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nigel-v-thomas/App

Created Mar 31, 2013
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Measures the maximum observed drift between the millisecond timer and the nano timer (which will usually be provided by Time Stamp Counter). Src - "The Well-Grounded Java Developer" (Listing 6.1, pg. 165), see related post on java simon google group http://goo.gl/GL4qOR
package uk.me.nvt.PerformanceNanoTimeDrift;
/**
* Measures the maximum observed drift between the millisecond timer and the nano timer
* (which will usually be provided by Time Stamp Counter).
* Src - "The Well-Grounded Java Developer" (Listing 6.1, pg. 165)
*/
public class App {
public static void main(String[] args) {
System.out.println("Hello World!");
runWithSpin(args);
}
private static void runWithSpin(String[] args) {
long nowNanos = 0, startNanos = 0;
long startMillis = System.currentTimeMillis(), nowMillis = startMillis;
int count = 0;
while (startMillis == nowMillis) { // runs at least once, until millisecond has increased
startNanos = System.nanoTime();
nowMillis = System.currentTimeMillis();
++ count;
}
System.out.println("Number of cycles until millisecond increase "+count);
startMillis = nowMillis; // reset startMillis to increment millisecond
double maxDrift = 0;
long lastMillis;
while (true) {
lastMillis = nowMillis;
while (nowMillis - lastMillis < 1000) { // while difference between current and previous is less than 1000
nowNanos = System.nanoTime();
nowMillis = System.currentTimeMillis();
}
long durationMillis = nowMillis - startMillis;
// difference between nanotime (TSC) and millisecond wall clock
double driftNanos = 1000000 * (((double) (nowNanos - startNanos)) / 1000000 - durationMillis);
if (Math.abs(driftNanos) > maxDrift) {
System.out.println("Now - Start = " + durationMillis
+ " driftNanos = " + driftNanos);
maxDrift = Math.abs(driftNanos);
}
}
}
}
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