Explosion.java

/*
 * Copyright (c) 2014, Oracle and/or its affiliates. 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.
 *
 * 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.
 *
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package org.openjdk.bench.vm.compiler;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.infra.Blackhole;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.concurrent.TimeUnit;

/**
 * Tests that the JVM performs object explosion (or some sort of stack allocation).
 */
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
public class Explosion {

    @Param("5")
    private int len;

    @Benchmark
    public void testHashtableExplosion(Blackhole bh) throws Exception {
        Object o = new Object();
        Object[] oa = new Object[len];
        for (int i = 0; i < len; i++) {
            oa[i] = new Object();
        }

        Hashtable<Object, Object> h = new Hashtable<>();

        for (int i = 0; i < len; i++) {
            h.put(oa[i], o);
        }

        Enumeration<Object> e = h.elements();
        while (e.hasMoreElements()) {
            bh.consume(e.nextElement());
        }
    }
}