org.eclipse.jgit/src/org/eclipse/jgit/util/time/MonotonicSystemClock.java

/*
 * Copyright (C) 2016, Google Inc.
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
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package org.eclipse.jgit.util.time;

import static java.util.concurrent.TimeUnit.MICROSECONDS;
import static java.util.concurrent.TimeUnit.MILLISECONDS;

import java.time.Duration;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

/**
 * A {@link org.eclipse.jgit.util.time.MonotonicClock} based on
 * {@code System.currentTimeMillis}.
 *
 * @since 4.6
 */
public class MonotonicSystemClock implements MonotonicClock {
	private static final AtomicLong before = new AtomicLong();

	private static long nowMicros() {
		long now = MILLISECONDS.toMicros(System.currentTimeMillis());
		for (;;) {
			long o = before.get();
			long n = Math.max(o + 1, now);
			if (before.compareAndSet(o, n)) {
				return n;
			}
		}
	}

	/** {@inheritDoc} */
	@Override
	public ProposedTimestamp propose() {
		final long u = nowMicros();
		return new ProposedTimestamp() {
			@Override
			public long read(TimeUnit unit) {
				return unit.convert(u, MICROSECONDS);
			}

			@Override
			public void blockUntil(Duration maxWait) {
				// Assume system clock never goes backwards.
			}
		};
	}
}