*
 * The main implementations will typically be implemented using specific DNS libraries such as
 *  * Android DnsResolver
 *  * OkHttp DnsOverHttps
 *  * dnsjava Resolver
 *
 * Implementations of this interface must be safe for concurrent use.
 */
@ExperimentalOkHttpApi
interface AsyncDns {
  /**
   * Query DNS records for `hostname`, in the order they are received.
   */
  fun query(
    hostname: String,
    callback: Callback,

      canRemove = true;
      /*
       * requireNonNull is safe because occurrencesLeft starts at 0, forcing us to initialize
       * currentEntry above. After that, we never clear it.
       */
      return requireNonNull(currentEntry).getKey();
    }

    @Override
    public void remove() {
      checkRemove(canRemove);
      /*
       * requireNonNull is safe because canRemove is set to true only after we initialize

      if (!compareAndSet(currentThread, DONE)) {
        waitForInterrupt(currentThread);
      }
      if (run) {
        if (error == null) {
          // The cast is safe because of the `run` and `error` checks.
          afterRanInterruptiblySuccess(uncheckedCastNullableTToT(result));
        } else {
          afterRanInterruptiblyFailure(error);
        }
      }
    }
  }

    }

    void calculateNextPermutation() {
      int j = findNextJ();
      if (j == -1) {
        nextPermutation = null;
        return;
      }
      /*
       * requireNonNull is safe because we don't clear nextPermutation until we're done calling this
       * method.
       */
      requireNonNull(nextPermutation);

      int l = findNextL(j);
      Collections.swap(nextPermutation, j, l);

import okio.Buffer
import okio.BufferedSink
import okio.ByteString

/**
 * An [RFC 6455][rfc_6455]-compatible WebSocket frame writer.
 *
 * This class is not thread safe.
 *
 * [rfc_6455]: http://tools.ietf.org/html/rfc6455
 */
class WebSocketWriter(
  private val isClient: Boolean,
  val sink: BufferedSink,
  val random: Random,
  private val perMessageDeflate: Boolean,

        // there are bugs in various JVM that have problems doing this across
        // different filesystem. So we'll incur the small hit to actually copy
        // here and be safe. jvz.
        // ----------------------------------------------------------------------------

        try {
            Files.createDirectories(destination.toPath().getParent());

  }

  /**
   * Returns the empty multimap.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  // Casting is safe because the multimap will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableSetMultimap<K, V> of() {
    return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
  }

   * Collections#emptyList}, and is preferable mainly for consistency and maintainability of your
   * code.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  // Casting to any type is safe because the list will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <E> ImmutableList<E> of() {
    return (ImmutableList<E>) EMPTY;
  }

  /**

	// Make it run twice.
	timer := time.NewTimer(testDrwMutexRefreshInterval * 2)

	select {
	case <-ctx.Done():
		t.Fatal("Lock context canceled which is not expected")
	case <-timer.C:
	}

	// Should be safe operation in all cases
	dm.Unlock(context.Background())
}

// Test canceling context while quorum servers report lock not found
func TestFailedRefreshLock(t *testing.T) {
	if testing.Short() {

        /*
         * requireNonNull is safe because the callers promise to put non-null objects in the first
         * `length` array elements.
         */
        @SuppressWarnings("unchecked") // our callers put only E instances into the array
        E onlyElement = (E) requireNonNull(elements[0]);
        return of(onlyElement);
      default:
        /*