Fork/Join and Project Coin.

1. Java SE 7
JUG SummerCamp 2011
La Rochelle, France

3. Fork / Join
Project Coin
NIO.2
invokedynamic
(...)

4. Fork / Join

5. java.lang.Thread
java.lang.Runnable
wait()
<5 notify()
synchronized

6. Thread thread = new Thread() {
public void run() {
System.out.println(">>> Hello!");
}
};
thread.start();
thread.join();

7. java.util.concurrent
executors
concurrent queues
concurrent collections
atomic variables
5, 6 synchronization patterns
rich locks

8. class Sum implements Callable<Long> {
private final long from;
private final long to;
Sum(long from, long to) {
this.from = from;
this.to = to;
}
public Long call() {
long acc = 0;
for (long i = from; i <= to; i++) {
acc = acc + i;
}
return acc;
}
}

9. ExecutorService executor = Executors.newFixedThreadPool(2);
List<Future<Long>> results = executor.invokeAll(asList(
new Sum(0, 10),
new Sum(100, 1000),
new Sum(10000, 1000000)
));
for (Future<Long> result : results) {
System.out.println(result.get());
}

10. 1.0 Threads made easy
1.1
1.2
1.3
1.4
5 Concurrency made easier
6
7 Parallelism made easier

11. Sum of an array
n1 n2 n3 n4 n5 n6 n7 n8 n9 ... ... ... ...
sum1 sum2 sum3
sum1 + sum2 sum3 + (...)
total sum

12. How many occurrences of
“java.util.List” in this filesystem tree?

13. Load into RAM (1 thread)
Folder
Document
subfolders: List<Folder>
lines: List<String>
documents: List<Document>
Divide & conquer (#cores threads)

14. ForkJoinPool Your work
Thread management Split
Maximize parallelism Fork subtasks
Work stealing Join subtasks
Compose results

15. ForkJoinTask
join() join()
RecursiveAction
fork() fork()
vs
RecursiveTask
Child ForkJoinTask Child ForkJoinTask

16. 16
Folder word
counting task
10
5
1
Document word Document word Folder word
counting task counting task counting task
3 2
fork()
Document word Document word
n join() counting task counting task

17. (F/J demo)

18. Speedup&
7"
6"
5"
4"
3"
2"
1"
2" 4" 6" 8" 10" 12"
#cores

19. No I/O
No synchronization / locks
Decompose in simple recursive tasks
Do not decompose below a threshold
Take advantage of multicores with no pain
You have more F/J candidate algorithms than
you think!

20. try-with-resources

21. private void writeSomeData() throws IOException {
DataOutputStream out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
out.close();
}

22. private void writeSomeData() throws IOException {
DataOutputStream out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
out.close();
}
what if...

23. private void writeSomeData() throws IOException {
DataOutputStream out = null;
try {
out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
} finally {
if (out != null) {
out.close();
}
}
}

24. private void writeSomeData() throws IOException {
DataOutputStream out = null;
try {
out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
} finally {
if (out != null) {
out.close();
}
}
}
...this is still far from correct!

25. try (
FileOutputStream out = new FileOutputStream("output");
FileInputStream in1 = new FileInputStream(“input1”);
FileInputStream in2 = new FileInputStream(“input2”)
) {
// Do something useful with those 3 streams!
// out, in1 and in2 will be closed in any case
out.write(in1.read());
out.write(in2.read());
}

26. public class AutoClose implements AutoCloseable {
@Override
public void close() {
System.out.println(">>> close()");
throw new RuntimeException("Exception in close()");
}
public void work() throws MyException {
System.out.println(">>> work()");
throw new MyException("Exception in work()");
}
}

27. AutoClose autoClose = new AutoClose();
try {
autoClose.work();
} finally {
autoClose.close();
}

28. AutoClose autoClose = new AutoClose();
try {
autoClose.work();
} finally {
autoClose.close();
}
>>> work()
>>> close()
java.lang.RuntimeException: Exception in close()
at AutoClose.close(AutoClose.java:6)
at AutoClose.runWithMasking(AutoClose.java:19)
at AutoClose.main(AutoClose.java:52)

