*/
@GwtCompatible
public abstract class Ticker {
  /** Constructor for use by subclasses. */
  protected Ticker() {}

  /** Returns the number of nanoseconds elapsed since this ticker's fixed point of reference. */
  public abstract long read();

  /**
   * A ticker that reads the current time using {@link System#nanoTime}.
   *
   * @since 10.0
   */
  public static Ticker systemTicker() {
    return SYSTEM_TICKER;
  }

import com.google.common.base.Ticker;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.time.Duration;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import org.jspecify.annotations.NullMarked;

/**
 * A Ticker whose value can be advanced programmatically in test.
 *

   *
   * @since 15.0
   */
  public static Stopwatch createStarted(Ticker ticker) {
    return new Stopwatch(ticker).start();
  }

  Stopwatch() {
    this.ticker = Ticker.systemTicker();
  }

  Stopwatch(Ticker ticker) {
    this.ticker = checkNotNull(ticker, "ticker");
  }

  /**

            .expireAfterWrite(EXPIRING_TIME, MILLISECONDS)
            .removalListener(removalListener)
            .ticker(ticker)
            .build(loader);
    checkExpiration(cache, loader, ticker, removalListener);
  }

  public void testExpiration_expireAfterAccess() {
    FakeTicker ticker = new FakeTicker();
    CountingRemovalListener<String, Integer> removalListener = countingRemovalListener();

  public void testAdvance() {
    FakeTicker ticker = new FakeTicker();
    assertEquals(0, ticker.read());
    assertThat(ticker.advance(10)).isSameInstanceAs(ticker);
    assertEquals(10, ticker.read());
    ticker.advance(1, MILLISECONDS);
    assertEquals(1000010L, ticker.read());
    ticker.advance(Duration.ofMillis(1));
    assertEquals(2000010L, ticker.read());
  }

   *
   * @since 15.0
   */
  public static Stopwatch createStarted(Ticker ticker) {
    return new Stopwatch(ticker).start();
  }

  Stopwatch() {
    this.ticker = Ticker.systemTicker();
  }

  Stopwatch(Ticker ticker) {
    this.ticker = checkNotNull(ticker, "ticker");
  }

  /**

    ticker.advance(1);
    segment.recordRead(entry, ticker.read());
    segment.expireEntries(ticker.read());
    assertThat(map.containsKey(key)).isTrue();
    assertThat(segment.accessQueue.peek()).isSameInstanceAs(entry);
    assertThat(segment.accessQueue).hasSize(1);

    ticker.advance(1);
    segment.recordRead(entry, ticker.read());
    segment.expireEntries(ticker.read());

    ticker.advance(1);
    segment.recordRead(entry, ticker.read());
    segment.expireEntries(ticker.read());
    assertThat(map.containsKey(key)).isTrue();
    assertThat(segment.accessQueue.peek()).isSameInstanceAs(entry);
    assertThat(segment.accessQueue).hasSize(1);

    ticker.advance(1);
    segment.recordRead(entry, ticker.read());
    segment.expireEntries(ticker.read());

    assertThat(cache.apply(7)).isEqualTo(6);
  }

  @Test
  public void expireAfterAccess() {
    Cache<Integer, Integer> cache =
        CacheBuilder.newBuilder().expireAfterAccess(1000, MILLISECONDS).ticker(fakeTicker).build();

    cache.put(0, 10);
    cache.put(2, 30);

    fakeTicker.advance(999, MILLISECONDS);
    assertThat(cache.getIfPresent(2)).isEqualTo(30);
    fakeTicker.advance(1, MILLISECONDS);

    assertThat(cache.apply(7)).isEqualTo(6);
  }

  @Test
  public void expireAfterAccess() {
    Cache<Integer, Integer> cache =
        CacheBuilder.newBuilder().expireAfterAccess(1000, MILLISECONDS).ticker(fakeTicker).build();

    cache.put(0, 10);
    cache.put(2, 30);

    fakeTicker.advance(999, MILLISECONDS);
    assertThat(cache.getIfPresent(2)).isEqualTo(30);
    fakeTicker.advance(1, MILLISECONDS);