Slide pack for goto java; presentation at JavaZone 2014. The talk looks into the Java compiler and adds support for goto statements.

1. A peek into the OpenJDK
compiler : goto java;
Martin Skarsaune
Java Developer and Co-Owner
高
馬
丁

3. GOTO statements
in Java!

4. GOTO Statement –Objective
• Syntax:
goto identifier;
• Runtime
– Program control moves to target statement
• Other Semantics
– Target (statement label) must be defined in same
scope, compilation error if not
– Potential circular gotos should give compilation
warning.

5. GOTO Statement – Means
1. OpenJDK
– Open source Java implementation
– Compiler implemented in Java
2. Modify compiler source to support goto
statements

6. Success case
public class GotoSuccess {
public static void main(String[] args) {
one: System.out.print("goto ");
two: System.out.print("Java");
goto four;
three: System.out.print("2014");
goto five;
four: System.out.print("Zone ");
goto three;
five: System.out.print("!");
}
}

7. GOTO
AHEAD
Dijkstra 1968:
programmerquality =100 1-
gotos
LoC
æ
è ç
ö
ø ÷

8. What is a
Compiler?
Compiler

9. What is a
Compiler?
front back

10. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

11. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

12. Parse Enter Process Attribute Flow Desugar Generate
• Syntax: goto identifier;
• First convert character stream to token
stream (Scanner.java)
[g][o][t][o][ ][f][o][u][r][;]
GOTO IDENTIFIER SEMI

13. Parse Enter Process Attribute Flow Desugar Generate
• goto is already a reserved word in Java!
• Lucky for us, goto is therefore defined as a
TokenKind.
• Tokens.java:141: GOTO("goto")
• The scanner therefore works out of the box!

14. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
...
import com.sun.tools.javac.parser.Scanner;
...

15. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
scanner.nextToken();

16. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
scanner.nextToken();
assertThat(”First token is GOTO”, scanner.token().kind, is(GOTO));

17. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
scanner.nextToken();
assertThat(”First token is GOTO”, scanner.token().kind, is(GOTO));
scanner.nextToken();

18. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
scanner.nextToken();
assertThat(”First token is GOTO”, scanner.token().kind, is(GOTO));
scanner.nextToken();
assertThat("Second token is IDENTIFIER", scanner.token().kind,
is(IDENTIFIER));

19. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
scanner.nextToken();
assertThat(”First token is GOTO”, scanner.token().kind, is(GOTO));
scanner.nextToken();
assertThat("Second token is IDENTIFIER", scanner.token().kind,
is(IDENTIFIER));
scanner.nextToken();

20. Parse Enter Process Attribute Flow Desugar Generate
final Scanner scanner=factory.newScanner(”goto identifier;”, false);
scanner.nextToken();
assertThat(”First token is GOTO”, scanner.token().kind, is(GOTO));
scanner.nextToken();
assertThat("Second token is IDENTIFIER", scanner.token().kind,
is(IDENTIFIER));
scanner.nextToken();
assertThat("Third token is SEMI", scanner.token().kind, is(SEMI));

21. Parse Enter Process Attribute Flow Desugar Generate Abstract Syntax
CompilationUnit
ClassDefinition
FieldDefintion
MethodDefinition
Signature
Body
IfStatement
Goto
Wikipedia: “the visitor design pattern
is a way of separating an algorithm
from an object structure on which it
operates”
visitClassDef(..)
visitMethodDef(
..)
visitIf(..)
Tree
GOTO IDENTIFIER SEMI
[g][o][t][o][ ][f][o][u][r][;]

22. Parse Enter Process Attribute Flow Desugar Generate
Class Interface

23. Parse Enter Process Attribute Flow Desugar Generate
• Interface based visitors

24. Parse Enter Process Attribute Flow Desugar Generate
• Class based visitors
public void visitGoto(JCGoto tree) {
try {
print("goto " + tree.label + ";");
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
public void visitGoto(JCGoto tree) {
//TODO implement
}

25. Parse Enter Process Attribute Flow Desugar Generate
public class GotoResolver {
Map<GotoTree, Name> gotos;
Map<Name, LabeledStatementTree> targets;
List<StatementTree> statementsInSequence;
...
}
public static class JCLabeledStatement extends JCStatement
implements LabeledStatementTree {
…
public GotoResolver handler;
…
}

