* called multiple times.
   *
   * <p>If {@link #stopAsync} is called on a {@link State#STARTING} service, this method is not
   * invoked immediately. Instead, it will be deferred until after the service is {@link
   * State#RUNNING}. Services that need to cancel startup work can override {@link #doCancelStart}.
   */
  @ForOverride
  protected abstract void doStop();

  /**

  /**
   * Start of Heading: A communication control character used at the beginning of a sequence of
   * characters which constitute a machine-sensible address or routing information. Such a sequence
   * is referred to as the "heading." An STX character has the effect of terminating a heading.
   *
   * @since 8.0
   */
  public static final byte SOH = 1;

  /**

@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public abstract class RateLimiter {
  /**
   * Creates a {@code RateLimiter} with the specified stable throughput, given as "permits per
   * second" (commonly referred to as <i>QPS</i>, queries per second).
   *
   * <p>The returned {@code RateLimiter} ensures that on average no more than {@code
   * permitsPerSecond} are issued during any given second, with sustained requests being smoothly

   * there's no way to assign a {@code @Nullable T} to a field {@code T foo;} and instruct the
   * analysis that that means "plain {@code T}" rather than the inferred type {@code @Nullable T}.
   * (Even if supported added {@code @NonNull}, that would not help, since the problem case
   * addressed by this method is the case in which {@code T} has parametric nullness -- and thus its

          put(closeable, executor);
          return;
        }
      }
      closeQuietly(closeable, executor);
    }

    /**
     * Returns a latch that reaches zero when this objects' deferred closeables have been closed.
     */
    CountDownLatch whenClosedCountDown() {
      if (closed) {
        return new CountDownLatch(0);
      }
      synchronized (this) {
        if (closed) {

   * there's no way to assign a {@code @Nullable T} to a field {@code T foo;} and instruct the
   * analysis that that means "plain {@code T}" rather than the inferred type {@code @Nullable T}.
   * (Even if supported added {@code @NonNull}, that would not help, since the problem case
   * addressed by this method is the case in which {@code T} has parametric nullness -- and thus its

      "You" (or "Your") shall mean an individual or Legal Entity
      exercising permissions granted by this License.

      "Source" form shall mean the preferred form for making modifications,
      including but not limited to software source code, documentation
      source, and configuration files.

      "Object" form shall mean any form resulting from mechanical

   *
   * @since 21.0
   */
  public static <E> Collector<E, ?, ImmutableSet<E>> toImmutableSet() {
    return CollectCollectors.toImmutableSet();
  }

  /**
   * Returns the empty immutable set. Preferred over {@link Collections#emptySet} for code
   * consistency, and because the return type conveys the immutability guarantee.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */

  /**
   * The "base64url" encoding specified by <a
   * href="http://tools.ietf.org/html/rfc4648#section-5">RFC 4648 section 5</a>, Base 64 Encoding
   * with URL and Filename Safe Alphabet, also sometimes referred to as the "web safe Base64." (This
   * is the same as the base 64 encoding with URL and filename safe alphabet from <a
   * href="http://tools.ietf.org/html/rfc3548#section-4">RFC 3548</a>.)
   *

  // http://docs.oracle.com/javase/6/docs/technotes/guides/security/crypto/CryptoSpec.html
  //  - Some providers may choose to also include alias names.
  //  - For example, the "SHA-1" algorithm might be referred to as "SHA1".
  //  - The algorithm name is not case-sensitive.
  private static final ImmutableMap<String, HashFunction> ALGORITHMS =
      new ImmutableMap.Builder<String, HashFunction>()
          .put("MD5", Hashing.md5())