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import java.util.concurrent.Executors; |
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import java.util.concurrent.ExecutorService; |
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import java.util.concurrent.Phaser; |
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import java.util.concurrent.ThreadLocalRandom; |
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import java.util.concurrent.atomic.DoubleAccumulator; |
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import junit.framework.Test; |
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* accumulates by multiple threads produce correct result |
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*/ |
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public void testAccumulateAndGetMT() { |
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final int incs = 1000000; |
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final int nthreads = 4; |
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final ExecutorService pool = Executors.newCachedThreadPool(); |
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DoubleAccumulator a = new DoubleAccumulator(Double::max, 0.0); |
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Phaser phaser = new Phaser(nthreads + 1); |
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for (int i = 0; i < nthreads; ++i) |
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pool.execute(new AccTask(a, phaser, incs)); |
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phaser.arriveAndAwaitAdvance(); |
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phaser.arriveAndAwaitAdvance(); |
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double expected = incs - 1; |
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double result = a.get(); |
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assertEquals(expected, result); |
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pool.shutdown(); |
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} |
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|
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static final class AccTask implements Runnable { |
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final DoubleAccumulator acc; |
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final Phaser phaser; |
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final int incs; |
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volatile double result; |
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AccTask(DoubleAccumulator acc, Phaser phaser, int incs) { |
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this.acc = acc; |
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this.phaser = phaser; |
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this.incs = incs; |
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} |
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|
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public void run() { |
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final DoubleAccumulator acc |
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= new DoubleAccumulator((x, y) -> x + y, 0.0); |
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final int nThreads = ThreadLocalRandom.current().nextInt(1, 5); |
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final Phaser phaser = new Phaser(nThreads + 1); |
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final int incs = 1_000_000; |
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final double total = nThreads * incs/2.0 * (incs - 1); // Gauss |
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final Runnable task = () -> { |
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phaser.arriveAndAwaitAdvance(); |
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DoubleAccumulator a = acc; |
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for (int i = 0; i < incs; ++i) |
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a.accumulate(i); |
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result = a.get(); |
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for (int i = 0; i < incs; i++) { |
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acc.accumulate((double) i); |
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assertTrue(acc.get() <= total); |
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} |
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phaser.arrive(); |
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}; |
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final ExecutorService p = Executors.newCachedThreadPool(); |
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try (PoolCleaner cleaner = cleaner(p)) { |
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for (int i = nThreads; i-->0; ) |
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p.execute(task); |
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phaser.arriveAndAwaitAdvance(); |
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phaser.arriveAndAwaitAdvance(); |
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assertEquals(total, acc.get()); |
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} |
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} |
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