TimerTest.java

/*
 * Copyright 2012, Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.facebook.LinkBench;

import java.util.Random;

import org.junit.Test;

import junit.framework.TestCase;

public class TimerTest extends TestCase {

  @Test
  public void testTimer1() {
    for (int i = 0; i < 100; i++) {
      long wakeTime = System.nanoTime() + i * 1000 * 500;
      Timer.waitUntil(wakeTime);
      long now = System.nanoTime();
      assertTrue(now >= wakeTime);

      // Check that the precision isn't so awful that it would
      // indicate a definite bug (e.g. 100ms)
      assertTrue(now <= wakeTime + 1e7);
    }
  }

  /**
   * Test that we can use the timer to wait for short intervals
   * without getting far behind
   */
  @Test
  public void testTimer2() {
    // Repeatedly wait for 10us

    long waits = 100 * 100; // 100ms total
    long time = System.nanoTime();
    long startTime = time;
    for (int i = 0; i < waits; i++) {
      time += 1e4; // 10 us
      Timer.waitUntil(time);
    }
    long endTime = System.nanoTime();
    System.err.println("took " + ((endTime - startTime) / 1000000) + "ms");
    assertTrue(endTime - startTime >= 1e8);
    assertTrue(endTime - startTime < 1.02e8); // no longer than 102ms
  }

  @Test
  public void testExponentialArrivals() {
    long randSeed = System.currentTimeMillis();
    System.err.println("Random seed: " + randSeed);
    Random rng = new Random(randSeed);

    int trials = 40000;
    int arrivalRate_s = 200000;
    double arrivalRate_ns = arrivalRate_s / (double)1e9;

    // Check that the exponential distribution is creating correct arrival rate.
    long startTime = System.nanoTime();
    long time = startTime;
    for (int i = 0; i < trials; i++) {
      time = Timer.waitExpInterval(rng, time, arrivalRate_ns);
    }
    long endTime = System.nanoTime();

    double actualArrivalRate_ns = trials / (double) (endTime - startTime);
    System.err.println("actual arrival rate: "
         + actualArrivalRate_ns * 1e9 + " /s " +
        " expected " + arrivalRate_s + "/s");

    assertTrue(actualArrivalRate_ns >= arrivalRate_ns * 0.9);
    assertTrue(actualArrivalRate_ns <= arrivalRate_ns * 1.1);
  }
}