MonotonicSystemClock.java

/*
 * Copyright (C) 2016, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

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.
            }
        };
    }
}