if (existing != null) {
        return existing;
      }
      L created = supplier.get();
      ArrayReference<L> newRef = new ArrayReference<>(created, index, queue);
      while (!locks.compareAndSet(index, existingRef, newRef)) {
        // we raced, we need to re-read and try again
        existingRef = locks.get(index);
        existing = existingRef == null ? null : existingRef.get();

  }

  /**
   * Simulate some of the races that can happen on add. We can't easily simulate the race that
   * happens when an {@link AtomicInteger#compareAndSet} fails, but we can simulate the case where
   * the putIfAbsent returns a non-null value, and the case where the replace() of an observed zero
   * fails.
   */
  public void testAdd_withFailures() {

      return domainLabels.dropLast(1)
    }

    return domainLabels
  }

  private fun findMatchingRule(domainLabels: List<String>): List<String> {
    if (!listRead.get() && listRead.compareAndSet(false, true)) {
      readTheListUninterruptibly()
    } else {
      try {
        readCompleteLatch.await()
      } catch (_: InterruptedException) {

    val newConnectionsNeeded: Int

    while (true) {
      val oldMap = this.addressStates
      val newMap = oldMap + (address to state)
      if (addressStatesUpdater.compareAndSet(this, oldMap, newMap)) {
        val oldPolicyMinimumConcurrentCalls = oldMap[address]?.policy?.minimumConcurrentCalls ?: 0
        newConnectionsNeeded = policy.minimumConcurrentCalls - oldPolicyMinimumConcurrentCalls

   * test case failure. Only the first failure is recorded; subsequent calls to this method from
   * within the same test have no effect.
   */
  public void threadRecordFailure(Throwable t) {
    threadFailure.compareAndSet(null, t);
  }

  @Override
  public void setUp() {
    setDelays();
  }

  /**
   * Extra checks that get done for all test cases.
   *

   * test case failure. Only the first failure is recorded; subsequent calls to this method from
   * within the same test have no effect.
   */
  public void threadRecordFailure(Throwable t) {
    threadFailure.compareAndSet(null, t);
  }

  @Override
  public void setUp() {
    setDelays();
  }

  /**
   * Extra checks that get done for all test cases.
   *

    val ifNoneMatch = AtomicReference<String?>()
    client =
      client.newBuilder()
        .addNetworkInterceptor(
          Interceptor { chain: Interceptor.Chain ->
            ifNoneMatch.compareAndSet(null, chain.request().header("If-None-Match"))
            chain.proceed(chain.request())
          },
        )
        .build()

    // Confirm the value is cached and intercepted.

        "Expected state to be %s, but it was %s",
        oldState,
        newState);
  }

  private boolean compareAndUpdateState(State oldState, State newState) {
    return state.compareAndSet(oldState, newState);
  }

  // TODO(dpb): Should we use a pair of ArrayLists instead of an IdentityHashMap?
  private static final class CloseableList extends IdentityHashMap<AutoCloseable, Executor>