jsr166-tests/src/test/java/jsr166/SystemTest.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 * Other contributors include Andrew Wright, Jeffrey Hayes,
 * Pat Fisher, Mike Judd.
 */

package jsr166;

import junit.framework.*;

public class SystemTest extends JSR166TestCase {

    /**
     * Worst case rounding for millisecs; set for 60 cycle millis clock.
     * This value might need to be changed on JVMs with coarser
     * System.currentTimeMillis clocks.
     */
    static final long MILLIS_ROUND = 17;

    /**
     * Nanos between readings of millis is no longer than millis (plus
     * possible rounding).
     * This shows only that nano timing not (much) worse than milli.
     */
    public void testNanoTime1() throws InterruptedException {
        long m1 = System.currentTimeMillis();
        Thread.sleep(1);
        long n1 = System.nanoTime();
        Thread.sleep(SHORT_DELAY_MS);
        long n2 = System.nanoTime();
        Thread.sleep(1);
        long m2 = System.currentTimeMillis();
        long millis = m2 - m1;
        long nanos = n2 - n1;
        assertTrue(nanos >= 0);
        long nanosAsMillis = nanos / 1000000;
        assertTrue(nanosAsMillis <= millis + MILLIS_ROUND);
    }

    /**
     * Millis between readings of nanos is less than nanos, adjusting
     * for rounding.
     * This shows only that nano timing not (much) worse than milli.
     */
    public void testNanoTime2() throws InterruptedException {
        long n1 = System.nanoTime();
        Thread.sleep(1);
        long m1 = System.currentTimeMillis();
        Thread.sleep(SHORT_DELAY_MS);
        long m2 = System.currentTimeMillis();
        Thread.sleep(1);
        long n2 = System.nanoTime();
        long millis = m2 - m1;
        long nanos = n2 - n1;

        assertTrue(nanos >= 0);
        long nanosAsMillis = nanos / 1000000;
        assertTrue(millis <= nanosAsMillis + MILLIS_ROUND);
    }

}