29. AutoClose autoClose = new AutoClose();
try {
autoClose.work();
} finally {
autoClose.close();
}
MyException
m asked by Run
>>> work() time Exception
>>> close()
java.lang.RuntimeException: Exception in close()
at AutoClose.close(AutoClose.java:6)
at AutoClose.runWithMasking(AutoClose.java:19)
at AutoClose.main(AutoClose.java:52)

30. “Caused by” ≠ “Also happened”

31. AutoClose autoClose = new AutoClose();
MyException myException = null;
try {
autoClose.work();
} catch (MyException e) {
myException = e;
throw e;
} finally {
if (myException != null) {
try {
autoClose.close();
} catch (Throwable t) {
myException.addSuppressed(t);
}
} else {
autoClose.close();
}
}

32. AutoClose autoClose = new AutoClose();
MyException myException = null;
try {
autoClose.work();
} catch (MyException e) {
myException = e;
throw e;
} finally {
if (myException != null) {
try {
autoClose.close();
} catch (Throwable t) {
myException.addSuppressed(t);
}
} else {
autoClose.close();
}
}

33. AutoClose autoClose = new AutoClose();
MyException myException = null;
try {
autoClose.work();
} catch (MyException e) {
myException = e;
throw e;
} finally {
if (myException != null) {
try {
autoClose.close();
} catch (Throwable t) {
myException.addSuppressed(t);
}
} else {
autoClose.close();
}
}

34. AutoClose autoClose = new AutoClose();
MyException myException = null;
try {
autoClose.work();
} catch (MyException e) {
myException = e;
throw e;
} finally {
if (myException != null) {
try {
autoClose.close();
} catch (Throwable t) {
myException.addSuppressed(t);
}
} else {
autoClose.close();
}
}

35. AutoClose autoClose = new AutoClose();
MyException myException = null;
try {
autoClose.work();
} catch (MyException e) {
myException = e;
throw e;
} finally {
if (myException != null) {
try {
autoClose.close();
} catch (Throwable t) {
myException.addSuppressed(t);
}
} else {
autoClose.close();
}
}

36. try (AutoClose autoClose = new AutoClose()) {
autoClose.work();
}

37. try (AutoClose autoClose = new AutoClose()) {
autoClose.work();
}
>>> work()
>>> close()
MyException: Exception in work()
at AutoClose.work(AutoClose.java:11)
at AutoClose.main(AutoClose.java:16)
Suppressed: java.lang.RuntimeException: Exception in close()
at AutoClose.close(AutoClose.java:6)
at AutoClose.main(AutoClose.java:17)

38. public void compress(String input, String output)
throws IOException {
try(
FileInputStream fin = new FileInputStream(input);
FileOutputStream fout = new FileOutputStream(output);
GZIPOutputStream out = new GZIPOutputStream(fout)
) {
byte[] buffer = new byte[4096];
int nread = 0;
while ((nread = fin.read(buffer)) != -1) {
out.write(buffer, 0, nread);
}
}
}

39. public void compress(String input, String output) throws IOException { public void compress(String paramString1, String paramString2)
try( throws IOException {
FileInputStream fin = new FileInputStream(input); FileInputStream localFileInputStream = new FileInputStream(paramString1);
FileOutputStream fout = new FileOutputStream(output); Object localObject1 = null;
GZIPOutputStream out = new GZIPOutputStream(fout) try {
) { FileOutputStream localFileOutputStream = new FileOutputStream(paramString2);
byte[] buffer = new byte[4096]; Object localObject2 = null;
int nread = 0; try {
while ((nread = fin.read(buffer)) != -1) { GZIPOutputStream localGZIPOutputStream = new GZIPOutputStream(localFileOutputStream);
out.write(buffer, 0, nread); Object localObject3 = null;
} try {
} byte[] arrayOfByte = new byte[4096];
} int i = 0;
while ((i = localFileInputStream.read(arrayOfByte)) != -1) {
localGZIPOutputStream.write(arrayOfByte, 0, i);
}
} catch (Throwable localThrowable6) {
localObject3 = localThrowable6;
throw localThrowable6;
} finally {
if (localGZIPOutputStream != null) {
if (localObject3 != null) {
try {
localGZIPOutputStream.close();
} catch (Throwable localThrowable7) {
localObject3.addSuppressed(localThrowable7);
}
} else {
localGZIPOutputStream.close();
}
}
}
} catch (Throwable localThrowable4) {
localObject2 = localThrowable4;
throw localThrowable4;
} finally {
if (localFileOutputStream != null) {
if (localObject2 != null) {
try {
localFileOutputStream.close();
} catch (Throwable localThrowable8) {
localObject2.addSuppressed(localThrowable8);
}
} else {
localFileOutputStream.close();
}
}
}
} catch (Throwable localThrowable2) {
localObject1 = localThrowable2;
throw localThrowable2;
} finally {
if (localFileInputStream != null) {
if (localObject1 != null) {
try {
localFileInputStream.close();
} catch (Throwable localThrowable9) {
localObject1.addSuppressed(localThrowable9);
}
} else {
localFileInputStream.close();
}
}
}
}

