Java 7 Launch Event at LyonJUG, Lyon France. Fork / Join framework and Project Coin.

Java SE 7 Fork / Join FrameworkLanguage Evolutions (Project Coin) Julien Ponge

Fork / Join

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

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

java.util.concurrent executors concurrent queues concurrent collections atomic variables5, 6 synchronization patterns rich locks

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; }}

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());}

1.0 Threads made easy1.11.21.31.4 5 Concurrency made easier 6 7 Parallelism made easier

Sum of an arrayn1 n2 n3 n4 n5 n6 n7 n8 n9 ... ... ... ... sum1 sum2 sum3 sum1 + sum2 sum3 + (...) total sum

A need for divide and conquer

ForkJoinPool Your workThread management SplitMaximize parallelism Fork subtasks Work stealing Join subtasks Compose results

ForkJoinTask join() join() RecursiveAction fork() fork() vs RecursiveTaskChild ForkJoinTask Child ForkJoinTask

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

class FolderSearchTask extends RecursiveTask<Long> {(...) protected Long compute() { long count = 0L; List<RecursiveTask<Long>> forks = new LinkedList<>(); for (Folder subFolder : folder.getSubFolders()) { FolderSearchTask task = new FolderSearchTask(subFolder, searchedWord); forks.add(task); task.fork(); } for (Document document : folder.getDocuments()) { DocumentSearchTask task = new DocumentSearchTask(document, searchedWord); forks.add(task); task.fork(); } for (RecursiveTask<Long> task : forks) { count = count + task.join(); } return count; }(...)}

class FolderSearchTask extends RecursiveTask<Long> {(...) protected Long compute() { long count = 0L; List<RecursiveTask<Long>> forks = new LinkedList<>(); Split for (Folder subFolder : folder.getSubFolders()) { FolderSearchTask task = new FolderSearchTask(subFolder, searchedWord); forks.add(task); task.fork(); } for (Document document : folder.getDocuments()) { DocumentSearchTask task = new DocumentSearchTask(document, searchedWord); forks.add(task); task.fork(); } for (RecursiveTask<Long> task : forks) { count = count + task.join(); } return count; }(...)}

class FolderSearchTask extends RecursiveTask<Long> {(...) protected Long compute() { long count = 0L; List<RecursiveTask<Long>> forks = new LinkedList<>(); for (Folder subFolder : folder.getSubFolders()) { FolderSearchTask task = new FolderSearchTask(subFolder, searchedWord); forks.add(task); } task.fork(); Fork for (Document document : folder.getDocuments()) { DocumentSearchTask task = new DocumentSearchTask(document, searchedWord); forks.add(task); task.fork(); } for (RecursiveTask<Long> task : forks) { count = count + task.join(); } return count; }(...)}

class FolderSearchTask extends RecursiveTask<Long> {(...) protected Long compute() { long count = 0L; List<RecursiveTask<Long>> forks = new LinkedList<>(); for (Folder subFolder : folder.getSubFolders()) { FolderSearchTask task = new FolderSearchTask(subFolder, searchedWord); forks.add(task); task.fork(); } for (Document document : folder.getDocuments()) { DocumentSearchTask task = new DocumentSearchTask(document, searchedWord); forks.add(task); task.fork(); } for (RecursiveTask<Long> task : forks) { count = count + task.join(); } return count; Join, Compose }(...)}

(F/J demo)

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

No I/ONo synchronization / locksDecompose in simple recursive tasksDo not decompose below a thresholdTake advantage of multicores with no painYou have more F/J candidate algorithms thanyou think!

try-with-resources

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

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

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(); } }}

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!

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());}

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()"); }}

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

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)

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)

“Caused by” ≠ “Also happened”

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(); }}

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

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)

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); } }}

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(); } } } }

Not just syntactic sugarClutter-free, correct codeclose(): - 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)

Diamond <>

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

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"));

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"));

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

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

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 classes1 error

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

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

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

Less ceremony when using genericsNo diamond with inner classes

Simpliﬁed varargs

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);}

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>

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

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

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

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

Mark your code as safe for varargsYou can’t cheat with @SafeVaragsRemove @SuppressWarnings in client codeand pay attention to real warnings

Multi-catch & more precise rethrow

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

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();}

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();}

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?

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

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

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!"); }}

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.javaImprecise.java:13: error: exception SomeOtherChildException is never thrown in body ofcorresponding try statement } catch (SomeOtherChildException secondException) { ^1 error

Less clutterBe preciseDo not capture unintended exceptionsBetter exception ﬂow analysis

Minor additions

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

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."); }}

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."); }}

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

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

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Java 7 Launch Event at LyonJUG, Lyon France. Fork / Join framework and Project Coin.

by julien.ponge on Jul 22, 2011

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Java 7 Launch Event at LyonJUG, Lyon France. Fork / Join framework and Project Coin. — Presentation Transcript