LazySetLong.java

import sun.misc.Unsafe;

import java.lang.reflect.Field;

public class LazySetLong {

  static final Unsafe unsafe;
  static final long valueOffset;
  volatile long o;

  static {
    try {
      Field field = Unsafe.class.getDeclaredField("theUnsafe");
      field.setAccessible(true);
      unsafe = (Unsafe) field.get(null);
      valueOffset = unsafe.objectFieldOffset
        (LazySetLong.class.getDeclaredField("o"));
    } catch (Exception e) {
      throw new AssertionError(e);
    }
  }

  /**
   * @param o It is only really useful where the field is volatile, and is thus expected to change unexpectedly.
   * @throws NoSuchFieldException
   */
  public void lazySet(long o) throws NoSuchFieldException {
    unsafe.putOrderedLong(this, valueOffset, o);
  }

  private long callPutOrderedLong(int times) throws NoSuchFieldException {
    final long start = System.nanoTime();
    for (int i = 0; i < times; i++) {
      lazySet(o + 1);
    }
    return System.nanoTime() - start;
  }

  private long setTheVolatileDirectly(int times) {
    final long start = System.nanoTime();
    for (int i = 0; i < times; i++) {
      o++;
    }
    return System.nanoTime() - start;
  }

  public static void main(String... args) throws NoSuchFieldException {
    final LazySetLong that = new LazySetLong();
    for (int i = 0; i < 1000; i++) {
      long time1 = that.callPutOrderedLong(100_000_000);
      long time2 = that.setTheVolatileDirectly(100_000_000);
      System.out.printf("Loop #%,d: callPutOrderedLong() took %.3fus and setting the volatile directly took %.3fus on average, ratio=%.3f%n",
        i, time1 / 1e3, time2 / 1e3, (double) time1 / time2);
    }
    System.out.println("\nJust printing work so that it is not optimized out, work=" + that.o);
  }
}

JMH please.