org.javasimon.clock.SimonClockUtils Maven / Gradle / Ivy
The newest version!
package org.javasimon.clock;
/**
* Utils related to timers and Clock class, especially default implementation based on system timers
* ({@link SimonClock#SYSTEM}).
*
* @since 3.5
*/
@SuppressWarnings({"UnusedDeclaration"})
public class SimonClockUtils {
/**
* Value of {@link System#nanoTime()} at a particular time, when {@link #INIT_MILLIS} is initialized as well.
* Used in {@link #millisForNano(long)}.
*
* @since 3.3
*/
public static final long INIT_NANOS = Calibration.initNanos;
/**
* Value of {@link System#currentTimeMillis()} at a particular time, when {@link #INIT_NANOS} is initialized as well.
* Used in {@link #millisForNano(long)}.
*
* @since 3.3
*/
public static final long INIT_MILLIS = Calibration.initMillis;
/**
* Measured difference in {@link System#currentTimeMillis()} during calibration.
*
* @since 3.5
*/
public static final long MILLIS_GRANULARITY = Calibration.millisGranularity;
/**
* Average difference in {@link System#nanoTime()} during calibration.
*
* @since 3.5
*/
public static final long NANOS_GRANULARITY = Calibration.nanosGranularity;
/**
* Converts nano timer value into millis timestamp compatible with {@link System#currentTimeMillis()}. Method does not
* just divide nanos by one million, but also works with remembered values for milli- and nano-timers at one particular moment.
*
* @param nanos nano timer value
* @return ms timestamp
* @since 3.3 (moved from SimonManager where it was since 3.1)
*/
public static long millisForNano(long nanos) {
return INIT_MILLIS + (nanos - INIT_NANOS) / SimonClock.NANOS_IN_MILLIS;
}
private static class Calibration {
private static final int NANO_CHANGES = 100;
private static long initNanos;
private static long initMillis;
private static long nanosGranularity;
private static long millisGranularity;
static {
initMillis = System.currentTimeMillis();
long oldNanos;
while (true) {
oldNanos = System.nanoTime();
long nextMillis = System.currentTimeMillis();
if (nextMillis > initMillis) {
millisGranularity = nextMillis - initMillis;
initMillis = nextMillis;
break;
} else {
// this ensures that we should get the last possible nano value before initMillis
initNanos = oldNanos;
}
}
long sumOfNanoDiffs = 0;
int nanoChanges = 0;
int nanoMeasurements = 0;
// we will reuse oldNanos from before
while (nanoChanges < NANO_CHANGES) {
long nextNanos = System.nanoTime();
nanoMeasurements++;
if (nextNanos > oldNanos) {
nanoChanges++;
sumOfNanoDiffs += nextNanos - oldNanos;
oldNanos = nextNanos;
}
}
nanosGranularity = sumOfNanoDiffs / nanoChanges;
/*
Produces funny results when repeated - granularity differences are striking even during a single Maven build:
nanosGranularity = 460 (based on 100 changes and 327 measurements)
nanosGranularity = 1198 (based on 100 changes and 324 measurements)
nanosGranularity = 605 (based on 100 changes and 328 measurements)
System.out.println("nanosGranularity = " + nanosGranularity + " (based on " + nanoChanges + " changes and " + nanoMeasurements + " measurements)");
System.out.println("millisGranularity = " + millisGranularity);
*/
}
}
}