/*
 * Copyright (c) 2014, Oracle America, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 *  * Neither the name of Oracle nor the names of its contributors may be used
 *    to endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.openjdk;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;

import java.util.Objects;
import java.util.concurrent.TimeUnit;

@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Fork(3)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
public class NullChecks {

    /*

    TL;DR: Fear not, my little friends, use Objects.requireNonNull.
           Stop using these obfuscating Object.getClass() checks,
           those rely on non-related intrinsic performance, potentially
           not available everywhere.

    Runs are done on i5-4210U, 1.7 GHz, Linux x86_64, JDK 8u40 EA.

    The explanations are derived from studying the generated code
    ("-prof perfasm" is your friend here), the disassembly is skipped
    for brevity.

  ------

    Out of box, C2 compiled:

    Benchmark                  Mode  Cnt  Score   Error  Units
    NullChecks.branch          avgt   25  0.588 ± 0.015  ns/op
    NullChecks.objectGetClass  avgt   25  0.594 ± 0.009  ns/op
    NullChecks.objectsNonNull  avgt   25  0.598 ± 0.014  ns/op

    Object.getClass() is intrinsified.
    Objects.requireNonNull is perfectly inlined.

 ------

    -XX:-Inline, C2 compiled, but no inlining:

    Benchmark                  Mode  Cnt  Score   Error  Units
    NullChecks.branch          avgt   25  2.450 ± 0.020  ns/op
    NullChecks.objectGetClass  avgt   25  2.450 ± 0.010  ns/op
    NullChecks.objectsNonNull  avgt   25  4.433 ± 0.046  ns/op

    This emulates the inlining failure. Highly unlikely in practice,
    given Objects.requireNonNull is a tiny static method. (It is a JDK bug
    otherwise, and should be dealt with, all due cruelty and mayhem
    included)

    Object.getClass ignores the inline settings, and still intrinsifies.
    Objects.requireNonNull pays the cost of additional call.
    All methods also pay the cost for non-inlined @Benchmark method.

 ------

    -XX:TieredStopAtLevel=1, C1 compiled

    Benchmark                  Mode  Cnt  Score   Error  Units
    NullChecks.branch          avgt   25  0.757 ± 0.002  ns/op
    NullChecks.objectGetClass  avgt   25  1.035 ± 0.007  ns/op
    NullChecks.objectsNonNull  avgt   25  0.761 ± 0.008  ns/op

    Object.getClass also intrinsifies, but not that efficiently.
    Objects.requireNonNull inlines and optimizes neatly.

 ------

    -XX:TieredStopAtLevel=1 -XX:-Inline, C1 compiled, no inline

    Benchmark                  Mode  Cnt   Score   Error  Units
    NullChecks.branch          avgt   25   3.233 ± 0.024  ns/op
    NullChecks.objectGetClass  avgt   25  33.877 ± 0.640  ns/op
    NullChecks.objectsNonNull  avgt   25   5.045 ± 0.132  ns/op

    Object.getClass had failed to intrinsify, since C1 stops inlining
    intrinsics with -XX:-Inline -- it calls native jni_GetObjectClass.
    Everything else is in accordance of C2'ish -XX:-Inline.

 ------

    -Xint, interpreter mode

    Benchmark                  Mode  Cnt    Score   Error  Units
    NullChecks.branch          avgt   25  100.733 ± 2.861  ns/op
    NullChecks.objectGetClass  avgt   25  161.147 ± 2.355  ns/op
    NullChecks.objectsNonNull  avgt   25  179.558 ± 5.490  ns/op

    Object.getClass calls into VM. Remarkably, it is still on par
    with Objects.requireNonNull, allegedly because of this:
      https://bugs.openjdk.java.net/browse/JDK-8072070

    ...working around with:

    -Xint -XX:StackShadowPages=1, interpreter mode

    Benchmark                  Mode  Cnt   Score   Error  Units
    NullChecks.branch          avgt   25  30.295 ± 0.090  ns/op
    NullChecks.objectGetClass  avgt   25  83.332 ± 1.181  ns/op
    NullChecks.objectsNonNull  avgt   25  50.637 ± 0.774  ns/op

    Clearly shows the overheads of calling into native getClass.

 ------

     */

    private Object o;

    @Setup
    public void setup() {
        o = new NullChecks();
    }

    @Benchmark
    public void objectGetClass() {
        o.getClass();
    }

    @Benchmark
    public void objectsNonNull() {
        Objects.requireNonNull(o);
    }

    @Benchmark
    public void branch() {
        if (o == null)  {
            throw new NullPointerException();
        }
    }

}