* operations.
 *
 * <p>Certain cache configurations will result in the accrual of periodic maintenance tasks which
 * will be performed during write operations, or during occasional read operations in the absence of
 * writes. The {@link Cache#cleanUp} method of the returned cache will also perform maintenance, but
 * calling it should not be necessary with a high throughput cache. Only caches built with {@link

   * multimap to be a view, but it means that the function will be applied many times for bulk
   * operations like {@link Multimap#containsValue} and {@code Multimap.toString()}. For this to
   * perform well, {@code function} should be fast. To avoid lazy evaluation when the returned
   * multimap doesn't need to be a view, copy the returned multimap into a new multimap of your
   * choosing.
   *
   * @since 7.0

   * multimap to be a view, but it means that the function will be applied many times for bulk
   * operations like {@link Multimap#containsValue} and {@code Multimap.toString()}. For this to
   * perform well, {@code function} should be fast. To avoid lazy evaluation when the returned
   * multimap doesn't need to be a view, copy the returned multimap into a new multimap of your
   * choosing.
   *
   * @since 7.0

     */
    fun retryOnConnectionFailure(retryOnConnectionFailure: Boolean) =
      apply {
        this.retryOnConnectionFailure = retryOnConnectionFailure
      }

    /**
     * Configure this client to perform fast fallbacks by attempting multiple connections
     * concurrently, returning once any connection connects successfully.
     *
     * This implements Happy Eyeballs ([RFC 6555][rfc_6555]), balancing connect latency vs.

_2018-07-12_

 *  **OkHttp's new okhttp-tls submodule tames HTTPS and TLS.**

    `HeldCertificate` is a TLS certificate and its private key. Generate a certificate with its
    builder then use it to sign another certificate or perform a TLS handshake. The
    `certificatePem()` method encodes the certificate in the familiar PEM format
    (`--- BEGIN CERTIFICATE ---`); the `privateKeyPkcs8Pem()` does likewise for the private key.

    assertThat(response3.body.string()).isEqualTo("def")
    assertThat(server.takeRequest().exchangeIndex).isEqualTo(1) // New connection.
  }

  /**
   * We had a bug where we'd perform infinite retries of route that fail with connection shutdown
   * errors. The problem was that the logic that decided whether to reuse a route didn't track
   * certain HTTP/2 errors. https://github.com/square/okhttp/issues/5547

## Changes since v1.3.0-beta.1

### Experimental Features

  // 'inputFuture' field is read and where we will have to consider visibility of the write
  // operation in the constructor.
  //
  // 1. In the listener that performs the callback. In this case it is fine since inputFuture is
  //    assigned prior to calling addListener, and addListener happens-before any invocation of the

      }
      V value = entry.getValue();
      if (value == null) {
        tryDrainReferenceQueues();
        return null;
      }

      return value;
    }

    /**
     * Performs routine cleanup following a read. Normally cleanup happens during writes, or from
     * the cleanupExecutor. If cleanup is not observed after a sufficient number of reads, try
     * cleaning up from the read thread.
     */

    checkNotNull(iterators, "iterators");
    checkNotNull(comparator, "comparator");

    return new MergingIterator<>(iterators, comparator);
  }

  /**
   * An iterator that performs a lazy N-way merge, calculating the next value each time the iterator
   * is polled. This amortizes the sorting cost over the iteration and requires less memory than
   * sorting all elements at once.
   *