26. Parse Enter Process Attribute Flow Desugar Generate
TreeMaker.java:
public JCGoto Goto(Name label, GotoResolver resolver) {
JCGoto tree = new JCGoto(label, resolver);
tree.pos = pos;
return tree;
}
• JavacParser.parseStatement()
case GOTO: {
nextToken();
Name label = ident();
JCGoto t = to(F.at(pos).Goto(label, getGotoResolver()));
accept(SEMI);
return t;
}

27. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

28. Parse Enter Process Attribute Flow Desugar Generate
• Basic sanity testing of compilation unit
– File name and folder location
– Duplicate class names
• Corrections
– Add default constructor if no constructors are
declared

29. Parse Enter Process Attribute Flow Desugar Generate
• Default constructor
public class SimpleClass {
}

30. Parse Enter Process Attribute Flow Desugar Generate
• Default constructor
public class SimpleClass {
public SimpleClass() {
super();
}
}

31. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

32. Parse Enter Process Attribute Flow Desugar Generate
• Annotation processing API
• Part of ordinary javac process since Java 1.6
• Plugin API (see javac documentation)

33. Parse Enter Process Attribute Flow Desugar Generate
• Output controlled by command line switches
@
- proc:none – do not process annotations
- proc:only – only process annotations, do not compile

34. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

35. Parse Enter Process Attribute Flow Desugar Generate
• Semantic checks
– Types
– References
• Corrections
– Add required calls to super constructor

36. Parse Enter Process Attribute Flow Desugar Generate
• We want to verify that goto target exists in
current scope
public class GotoMissingLabel {
public static void main(String[] args) {
one: System.out.print("goto ");
two: System.out.print("Java");
goto six;
three: System.out.print("2014");
goto five;
four: System.out.print("Zone ");
goto three;
five: System.out.print("!");
}
}

37. Parse Enter Process Attribute Flow Desugar Generate
• Attr.java:
@Override
public void visitGoto(JCGoto that) {
that.findTarget();
if(that.target==null)
log.error(that.pos(), "undef.label", that.label);
result = null;
}
class JCGoto:
…
public void findTarget() {
this.target = (JCLabeledStatement)this.handler.findTarget(this);
}

38. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

39. Parse Enter Process Attribute Flow Desugar Generate
Flow analysis
• Detect unreachable code
• Verify assignments
• Ensure proper method return
• Verify (effectively) final
• Check exception flow

40. Parse Enter Process Attribute Flow Desugar Generate
We want to detect circular gotos:
public class GotoCircularWarning {
public static void main(String[] args) {
one: System.out.print("goto ");
two: System.out.print("Java");
goto four;
three: System.out.print("2014");
goto five;
four: System.out.print("Zone ");
goto three;
five: System.out.println("!");
goto one;//forms infinite loop
}
}

41. Parse Enter Process Attribute Flow Desugar Generate
Flow.FlowAnalyzer class:
@Override
public void visitGoto(JCGoto tree) {
if (tree.handler.detectCircularGotoPosition(tree))
log.warning(tree.pos, "circular.goto");
}
compiler.properties:
...
compiler.warn.circular.goto=circular goto
...

42. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

43. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Erase generic types
public class Bridge implements Comparator {
}

44. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Erase generic types
public class Bridge implements Comparator {
}
public interface Comparator<T> {t
int compare(T o1, T o2);
}or<T> {

45. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Erase generic types
public class Bridge implements Comparator<Integer> {
}
public interface Comparator<T> {t
int compare(T o1, T o2);
}or<T> {

46. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Erase generic types
public class Bridge implements Comparator<Integer> {
public int compare(Integer first, Integer second) {
return first - second;
}
}
public interface Comparator<T> {t
int compare(T o1, T o2);
}or<T> {

47. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Erase generic types
public class Bridge implements Comparator {
public int compare(Integer first, Integer second) {
return first - second;
}
}

48. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Erase generic types
public class Bridge implements Comparator {
public int compare(Integer first, Integer second) {
return first - second;
}
/*synthetic*/
public int compare(Object first, Object second) {
return this.compare((Integer)first, (Integer)second);
}
}

49. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Extract Inner Class
public class Outer {
private void foo() { }
public Runnable fooRunner() {
return new Runnable() {
public void run() {
foo();
}
};
}
}

50. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Extract Inner Class
public class Outer {
private void foo() { }
public Runnable fooRunner() {
return new Runnable() {
public void run() {
foo();
}
};
}
}

51. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Extract Inner Class
public class Outer {
private void foo() { }
public Runnable fooRunner() {
return new Outer$1(this);
}
}
class Outer$1 implements Runnable {
final Outer this$0;
public void run() {
this$0.foo();
}
}

52. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Extract Inner Class
public class Outer {
private void foo() { }
public Runnable fooRunner() {
return new Outer$1(this);
}
}
class Outer$1 implements Runnable {
final Outer this$0;
Outer$1(final Outer this$0) {
this.this$0 = this$0;
super();
}
public void run() {
this$0.foo();
}
}

53. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Extract Inner Class
public class Outer {
private void foo() { }
public Runnable fooRunner() {
return new Outer$1(this);
}
}
class Outer$1 implements Runnable {
final Outer this$0;
Outer$1(final Outer this$0) {
this.this$0 = this$0;
super();
}
public void run() {
this$0.foo();
}
}

54. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Extract Inner Class
public class Outer {
private void foo() { }
public Runnable fooRunner() {
return new Outer$1(this);
}
static void access$000(
Outer x0) {
x0.foo();
}
}
class Outer$1 implements Runnable {
final Outer this$0;
Outer$1(final Outer this$0) {
this.this$0 = this$0;
super();
}
public void run() {
Outer.access$000(this$0);
}
}

55. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Boxing
List<Integer> list =
Arrays.asList(1, 2);
for (Integer i : list) {
System.out.println("Double: " + i * 2);
}

56. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Boxing
List<Integer> list =
Arrays.asList(1, 2);
for (Integer i : list) {
System.out.println("Double: " + i * 2);
}
public static <T> List<T> asList(T... a) {
return new ArrayList<>(a);
}

57. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Boxing
List<Integer> list =
Arrays.asList(Integer.valueOf(1), Integer.valueOf(2));
for (Integer i : list) {
System.out.println("Double: " + i * 2);
}

58. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Unboxing
List<Integer> list =
Arrays.asList(Integer.valueOf(1), Integer.valueOf(2));
for (Integer i : list) {
System.out.println("Double: " + i * 2);
}

59. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Unboxing
List<Integer> list =
Arrays.asList(Integer.valueOf(1), Integer.valueOf(2));
for (Integer i : list) {
System.out.println("Double: " + i.intValue() * 2);
}

60. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Varargs
List<Integer> list =
Arrays.asList(Integer.valueOf(1), Integer.valueOf(2));
for (Integer i : list) {
System.out.println("Double: " + i.intValue() * 2);
}

61. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Varargs
List<Integer> list =
Arrays.asList(Integer.valueOf(1), Integer.valueOf(2));
for (Integer i : list) {
System.out.println("Double: " + i.intValue() * 2);
}
public static <T> List<T> asList(T... a) {
return new ArrayList<>(a);
}

62. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Varargs
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (Integer i : list) {
System.out.println("Double: " + i.intValue() * 2);
}

63. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• For each loop
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (Integer i : list) {
System.out.println("Double: " + i.intValue() * 2);
}

64. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• For each loop
public interface Iterable<T> {
Iterator<T> iterator();
}
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (Integer i : list) {
System.out.println("Double: " + i.intValue() * 2);
}
static <T> List<T> asList(T... a) {
return new ArrayList<>(a);
}

65. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• For each loop
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (;;) {
Integer i
System.out.println("Double: " + i.intValue() * 2);
}

66. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• For each loop
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (Iterator i$ = list.iterator();;) {
Integer i
System.out.println("Double: " + i.intValue() * 2);
}

67. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• For each loop
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (Iterator i$ = list.iterator(); i$.hasNext();) {
Integer i
System.out.println("Double: " + i.intValue() * 2);
}

68. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• For each loop
List<Integer> list =
Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2)});
for (Iterator i$ = list.iterator(); i$.hasNext();) {
Integer i = (Integer)i$.next();
System.out.println("Double: " + i.intValue() * 2);
}

69. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enums
public enum Status {
YES, NO, MAYBE
}

70. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enums
public enum Status {
YES, NO, MAYBE
private Status(String $enum$name, int $enum$ordinal) {
super($enum$name, $enum$ordinal);
}
}

71. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enums
public enum Status {
YES, NO, MAYBE
private Status(String $enum$name, int $enum$ordinal) {
super($enum$name, $enum$ordinal);
}
public static Status valueOf(String name) {
return (Status)Enum.valueOf(Status.class, name);
}
}

72. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enums
public enum Status {
YES, NO, MAYBE
private Status(String $enum$name, int $enum$ordinal) {
super($enum$name, $enum$ordinal);
}
public static Status valueOf(String name) {
return (Status)Enum.valueOf(Status.class, name);
}
private static final Status[] $VALUES = new Status[]{
Status.YES, Status.NO, Status.MAYBE};
public static Status[] values() {
return (Status[])$VALUES.clone();
}

73. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enum based switch statements
public class SwitchStatus {
void switchStatus(Status status) {
switch (status) {
case MAYBE:
return;
default:
break;
}
}
}

74. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enum based switch statements
public class SwitchStatus {
void switchStatus(Status status) {
switch (status) {
case MAYBE:
return;
default:
break;
}
}
}

75. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Enum based switch statements
public class SwitchStatus {
void switchStatus(Status status) {
switch (SwitchStatus$1.$SwitchMap$Status[(status).ordinal()]) {
case 1:
return;
default:
break;
}
}
}

76. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
class SwitchStatus$1 {
• Enum based switch statements
public class SwitchStatus {
void switchStatus(Status status) {
switch (SwitchStatus$1.$SwitchMap$Status[(status).ordinal()]) {
case 1:
return;
default:
break;
}
}
}
}

77. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
class SwitchStatus$1 {
static final int[] $SwitchMap$Status = new int[Status.values().length];
• Enum based switch statements
public class SwitchStatus {
void switchStatus(Status status) {
switch (SwitchStatus$1.$SwitchMap$Status[(status).ordinal()]) {
case 1:
return;
default:
break;
}
}
}
}

78. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
class SwitchStatus$1 {
static final int[] $SwitchMap$Status = new int[Status.values().length];
[0][0][0]
• Enum based switch statements
public class SwitchStatus {
void switchStatus(Status status) {
switch (SwitchStatus$1.$SwitchMap$Status[(status).ordinal()]) {
case 1:
return;
default:
break;
}
}
}
}

79. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
class SwitchStatus$1 {
static final int[] $SwitchMap$Status = new int[Status.values().length];
[0][0][1]
static {
• Enum based switch statements
try {
SwitchStatus$1.$SwitchMap$Status[Status.MAYBE.ordinal()] = 1;
} catch public (NoSuchFieldError class SwitchStatus ex) {
{ }
}
}
void switchStatus(Status status) {
switch (SwitchStatus$1.$SwitchMap$Status[(status).ordinal()]) {
case 1:
return;
default:
break;
}
}
}

80. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
class SwitchStatus$1 {
static final int[] $SwitchMap$Status = new int[Status.values().length];
[0][0][1]
static {
• Enum based switch statements
try {
SwitchStatus$1.$SwitchMap$Status[Status.MAYBE.ordinal()] = 1;
} catch public (NoSuchFieldError class SwitchStatus ex) {
{ }
}
}
void switchStatus(Status status) {
switch (SwitchStatus$1.$SwitchMap$Status[(status).ordinal()]) {
case 1:
return;
default:
break;
}
}
}

81. Parse Enter Process Attribute Flow Desugar Generate
processAnnotations(enterTrees(…
parseFiles(…))),…)
…
generate(desugar(flow(attribute(…))))

82. Parse Enter Process Attribute Flow Desugar Generate
• Generate bytecodes
• Organize initializers
• String concatenation
• Some optimizations

83. Parse Enter Process Attribute Flow Desugar Generate
• Organize <init> (Constructor)
public class InstanceInitialization {
String key="key";
String value;
public InstanceInitialization(String value) {
this.value = value;
}
}

84. Parse Enter Process Attribute Flow Desugar Generate
• Organize <init> (Constructor)
public class InstanceInitialization {
String key="key";
String value;
public InstanceInitialization(String value) {
super();
this.value = value;
}
}

85. Parse Enter Process Attribute Flow Desugar Generate
• Organize <init> (Constructor)
public class InstanceInitialization {
String key;
String value;
public InstanceInitialization(String value) {
super();
key = ”key”;
this.value = value;
}
}

86. Parse Enter Process Attribute Flow Desugar Generate
• Organize <init> (Constructor)
public class InstanceInitialization {
String key;
String value;
public <init>(String value) {
super();
key = ”key”;
this.value = value;
}
}

