Jdk 7 4-forkjoin

JDK 7 출시 기념 (2011.7)JDK 7 소개 #4 ConcurrentyFork & Join (jsr166y)김용환knight76.tistory.comKnight76 at gmail.com1

Multicore-friendly lightweight parallel frameworkJSR166y (maintenance)목적놀고 있는 여러 개의 processor를 최대한 활용을 위해서 디자인됨병렬처리 필요MapReduce와 비슷하지만, 더 세분화할 수 있다. Work-stealing 알고리즘을 기반.3

Fork/JoinForkRecursively큰 단위의 작업을 작은 단위로 쪼갬Join결과를 Recursive하게모음Doug Lee(뉴욕 주립대 교수)http://gee.cs.oswego.edu/dl/papers/fj.pdfhttp://g.oswego.edu/dl/concurrency-interest/4

Map Reduce와 비교Map ReduceNode 기반의 Cluster 기반Single forkFork / Join하나의장비안에서 여러 개의 CPU를 사용하려는 하나의 JVMRecursive forkWork Stealing5

Work StealingCilk에서개념을 채용 (논문)MIT에서 만든 멀티쓰레드 프로그래밍 언어예약어 조금 + C언어(http://supertech.csail.mit.edu/cilk/manual-5.4.6.pdf)특징각 worker 는 DeQueue(double-ended queue)를 가지고 있음 worker가 idle일 때, 바쁜 Worker의 Queue에 쌓인 task 를 steal.왜?여러 개의 processor(core)에서 동작 가능로드 밸런스 (작은 task로 나눌 수 있도록 함)6

Work Stealing7ForkJoinPool클래스에구현되어 있음출처 : http://karlsenchoi.blogspot.com/2011/02/threadpool-work-stealing.html

jsr166y추가된 APIhttp://gee.cs.oswego.edu/dl/jsr166/dist/jsr166ydocs/8

Pseudo code9if (my portion of the work is small enough)dothe work directlyelsesplit my work into two piecesinvokethe two pieces and wait for the results

Java pseudo code 10class OOOTaskextends RecursiveTask { @Override public void compute() {// small enough if (problem.size< THRESHOLD) { // do directlyproblem.solve(); } else {// split Task worker1 = new OOOTask(new Problem(problem.size - 1)); Task worker2 = new OOOTask(new Problem(problem.size- 2));// invokeinvokeAll(worker1, worker2); } }}

예제피보나치 계산Fib(7) 계산CPU는 411

FibonacciProblem12class FibonacciProblem {public int n; public FibonacciProblem(int n) {this.n = n; } public long solve() { return fibonacci(n); } private long fibonacci(int n) {System.out.println("Thread: " + Thread.currentThread().getName() + " calculates " + n); if (n <= 1) { return n;} else {return fibonacci(n - 1) + fibonacci(n - 2); } }}

FibonacciTask13@SuppressWarnings("serial")class FibonacciTask extends RecursiveTask<Long> { private static final intTHRESHOLD = 5; private FibonacciProblem problem; public long result; public FibonacciTask(FibonacciProblem problem) {this.problem = problem; } @Override public Long compute() { if (problem.n < THRESHOLD) { result = problem.solve(); } else {FibonacciTask worker1 = new FibonacciTask( new FibonacciProblem(problem.n - 1));FibonacciTask worker2 = new FibonacciTask( new FibonacciProblem(problem.n - 2));worker1.fork(); result = worker2.compute() + worker1.join(); } return result; }}

Main14public static void main(String[] args) throws Exception {System.out.println("Number of processors: " + Runtime.getRuntime().availableProcessors());intn = 7;StopWatchstopWatch = new StopWatch(); FibonacciProblembigProblem = new FibonacciProblem(n);FibonacciTasktask = new FibonacciTask(bigProblem);ForkJoinPool pool = new ForkJoinPool();pool.invoke(task);long result = task.result;System.out.println("Computed Result: " + result);stopWatch.stop();System.out.println("Elapsed Time: " + stopWatch.getTotalTimeMillis());System.out.println("Steal Count : " + pool.getStealCount());}

