org.javasimon.examples.other.SystemTimersPrecision Maven / Gradle / Ivy
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package org.javasimon.examples.other;
import java.util.Map;
import java.util.TreeMap;
/**
* SystemTimersPrecision checks the granularity of both System timers. It counts how many times
* returned values for ms/ns changes and prints the results. Loop is repeated 5 times. After that
* it executes another loop that contains five rapid System.nanoTime() calls assigned to five
* different longs. This is repeated many times (see LOOP constant), although with nanoTime being
* native method it's probably completely pointless. However results are printed 5 times during the
* loop and you can check how well nanoTime call works.
*
* See http://code.google.com/p/javasimon/wiki/SystemTimersGranularity for more.
*
* @author Richard "Virgo" Richter
*/
public final class SystemTimersPrecision {
private static final long LOOP = 10000000;
private static final long MS_RUN = 500;
private SystemTimersPrecision() {
}
/**
* Entry point of the demo application.
*
* @param args command line arguments
*/
public static void main(String[] args) {
for (int round = 1; round <= 5; round++) {
Map deltaMsCount = new TreeMap();
Map deltaNsCount = new TreeMap();
System.out.println("\nRound: " + round);
long msChanges = 0;
long nsChanges = 0;
long initMs = System.currentTimeMillis();
long initNs = System.nanoTime();
long ms = initMs;
long ns = initNs;
for (int i = 0; i < LOOP; i++) {
long newMs = System.currentTimeMillis();
long newNs = System.nanoTime();
if (newMs != ms) {
long delta = newMs - ms;
Integer count = deltaMsCount.get(delta);
if (count == null) {
count = 0;
}
deltaMsCount.put(delta, ++count);
msChanges++;
}
if (newNs != ns) {
long delta = newNs - ns;
Integer count = deltaNsCount.get(delta);
if (count == null) {
count = 0;
}
deltaNsCount.put(delta, ++count);
nsChanges++;
}
ms = newMs;
ns = newNs;
}
System.out.println("msChanges: " + msChanges + " during " + (System.currentTimeMillis() - initMs) + " ms");
System.out.println("deltaMsCount = " + deltaMsCount);
System.out.println("nsChanges: " + nsChanges + " during " + (System.nanoTime() - initNs) + " ns");
System.out.println("deltaNsCount = " + deltaNsCount);
// now something else...
long msCount = 0;
initMs = System.currentTimeMillis();
while (true) {
long newMs = System.currentTimeMillis();
msCount++;
if (newMs - initMs >= MS_RUN) {
break;
}
}
System.out.println("currentTimeMillis msCount = " + msCount);
long nsCount = 0;
initMs = System.nanoTime() / 1000000;
while (true) {
long newMs = System.nanoTime() / 1000000;
nsCount++;
if (newMs - initMs >= MS_RUN) {
break;
}
}
System.out.println("nanoTime msCount = " + nsCount);
System.out.println("Ratio ms/ns: " + msCount / (double) nsCount);
}
for (int round = 1; round <= LOOP; round++) {
long ns1 = System.nanoTime();
long ns2 = System.nanoTime();
long ns3 = System.nanoTime();
long ns4 = System.nanoTime();
long ns5 = System.nanoTime();
if (round % (LOOP / 5) == 0) {
System.out.println("\nns1 = " + ns1);
System.out.println("ns2 = " + ns2 + " (diff: " + (ns2 - ns1) + ")");
System.out.println("ns3 = " + ns3 + " (diff: " + (ns3 - ns2) + ")");
System.out.println("ns4 = " + ns4 + " (diff: " + (ns4 - ns3) + ")");
System.out.println("ns5 = " + ns5 + " (diff: " + (ns5 - ns4) + ")");
}
}
System.out.println();
// last thing - we will count how many nanoTimes in a row will have the same value
for (int round = 1; round <= LOOP; round++) {
long val = System.nanoTime();
int count = 1;
while (val == System.nanoTime()) {
count++;
}
if (round % (LOOP / 5) == 0) {
System.out.println("Change after " + count + " calls");
}
}
}
}