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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc;
import com.google.inject.ImplementedBy;
import com.yahoo.jdisc.core.SystemTimer;
import java.time.Clock;
import java.time.Instant;
import java.time.ZoneId;
import java.time.ZoneOffset;
/**
* <p>This class provides access to the current time in milliseconds, as viewed by the {@link Container}. Inject an
* instance of this class into any component that needs to access time, instead of using
* <code>System.currentTimeMillis()</code>.</p>
*
* @author Simon Thoresen Hult
*/
@ImplementedBy(SystemTimer.class)
public interface Timer {
/**
* <p>Returns the current time in milliseconds. Note that while the unit of time of the return value is a
* millisecond, the granularity of the value depends on the underlying operating system and may be larger. For
* example, many operating systems measure time in units of tens of milliseconds.</p>
*
* <p> See the description of the class <code>Date</code> for a discussion of slight discrepancies that may arise
* between "computer time" and coordinated universal time (UTC).</p>
*
* @return The difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
* @see java.util.Date
*/
long currentTimeMillis();
/** Convenience method for getting an java.util.Instance from currentTimeMillis(). */
default Instant currentTime() {
return Instant.ofEpochMilli(currentTimeMillis());
}
/** Return a UTC Clock backed by this timer. */
default Clock toUtcClock() {
return new ClockAdapter(this, ZoneOffset.UTC);
}
/** Create a Timer backed by the given Clock. */
static Timer fromClock(Clock clock) {
return clock::millis;
}
class ClockAdapter extends Clock {
private final Timer timer;
private final ZoneId zoneId;
private ClockAdapter(Timer timer, ZoneId zoneId) {
this.timer = timer;
this.zoneId = zoneId;
}
@Override public ZoneId getZone() { return zoneId; }
@Override public Clock withZone(ZoneId zone) { return new ClockAdapter(timer, zoneId); }
@Override public Instant instant() { return timer.currentTime(); }
}
}
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