실행 결과15No of processors: 4Thread: ForkJoinPool-1-worker-1 calculates 3Thread: ForkJoinPool-1-worker-2 calculates 4Thread: ForkJoinPool-1-worker-3 calculates 4Thread: ForkJoinPool-1-worker-3 calculates 3Thread: ForkJoinPool-1-worker-3 calculates 2Thread: ForkJoinPool-1-worker-3 calculates 1Thread: ForkJoinPool-1-worker-4 calculates 3Thread: ForkJoinPool-1-worker-4 calculates 2Thread: ForkJoinPool-1-worker-4 calculates 1Thread: ForkJoinPool-1-worker-2 calculates 3Thread: ForkJoinPool-1-worker-2 calculates 2Thread: ForkJoinPool-1-worker-1 calculates 2Thread: ForkJoinPool-1-worker-1 calculates 1Thread: ForkJoinPool-1-worker-2 calculates 1Thread: ForkJoinPool-1-worker-4 calculates 0Thread: ForkJoinPool-1-worker-3 calculates 0Thread: ForkJoinPool-1-worker-3 calculates 1Thread: ForkJoinPool-1-worker-4 calculates 1Thread: ForkJoinPool-1-worker-2 calculates 0Thread: ForkJoinPool-1-worker-1 calculates 0Thread: ForkJoinPool-1-worker-2 calculates 1Thread: ForkJoinPool-1-worker-3 calculates 2Thread: ForkJoinPool-1-worker-2 calculates 2Thread: ForkJoinPool-1-worker-1 calculates 1Thread: ForkJoinPool-1-worker-2 calculates 1Thread: ForkJoinPool-1-worker-3 calculates 1Thread: ForkJoinPool-1-worker-3 calculates 0Thread: ForkJoinPool-1-worker-2 calculates 0Thread: ForkJoinPool-1-worker-4 calculates 4Thread: ForkJoinPool-1-worker-4 calculates 3Thread: ForkJoinPool-1-worker-4 calculates 2Thread: ForkJoinPool-1-worker-4 calculates 1Thread: ForkJoinPool-1-worker-4 calculates 0Thread: ForkJoinPool-1-worker-4 calculates 1Thread: ForkJoinPool-1-worker-4 calculates 2Thread: ForkJoinPool-1-worker-4 calculates 1Thread: ForkJoinPool-1-worker-4 calculates 0Computed Result: 13Elapsed Time: 4Steal Count : 4

RecursiveTask & RecursiveAction16FutureForkJoinTaskRecursiveTaskRecursiveAction

API (RecursiveAction)17public abstract class RecursiveAction<V> extends ForkJoinTask<V> { private static final long serialVersionUID = 5232453952276485270L; protected abstract V compute(); public final void getRawResult() { return null; } protected final void setRawResult(V value) { } protected final boolean exec() { compute(); return true; }}

API (RecursiveTask)18public abstract class RecursiveTaskextends ForkJoinTask<Void> { private static final long serialVersionUID = 5232453952276485270L; V result; protected abstract V compute(); public final V getRawResult() { return result; } protected final void setRawResult(V value) { result = value; } protected final boolean exec() { result = compute(); return true; }}

API (ForkJoinPool)20ExecutorExecutorServiceAbstractExecutorServiceForkJoinPool

ThreadLocalRandom멀티쓰레드상에서Random 은 contention과 overhead가 존재. Random 내부에서 thread를 isolation을 함ForkJoinPool에서 Random 사용시 이슈가 속도가 저하되기 때문에 이를 해결할 수 있는 클래스23long f = ThreadLocalRandom.current().nextLong();System.out.println("1 : " + f);f = ThreadLocalRandom.current().nextLong();System.out.println("2 : " + f);1 : 42322372 : 767956431209526212

Phaser특징쓰레드를 동시 시작/종료시킬 수 있도록 함CyclicBarrier와 CountDownLatch클래스를 보다 유연함좋은 자료http://download.oracle.com/javase/7/docs/api/java/util/concurrent/Phaser.htmlhttp://olegignatenko.livejournal.com/16771.html24

Phaser예제25public static void main(String[] args) {runDevelopment(Arrays.asList(new Developer(), new Developer(), new Developer(), new Developer()));}private static void runDevelopment(Iterable<Developer> team) { final Phasermanager = new Phaser(1); //"1" to register selfSystem.out.println("mgr: assign all developers, then start coding"); for (final Developer developer : team) { final String dev = developer.toString();System.out.println("mgr: assigns a new unarrived " + dev + " to the project");manager.register(); new Thread() { public void run() {System.out.println("mgr: " + dev + ", please await all developers");manager.arriveAndAwaitAdvance(); // await all creationSystem.out.println("mgr: " + dev + ", OK to start coding");developer.run();} }.start();}System.out.println("mgr: all assigned, start coding after all arrive");manager.arriveAndDeregister();}class Developer implements Runnable { private final static AtomicIntegeridSource = new AtomicInteger(); private final int id = idSource.incrementAndGet(); public void run() { System.out.println(toString() + ": coding"); } public String toString() { return "developer #" + id; }}

Phaser결과26mgr: assign all developers, then start codingmgr: assigns a new unarrived developer #1 to the projectmgr: assigns a new unarrived developer #2 to the projectmgr: developer #1, please await all developersmgr: assigns a new unarrived developer #3 to the projectmgr: assigns a new unarrived developer #4 to the projectmgr: developer #3, please await all developersmgr: all assigned, start coding after all arrivemgr: developer #4, please await all developersmgr: developer #2, please await all developersmgr: developer #2, OK to start codingdeveloper #2: codingmgr: developer #1, OK to start codingdeveloper #1: codingmgr: developer #3, OK to start codingdeveloper #3: codingmgr: developer #4, OK to start codingdeveloper #4: coding

Jdk 7 4-forkjoin

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Jdk 7 4-forkjoin