ L ] LF [ I, J, L,, F ] [ L, L, L,, L ] [ L ] target [ I, J, L,, F ] [ I, J, L,, F ] [ I, J, L,, F ] 55

56 Ultimate Sharing [ I, J, L,, F ] [ I, J, L,, F ] JVM support is needed reliable box/unbox elimination array explosion [ L ] [ ] [ L ] [ ] [ I, J, L,, F ] [ I, J, L,, F ] 56

57 MethodHandle.asType() Better Caching / Sharing Improve caching/sharing of MH.asType() transformations type adaptations are expensive to construct Single-element per-mh cache subject to profile pollution MH.invoke() on shared MH doesn t work well (w.r.t. peak performance) 57

58 Reduce stack consumption Precompiled Lambda Forms jdk.nashorn.internal.scripts.script$recompilation$2$test.f1(test.js:1) j.l.i.lambdaform$dmh/ invokestatic_ll_l j.l.i.lambdaform$bmh/ reinvoke j.l.i.lambdaform$mh/ exactinvoker j.l.i.lambdaform$mh/ linktocallsite jdk.nashorn.internal.scripts.script$recompilation$1$test.:program(test.js:9) 58

59 Reduce stack consumption (1) Lambda Form Inlining jdk.nashorn.internal.scripts.script$recompilation$2$test.f1(test.js:1) j.l.i.lambdaform$dmh/ invokestatic_ll_l j.l.i.lambdaform$bmh/ reinvoke j.l.i.lambdaform$mh/ exactinvoker j.l.i.lambdaform$mh/ linktocallsite j.l.i.lf$mh/.customized jdk.nashorn.internal.scripts.script$recompilation$1$test.:program(test.js:9) 59

60 Reduce stack consumption (1) Lambda Form Inlining jdk.nashorn.internal.scripts.script$recompilation$2$test.f1(test.js:1) j.l.i.lambdaform$mh/ customized j.l.i.lambdaform$mh/ linktocallsite jdk.nashorn.internal.scripts.script$recompilation$1$test.:program(test.js:9) 60

61 Reduce stack consumption (1) Lambda Form Inlining Pros easy to implement doesn t require any JVM extensions Cons defeats Lambda Form sharing too many indy call sites to specialize for VM anonymous classes are too heavyweight 61

62 Reduce stack consumption (2) Tail Calls jdk.nashorn.internal.scripts.script$recompilation$2$test.f1(test.js:1) (*) jdk.nashorn.internal.scripts.script$recompilation$1$test.:program(test.js:9) (*) during invocation: linktocallsite =tail-call=> reinvoke =tail-call=> exactinvoker =tail-call=> invokestatic_ll_l =tail-call=> $test.f1 62

63 Lightweight Code Loading VM Anonymous Classes Class<?> Unsafe.defineAnonymousClass( Class<?> hostclass, byte[] code, Object[] cppatches) 63

64 Lightweight Code Loading VM Anonymous Classes Class<?> Unsafe.defineAnonymousClass( Class<?> hostclass, byte[] code, Object[] cppatches) 64

65 Lightweight Code Loading MethodHandle Lookup.loadCode( /*Class<?> hostclass,*/ byte[] code, Object[] cppatches) 65

66 Profile Pollution MH LF class 66

67 Future Extensions Variable Handles Small API Enhancements Native Calls 67

68 JEP 193: Variable Handles Safe, performant, enhanced atomics access to fields and array elements VarHandles are like method handles for data Abstracts over location static fields, instance fields, arrays, off heap Supports explicit fences and atomic operation Safer than Unsafe, as fast as MethodHandles 68 JEP-193 Variable Handles by Doug Lea, Paul Sandoz

69 API Enhancements Candidates MHs.tryFinally() MHs.*Loop() Lookup.lookupClass()/findSuperConstructor() Additional combinators for argument handling e.g. MHs.spreadArguments(MH target, int pos, int count) discussion 69

70 Native Calls Project Panama: FFI Java Native Construction Lookup.findVirtual() et al Lookup.findNative() Reference (typed) Reference (direct) DirectMethodHandle MemberName NativeMethodHandle NativeEntryPoint Linker MH.linkToVirtual() et al MH.linkToNative() Invocation indy, MH.invoke(), MH.invokeExact() 70 Making native calls from the JVM by John Rose

71 Thank 71

72 Materials Implementation Notes: "Deconstructing MethodHandles by Paul Sandoz "Lambda Forms by John Rose, JVMLS'12 J9's MethodHandle Compilation Pipeline by Dan Heidinga, Jfocus VM Summit

73 Graphic Section Divider 73