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package fish.payara.microprofile.metrics.impl;

import java.lang.management.ManagementFactory;

/**
 * An abstraction for how time passes. It is passed to {@link Timer} to track
 * timing.
 */
@FunctionalInterface
public interface Clock {

    /**
     * Returns the current time tick.
     *
     * @return time tick in nanoseconds
     */
    long getTick();

    /**
     * Returns the current time in milliseconds.
     *
     * @return time in milliseconds
     */
    default long getTime() {
        return System.currentTimeMillis();
    }

    /**
     * A clock implementation which returns the current time in epoch
     * nanoseconds.
     */
    Clock DEFAULT = () -> System.nanoTime();

    /**
     * The default clock to use.
     *
     * @return the {@link #DEFAULT} {@link Clock} instance
     */
    public static Clock defaultClock() {
        return DEFAULT;
    }

    /**
     * A clock implementation which returns the current thread's CPU time.
     */
    Clock THREAD_CPU_TIME = () -> ManagementFactory.getThreadMXBean().getCurrentThreadCpuTime();
}