We have 3 different things that we synchronize on.

#### Http2Connection

This lock guards internal state of each connection. This lock is never held for blocking operations. That means that we acquire the lock, read or write a few fields and release the lock. No I/O and no application-layer callbacks.

#### Http2Stream

import org.junit.jupiter.api.extension.RegisterExtension

class PlatformTest {
  @RegisterExtension
  var platform = PlatformRule()

  @Test
  fun alwaysBuilds() {
    Platform()
  }

  /** Guard against the default value changing by accident.  */
  @Test
  fun defaultPrefix() {
    assertThat(Platform().getPrefix()).isEqualTo("OkHttp")
  }

  @Test
  fun testToStringIsClassname() {