Cancellation if implemented sensibly in both directions.
Cancelling a coroutine scope, will cancel the call.
Cancelling a call, will throw a CancellationException

 * This is typical for Java but atypical for HTTP/2. This is motivated by exception transparency:
 * an [IOException] that was triggered by a certain caller can be caught and handled by that caller.
 */
@Suppress("NAME_SHADOWING")
class Http2Connection internal constructor(builder: Builder) : Closeable {
  internal val lock: ReentrantLock = ReentrantLock()