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();

    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

    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>

        "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>