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Utility classes for Jetty
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//
// ========================================================================
// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//

package org.eclipse.jetty.util;

import java.util.concurrent.TimeUnit;

/**
 * Utility class with methods that deal with {@link System#nanoTime()}.
 */
public class NanoTime
{
    /**
     * @return the current nanoTime via {@link System#nanoTime()}
     */
    public static long now()
    {
        return System.nanoTime();
    }

    /**
     * Calculates the nanoseconds elapsed between two nanoTimes.
     *
     * @param beginNanoTime the begin nanoTime
     * @param endNanoTime the end nanoTime
     * @return the nanoseconds elapsed
     */
    public static long elapsed(long beginNanoTime, long endNanoTime)
    {
        return endNanoTime - beginNanoTime;
    }

    /**
     * Calculates the nanoseconds elapsed since a begin nanoTime and the current nanoTime.
     *
     * @param beginNanoTime the begin nanoTime
     * @return the nanoseconds elapsed since the given begin nanoTime and the current nanoTime
     */
    public static long since(long beginNanoTime)
    {
        return elapsed(beginNanoTime, now());
    }

    /**
     * Calculates the nanoseconds remaining from the current nanoTime until an end nanoTime.
     *
     * @param endNanoTime the end nanoTime
     * @return the nanoseconds remaining from the current nanoTime until the given end nanoTime
     */
    public static long until(long endNanoTime)
    {
        return elapsed(now(), endNanoTime);
    }

    /**
     * Calculates the milliseconds elapsed between two nanoTimes.
     *
     * @param beginNanoTime the begin nanoTime
     * @param endNanoTime the end nanoTime
     * @return the milliseconds elapsed
     */
    public static long millisElapsed(long beginNanoTime, long endNanoTime)
    {
        return TimeUnit.NANOSECONDS.toMillis(elapsed(beginNanoTime, endNanoTime));
    }

    /**
     * Calculates the milliseconds elapsed between a begin nanoTime and the current nanoTime.
     *
     * @param beginNanoTime the begin nanoTime
     * @return the milliseconds elapsed between the given begin nanoTime and the current nanoTime
     */
    public static long millisSince(long beginNanoTime)
    {
        return millisElapsed(beginNanoTime, now());
    }

    /**
     * Calculates the milliseconds remaining between the current nanoTime and an end nanoTime.
     *
     * @param endNanoTime the end nanoTime
     * @return the milliseconds remaining between the current nanoTime and the given end nanoTime
     */
    public static long millisUntil(long endNanoTime)
    {
        return millisElapsed(now(), endNanoTime);
    }

    /**
     * Calculates the seconds elapsed between two nanoTimes.
     *
     * @param beginNanoTime the begin nanoTime
     * @param endNanoTime the end nanoTime
     * @return the seconds elapsed
     */
    public static long secondsElapsed(long beginNanoTime, long endNanoTime)
    {
        return TimeUnit.NANOSECONDS.toSeconds(elapsed(beginNanoTime, endNanoTime));
    }

    /**
     * Calculates the seconds elapsed between a begin nanoTime and the current nanoTime.
     *
     * @param beginNanoTime the begin nanoTime
     * @return the seconds elapsed between the given begin nanoTime and the current nanoTime
     */
    public static long secondsSince(long beginNanoTime)
    {
        return secondsElapsed(beginNanoTime, now());
    }

    /**
     * Calculates the seconds remaining between the current nanoTime and an end nanoTime.
     *
     * @param endNanoTime the end nanoTime
     * @return the seconds remaining between the current nanoTime and the given end nanoTime
     */
    public static long secondsUntil(long endNanoTime)
    {
        return secondsElapsed(now(), endNanoTime);
    }

    /**
     * Returns whether the first nanoTime is strictly before the second nanoTime.
     * Reads as: {@code "is nanoTime1 strictly before nanoTime2?"}.
     * Avoids the common mistake of comparing the 2 nanoTimes with the
     * less-than {@code <} operator, which cannot be used when comparing nanoTimes,
     * as specified in {@link System#nanoTime()}.
     *
     * @param nanoTime1 the first nanoTime
     * @param nanoTime2 the second nanoTime
     * @return whether the first nanoTime is strictly before the second nanoTime
     * @see #isBeforeOrSame(long, long)
     */
    public static boolean isBefore(long nanoTime1, long nanoTime2)
    {
        return nanoTime1 - nanoTime2 < 0;
    }

    /**
     * Returns whether the first nanoTime is before or the same as the second nanoTime.
     *
     * @param nanoTime1 the first nanoTime
     * @param nanoTime2 the second nanoTime
     * @return whether the first nanoTime is before or the same as the second nanoTime
     * @see #isBefore(long, long)
     */
    public static boolean isBeforeOrSame(long nanoTime1, long nanoTime2)
    {
        return nanoTime1 - nanoTime2 <= 0;
    }

    /**
     * Spin waits for the specified number of nanoseconds.
     *
     * @param nanos the amount of nanoseconds to spin wait
     */
    public static void spinWait(long nanos)
    {
        long start = now();
        while (since(start) < nanos)
        {
            Thread.onSpinWait();
        }
    }

    private NanoTime()
    {
    }
}