87. Parse Enter Process Attribute Flow Desugar Generate
• Organize <clinit> (Static initialization)
public class StaticInitialization {
static String key="key";
static String value;
static {
value = value;
}
}

88. Parse Enter Process Attribute Flow Desugar Generate
• Organize <clinit> (Static initialization)
public class StaticInitialization {
static String key;
static String value;
static {
key="key”;
value = value;
}
}

89. Parse Enter Process Attribute Flow Desugar Generate
• Organize <clinit> (Static initialization)
public class StaticInitialization {
static String key;
static String value;
static void <clinit>{
key="key”;
value = value;
}
}

90. Parse Enter Process Attribute Flow Desugar Generate
• String concatenation
Source code “Generated code”
”string” + value

91. Parse Enter Process Attribute Flow Desugar Generate
Source code “Generated code”
”string” + value new StringBuilder()

92. Parse Enter Process Attribute Flow Desugar Generate
Source code “Generated code”
”string” + value new StringBuilder()
.append(”string”)

93. Parse Enter Process Attribute Flow Desugar Generate
Source code “Generated code”
”string” + value new StringBuilder()
.append(”string”)
.append(value)

94. Parse Enter Process Attribute Flow Desugar Generate
Source code “Generated code”
”string” + value new StringBuilder()
.append(”string”)
.append(value)
.toString()

95. Goto Generation
• Lucky for us there is a byte code for goto
• goto <addr>

96. Parse Enter Process Attribute Flow Desugar Generate
Source code PC Byte code
…
if (<test>)
{
<ifblock>
}
else
{
<elseblock>
}
<codeafter>
… …
9 ifeq
22
… <elseblock>
… goto
29
<stackmap>
22 <ifblock>
<stackmap>
29 <codeafter>
Code generator (Code.java)
Java >= 1.6:
marked as not alive.
Stack map frames must be
embedded at target of jump
Goto instruction added to list
of pending jumps (Chain.java)
instruction
Pending jumps processed

97. Parse Enter Process Attribute Flow Desugar Generate
• Scenario 1: go back
Source code PC Byte code
…
label: <somecode>
…
goto label;
…
20
<stackmap>
<somecode>
… goto 20
Used by goto?
Must emit stackmap
Emit goto to label and turn
code generation on again

98. Parse Enter Process Attribute Flow Desugar Generate
• Scenario 2: go forward
Source code PC Byte code
Label used?
• emit stack frame
• patch pending gotos
…
goto label;
…
label: <somecode>
…
…
goto
<stackmap>
29 <somecode>
Label position not yet known?
• emit goto
• add to list of pending gotos
• turn generation on again
29

99. Parse Enter Process Attribute Flow Desugar Generate
Gen.java - Labelled
public void visitLabelled(JCLabeledStatement tree) {
// if the label is used from gotos, have to emit stack map
if (tree.handler.isUsed(tree))
code.emitStackMap();
…
}

100. Parse Enter Process Attribute Flow Desugar Generate
Gen.java - Goto
public void visitGoto(JCGoto tree) {
tree.handler.addBranch(new Chain(code.emitJump(goto_), null, code.state.dup()),
tree.target);
//normally goto marks code as not alive, turn generation on
code.entryPoint();
}
Target position known?
• Yes – patch immediately
• No – add to list of pending gotos

101. Mission
Accomplis
hed!

102. ambda

103. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Lambda implementation in Java 8
– Language change
– Compilation
– Runtime support
• Many interesting design considerations

104. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Simple example
public Comparator<String> lambdaExample() {
return (String a, String b) -> a.compareTo(b);
}

105. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• LambdaToMethod.java
public Comparator<String> lambdaExample() {
return (String a, String b) -> a.compareTo(b);
}
/*synthetic*/
private static int
lambda$lambdaExample$0(
,
) {
return ;
}
final String a
final String b
a.compareTo(b)

106. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
public interface Comparator {/*erased*/
• int compare(Runtime
Object o1, Object o2);
}
public Comparator<String> lambdaExample() {
return <invokedynamic>LambdaMetafactory.metafactory(
}
final class LambdaExample$$Lambda$1/1834188994
implements Comparator {
private LambdaExample$$Lambda$1/1834188994()
public int compare(Object,Object)
}
/*synthetic*/
private static int
lambda$lambdaExample$0(
final String a,
final String b) {
return a.compareTo(b);
}
Lookup(LambdaExample), /*caller*/
"compare",
()Comparator, /*MethodType*/
(Object,Object)int, /*MethodType*/
lambda$lambdaExample$0, /*MethodHandle*/
(String,String)int); /*MethodType*/

107. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Runtime class generation
LambdaMetaFactory
• metaFactory(…)
• altMetaFactory(…)
InnerClassLambdaMetafactory
ASM
Lambda Class

108. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Serialization
Lambda
Instance
Serialize
Serialized
Lambda
Lambda
Meta
Factory
Deserialize

109. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Example with instance and local capture
private int c = 3;
public Comparator<String> withInstanceAndLocalCapture() {
int a = 1, b = 2;
return (String d, String e) -> d.compareTo(e) + a + b - c;
}

110. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Example with instance and local capture
private int c = 3;
public Comparator<String> withInstanceAndLocalCapture() {
int a = 1, b = 2;
return (String d, String e) -> d.compareTo(e) + a + b - c;
}
/*synthetic*/
private int lambda$withInstanceAndLocalCapture$1(
final int cap$0, final int cap$1,
final String d, final String e) {
return d.compareTo(e) + cap$0 + cap$1 - c;
}

111. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Example with instance and local capture
private int c = 3;
public Comparator<String> withInstanceAndLocalCapture() {
int a = 1, b = 2;
return <invokedynamic>LambdaMetafactory.metafactory(this,a,b);
}
/*synthetic*/
private int lambda$withInstanceAndLocalCapture$1(
final int cap$0, final int cap$1,
final String d, final String e) {
return d.compareTo(e) + cap$0 + cap$1 - c;
}

112. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Example with instance and local capture
final class LambdaExample$$Lambda$2/2117255219 extends Object implements
Comparator {
public int compare(Object, Object)
private final LambdaExample arg$1;
private final int arg$2;
private final int arg$3;
private LambdaExample$$Lambda$2/2117255219(LambdaExample,int,int)
private static Comparator get$Lambda(LambdaExample,int,int)
}
.lambda$withInstanceAndLocalCapture$1(arg$arg$1 2, arg$3,(String)d,(String)e)

113. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Possible to back port ?
– Capture generated class ?
– Compile time generation of inner class!

114. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Possible to back port ?
– Capture generated class ?
– Compile time generation of inner class!

115. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Step 1: Enable lambda : Source.java
public boolean allowLambda() {
return compareTo( ) >= 0;
}
JDK1_85

116. Parse Enter Process Attribute Flow Desugar Generate
• Step 2: Enable special handling
boolean mustBackportLambda() {
return this.target.compareTo(Target.JDK1_8) < 0;
}
TransTypes Unlambda Lower

117. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Step 3: Implement and call lambda method
if(!this.attr.mustBackportLambda())
result = makeMetafactoryIndyCall(...);
else
{
result = new LambdaBackPorter(...).implementLambdaClass(...);
}

118. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Step 3: Example
private static final class Lambda$$2 implements Comparator<String> {
Lambda$$2 {
super();
}
public int compare(String arg0, String arg1) {
return LambdaExample.lambda$lambdaExample$0(arg0, arg1);
}
public int compare(Object o1, Object o2) {
return this.compare((String)o1, (String)o2);
}
}

119. Parse Enter Process Attribute Flow Desugar Generate
TransTypes Unlambda Lower
• Step 3: Example
public Comparator<String> lambdaExample() {
}
return LnaewmbLdaamMbedta$fa$c2t8o9r(y).;metafactory();

120. ambda

121. Resources
• OpenJDK
– Source: http://hg.openjdk.java.net/
• Compiler hacking tutorial
– http://www.ahristov.com/tutorial/java-compiler.html
• Lambda design discussion
– http://cr.openjdk.java.net/~briangoetz/lambda/lambda-translation.
html
• Sample code:
– https://github.com/skarsaune/goto
• Slide pack:
– http://www.slideshare.net/MartinSkarsaune

122. Questions or
Comments?
Martin Skarsaune
Java Developer and Co-Owner

123. Thank You for
Your Time!
Martin Skarsaune
Java Developer and Co-Owner
if(you.want(nineBot))
goto Kantega;
Kantega:
eat(bbq);
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