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 *
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package org.openjdk.bench.java.util.concurrent;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.TearDown;
import org.openjdk.jmh.annotations.Warmup;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;
import java.util.concurrent.TimeUnit;

/**
 * Benchmark assesses ForkJoinPool performance with dependence on threshold.
 */
@OutputTimeUnit(TimeUnit.MINUTES)
@State(Scope.Benchmark)
@Warmup(iterations = 5, time = 2)
@Measurement(iterations = 5, time = 2)
@Fork(3)
public class ForkJoinPoolThresholdAutoSurplus {

    /**
     * Implementation notes:
     *
     * This test solves the problem with threshold = 1, and adaptive heuristics. The optimal level is static,
     * and lies somewhere in 1..2 interval. Note the test degrades significantly when heuristic starts to fail,
     * and the throughput is buried under FJP overheads.
     *
     * Baseline includes solving problem sequentially. Hence, each test provides the speedup for parallel execution
     * versus sequential version.
     */

    @Param("10000000")
    private int size;

    /** Encapsulate all the state depended on only by actual test. This avoids running baselines for every parameter value. */
    @State(Scope.Benchmark)
    public static class TestState {

        @Param("0")
        private int workers;

        @Param({"1", "2", "3", "4", "5", "6", "7", "8"})
        private int threshold;

        private ForkJoinPool fjp;

        @Setup
        public void setup() {
            if (workers == 0) {
                workers = Runtime.getRuntime().availableProcessors();
            }
            fjp = new ForkJoinPool(workers);
        }

        @TearDown
        public void teardown() {
            fjp.shutdownNow();
        }
    }

    private Problem problem;

    @Setup
    public void setup() {
        problem = new Problem(size);
    }

    @Benchmark
    public long baselineRaw() {
        return problem.solve();
    }

    @Benchmark
    public Long test(TestState state) throws ExecutionException, InterruptedException {
        return state.fjp.invoke(new AutoQueuedTask(state.threshold, problem, 0, problem.size()));
    }

    private static class AutoQueuedTask extends RecursiveTask<Long> {
        private final int thr;
        private final Problem problem;
        private final int l;
        private final int r;

        public AutoQueuedTask(int thr, Problem p, int l, int r) {
            this.thr = thr;
            this.problem = p;
            this.l = l;
            this.r = r;
        }

        @Override
        protected Long compute() {
            if (r - l <= 1 || getSurplusQueuedTaskCount() >= thr) {
                return problem.solve(l, r);
            }

            int mid = (l + r) >>> 1;
            ForkJoinTask<Long> t1 = new AutoQueuedTask(thr, problem, l, mid);
            ForkJoinTask<Long> t2 = new AutoQueuedTask(thr, problem, mid, r);

            t2.fork();

            long res = 0;
            res += t1.invoke();
            res += t2.join();
            return res;
        }
    }
}