40. Not just syntactic sugar
Clutter-free, correct code
close():
- be more specific than java.lang.Exception
- no exception if it can’t fail
- no exception that shall not be suppressed
(e.g., java.lang.InterruptedException)

41. Diamond <>

42. List<String> strings = new LinkedList<Integer>();
Map<String, List<String>> contacts =
new HashMap<Integer, String>();

43. List<String> strings = new LinkedList<String>();
strings.add("hello");
strings.add("world");
Map<String, List<String>> contacts = new HashMap<String, List<String>>();
contacts.put("Julien", new LinkedList<String>());
contacts.get("Julien").addAll(asList("Foo", "Bar", "Baz"));

44. List<String> strings = new LinkedList<>();
strings.add("hello");
strings.add("world");
Map<String, List<String>> contacts = new HashMap<>();
contacts.put("Julien", new LinkedList<String>());
contacts.get("Julien").addAll(asList("Foo", "Bar", "Baz"));

45. Map<String, String> map = new HashMap<String, String>() {
{
put("foo", "bar");
put("bar", "baz");
}
};

46. Map<String, String> map = new HashMap<>() {
{
put("foo", "bar");
put("bar", "baz");
}
};

47. Map<String, String> map = new HashMap<>() {
{
put("foo", "bar");
put("bar", "baz");
}
};
Diamond.java:43: error: cannot infer type arguments for HashMap;
Map<String, String> map = new HashMap<>() {
^
reason: cannot use '<>' with anonymous inner classes
1 error

48. class SomeClass<T extends Serializable & CharSequence> { }
Non-denotable type

49. class SomeClass<T extends Serializable & CharSequence> { }
Non-denotable type
SomeClass<?> foo = new SomeClass<String>();
SomeClass<?> fooInner = new SomeClass<String>() { };
SomeClass<?> bar = new SomeClass<>();
SomeClass<?> bar = new SomeClass<>() { };

50. class SomeClass<T extends Serializable & CharSequence> { }
Non-denotable type
SomeClass<?> foo = new SomeClass<String>();
SomeClass<?> fooInner = new SomeClass<String>() { };
SomeClass<?> bar = new SomeClass<>();
SomeClass<?> bar = new SomeClass<>() { };
No denotable type
to generate a class

51. Less ceremony when using generics
No diamond with inner classes

52. Simplified varargs

53. private static <T> void doSomethingBad(List<T> list, T... values) {
values[0] = list.get(0);
}
public static void main(String[] args) {
List list = Arrays.asList("foo", "bar", "baz");
doSomethingBad(list, 1, 2, 3);
}

54. This yields warnings + crash:
private static <T> void doSomethingBad(List<T> list, T... values) {
values[0] = list.get(0);
}
public static void main(String[] args) {
List list = Arrays.asList("foo", "bar", "baz");
doSomethingBad(list, 1, 2, 3);
}
Heap Pollution: List = List<String>

55. private static <T> void doSomethingGood(List<T> list, T... values) {
for (T value : values) {
list.add(value);
}
}

56. private static <T> void doSomethingGood(List<T> list, T... values) {
for (T value : values) {
list.add(value);
}
}
$ javac Good.java
Note: Good.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

57. @SuppressWarnings({“unchecked”,“varargs”})
public static void main(String[] args) {
List<String> list = new LinkedList<>();
doSomethingGood(list, "hi", "there", "!");
}
$ javac Good.java
$

58. static, final methods, constructors
@SafeVarargs
private static <T> void doSomethingGood(List<T> list, T... values) {
for (T value : values) {
list.add(value);
}
}

