internal fun sendDegradedPingLater() {
    this.withLock {
      if (degradedPongsReceived < degradedPingsSent) return // Already awaiting a degraded pong.
      degradedPingsSent++
      degradedPongDeadlineNs = System.nanoTime() + DEGRADED_PONG_TIMEOUT_NS
    }
    writerQueue.execute("$connectionName ping") {
      writePing(false, DEGRADED_PING, 0)
    }
  }

  class Builder(