* see calls in Google code that pass a null `dir` to a FilenameFilter.... So let's declare the
   * parameter as non-nullable (since passing null to a FilenameFilter is unsafe in general), but if
   * someone still manages to pass null, let's continue to have the method work.
   *
   * (PatternFilenameFilter is of course one of those classes that shouldn't be a publicly visible

  @J2ktIncompatible // serialization
  @GwtIncompatible // serialization
  Object writeReplace() {
    return super.writeReplace();
  }

  // No longer used for new writes, but kept so that old data can still be read.
  @GwtIncompatible // serialization
  @J2ktIncompatible
  @SuppressWarnings("unused")
  private static class SerializedForm<V> implements Serializable {
    final ImmutableMap<?, V> map;

     * filesystem) does our prod code look up the username. Thus, this test doesn't necessarily test
     * anything interesting under most environments. Still, we can run it (except for Android, at
     * least old versions), so we mostly do. This is useful because we don't actually run our CI on
     * Windows under Java 8, at least as of this writing.
     *

            java: 21
            root-pom: pom.xml
    runs-on: ${{ matrix.os }}
    env:
      ROOT_POM: ${{ matrix.root-pom }}
    steps:
      # Cancel any previous runs for the same branch that are still running.
      - name: 'Cancel previous runs'
        uses: styfle/cancel-workflow-action@85880fa0301c86cca9da44039ee3bb12d3bedbfa # 0.12.1
        with:
          access_token: ${{ github.token }}

   * buildOrThrow(), or vice versa. So in particular, if we modify alternatingKeysAndValues to
   * eliminate duplicate keys (for buildKeepingLast()) then we have to ensure that a later call to
   * buildOrThrow() will still throw as if the duplicates had not been eliminated. And the exception
   * message must mention two values that were associated with the duplicate key in two different

          .put("MD5", Hashing.md5())
          .put("SHA", Hashing.sha1()) // Not the official name, but still works
          .put("SHA1", Hashing.sha1()) // Not the official name, but still works
          .put("sHa-1", Hashing.sha1()) // Not the official name, but still works
          .put("SHA-1", Hashing.sha1())
          .put("SHA-256", Hashing.sha256())
          .put("SHA-384", Hashing.sha384())

  // TODO: Test blocking to re-enter monitor after being signaled.
  // TODO: Test interrupts with both interruptible and uninterruptible monitor.
  // TODO: Test multiple waiters: If guard is still satisfied, signal next waiter.
  // TODO: Test multiple waiters: If guard is no longer satisfied, do not signal next waiter.

    ticker.advance(ttl * 2 / 3, MILLISECONDS);

    assertEquals(10, CacheTesting.expirationQueueSize(cache));
    assertEquals(10, removalListener.getCount());

    // check that new values are still there - they still have 10 ms to live
    for (int i = 0; i < 10; i++) {
      loader.reset();
      assertEquals(Integer.valueOf(i + shift2), cache.getUnchecked(keyPrefix + i));

    assertEquals(
        "next() should still return first element after peeking", "A", peekingIterator.next());

    assertEquals("Should be able to peek() at middle element", "B", peekingIterator.peek());
    assertEquals(
        "Should be able to peek() middle element multiple times", "B", peekingIterator.peek());
    assertEquals(
        "next() should still return middle element after peeking", "B", peekingIterator.next());

  /**
   * Returns a {@link ScheduledExecutorService} that never executes anything.
   *
   * <p>The {@code shutdownNow} method of the returned executor always returns an empty list despite
   * the fact that everything is still technically awaiting execution. The {@code getDelay} method
   * of any {@link ScheduledFuture} returned by the executor will always return the max long value
   * instead of the time until the user-specified delay.
   */