59. Mark your code as safe for varargs
You can’t cheat with @SafeVarags
Remove @SuppressWarnings in client code
and pay attention to real warnings

60. Multi-catch & more
precise rethrow

61. Class<?> stringClass = Class.forName("java.lang.String");
Object instance = stringClass.newInstance();
Method toStringMethod = stringClass.getMethod("toString");
System.out.println(toStringMethod.invoke(instance));

62. try {
Class<?> stringClass = Class.forName("java.lang.String");
Object instance = stringClass.newInstance();
Method toStringMethod = stringClass.getMethod("toString");
System.out.println(toStringMethod.invoke(instance));
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}

63. try {
Class<?> stringClass = Class.forName("java.lang.String");
Object instance = stringClass.newInstance();
Method toStringMethod = stringClass.getMethod("toString");
System.out.println(toStringMethod.invoke(instance));
} catch (Throwable t) {
t.printStackTrace();
}

64. try {
Class<?> stringClass = Class.forName("java.lang.String");
Object instance = stringClass.newInstance();
Method toStringMethod = stringClass.getMethod("toString");
System.out.println(toStringMethod.invoke(instance));
} catch (Throwable t) {
t.printStackTrace();
}
How about SecurityException?

65. try {
Class<?> stringClass = Class.forName("java.lang.String");
Object instance = stringClass.newInstance();
Method toStringMethod = stringClass.getMethod("toString");
System.out.println(toStringMethod.invoke(instance));
} catch (ClassNotFoundException | InstantiationException |
IllegalAccessException | NoSuchMethodException |
InvocationTargetException e) {
e.printStackTrace();
}
Union of alternatives

66. catch (SomeException e)
Now implicitly final unless assigned...

67. static class SomeRootException extends Exception { }
static class SomeChildException extends SomeRootException { }
static class SomeOtherChildException extends SomeRootException { }
public static void main(String... args) throws Throwable {
try {
throw new SomeChildException();
} catch (SomeRootException firstException) {
try {
throw firstException;
} catch (SomeOtherChildException secondException) {
System.out.println("I got you!");
}
}

68. static class SomeRootException extends Exception { }
static class SomeChildException extends SomeRootException { }
static class SomeOtherChildException extends SomeRootException { }
public static void main(String... args) throws Throwable {
try {
throw new SomeChildException();
} catch (SomeRootException firstException) {
try {
throw firstException;
} catch (SomeOtherChildException secondException) {
System.out.println("I got you!");
}
}
$ javac Imprecise.java
Imprecise.java:13: error: exception SomeOtherChildException is never thrown in body of
corresponding try statement
} catch (SomeOtherChildException secondException) {
^
1 error

69. Less clutter
Be precise
Do not capture unintended exceptions
Better exception flow analysis

70. Minor additions

71. // 123 in decimal, octal, hexadecimal and binary
byte decimal = 123;
byte octal = 0_173;
byte hexadecimal = 0x7b;
byte binary = 0b0111_1011;
// Other values
double doubleValue = 1.111_222_444F;
long longValue = 1_234_567_898L;
long longHexa = 0x1234_3b3b_0123_cdefL;

72. public static boolean isTrue(String str) {
switch(str.trim().toUpperCase()) {
case "OK":
case "YES":
case "TRUE":
return true;
case "KO":
case "NO":
case "FALSE":
return false;
default:
throw new IllegalArgumentException("Not a valid true/false string.");
}
}

73. public static boolean isTrue(String s) {
String str = s.trim().toUpperCase();
int jump = -1;
switch(str.hashCode()) {
case 2404:
if (str.equals("KO")) {
jump = 3; Bucket
}
break;
(...)
switch(jump) {
(...)
case 3:
case 4:
case 5:
return false;
default: Real code
throw new IllegalArgumentException(
"Not a valid true/false string.");
}
}

74. Oracle Technology Network (more soon...)
Fork and Join: Java Can Excel at
Painless Parallel Programming Too!
http://goo.gl/tostz
Better Resource Management with
Java SE 7: Beyond Syntactic Sugar
http://goo.gl/7ybgr

75. Julien Ponge
@jponge
http://gplus.to/jponge
http://julien.ponge.info/
julien.ponge@insa-lyon.fr