/*
 * Copyright (c) 2017, Red Hat Inc. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package org.openjdk.gcbench.runtime.cmpxchg;

import org.openjdk.jmh.annotations.*;
import sun.misc.Unsafe;

import java.lang.reflect.Field;
import java.util.concurrent.TimeUnit;

@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Fork(1)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Threads(1)
@State(Scope.Benchmark)
public class WeakCasLoop {

    static final Unsafe U;
    static final long OFF_REF;

    static {
        try {
            Field unsafeField = Unsafe.class.getDeclaredField("theUnsafe");
            unsafeField.setAccessible(true);
            U = (Unsafe) unsafeField.get(null);
            OFF_REF  = U.objectFieldOffset(WeakCasLoop.class.getDeclaredField("ref"));
        } catch (Exception e) {
            throw new AssertionError(e);
        }
    }

    volatile Point ref;

    @Setup
    public void setup() {
        ref = new Point(0, 0);
    }

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void strong() {
        Point ep, np;
        do {
            ep = ref;
            np = ep.next();
        } while (!U.compareAndSwapObject(this, OFF_REF, ep, np));
    }

    public static class Point {
        final int x;
        final int y;

        public Point(int x, int y) {
            this.x = x;
            this.y = y;
        }

        public Point next() {
            return new Point((x + 1) & 255, (y + 2) & 255);
        }
    }

    /*
        i7 4790K, 4.0 Ghz, Linux x86_64, JDK 9 (Shenandoah, 2016-09-05)

            Benchmark         Mode  Cnt   Score   Error  Units

            # Shenandoah
            CasBarriers.test  avgt   25  16.418 ± 0.029  ns/op

            # G1
            CasBarriers.test  avgt   25  12.545 ± 0.041  ns/op

            # Parallel
            CasBarriers.test  avgt   25  12.526 ± 0.030  ns/op

        Analysis pending.
     */

}