### Locks

We have 3 different things that we synchronize on.

#### Http2Connection

 * that every {@code Runnable} that is {@linkplain #add added} will be executed after {@link
 * #execute()} is called. Any {@code Runnable} added after the call to {@code execute} is still
 * guaranteed to execute. There is no guarantee, however, that listeners will be executed in the
 * order that they are added.
 *

    if (obj instanceof Subscriber) {
      Subscriber that = (Subscriber) obj;
      // Use == so that different equal instances will still receive events.
      // We only guard against the case that the same object is registered
      // multiple times
      return target == that.target && method.equals(that.method);
    }
    return false;
  }

  /**

   * nullness checker can already "prove" are non-null. That means that the first parameter to
   * checkNotNull *should* be annotated to require it to be non-null.
   *
   * However, for a variety of reasons, Google developers have written a ton of code over the past
   * decade that assumes that they can use checkNotNull for non-precondition checks. I had hoped to

      throw e.getCause();
    }
  }

  /**
   * Verify that the listener completes in a reasonable amount of time, and Asserts that the future
   * throws an {@code ExecutableException} and that the cause of the {@code ExecutableException} is
   * {@code expectedCause}.
   */
  public void assertException(Throwable expectedCause) throws Exception {
    // Verify that the listener executed in a reasonable amount of time.

    // If add is supported, verify that IMMUTABLE is not reported.
    assertFalse(collection.spliterator().hasCharacteristics(Spliterator.IMMUTABLE));
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testSpliteratorNotImmutable_collectionAllowsRemove() {
    // If remove is supported, verify that IMMUTABLE is not reported.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common
      control with that entity. For the purposes of this definition,
      "control" means (i) the power, direct or indirect, to cause the

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common
      control with that entity. For the purposes of this definition,
      "control" means (i) the power, direct or indirect, to cause the

    .sslSocketFactory(clientCertificates.sslSocketFactory(), clientCertificates.trustManager())
    .build();
```

With a server that holds a certificate and a client that trusts it we have enough for an HTTPS
handshake. The best part of this example is that we don't need to make our test code insecure with a
a fake `HostnameVerifier` or `X509TrustManager`.

Certificate Authorities
-----------------------

   * values by applying the remapping function. The remapping function accepts the map's existing
   * value for that part of the range and the given value. It returns the value to be associated
   * with that part of the map, or it returns {@code null} to clear that part of the map.
   *
   * <p>Any parts of the range not already present in this map are mapped to the specified value,