*
   * If more than [maxRequestsPerHost] requests are in flight when this is invoked, those requests
   * will remain in flight.
   *
   * WebSocket connections to hosts **do not** count against this limit.
   */
  var maxRequestsPerHost = 5
    get() = this.withLock { field }
    set(maxRequestsPerHost) {
      require(maxRequestsPerHost >= 1) { "max < 1: $maxRequestsPerHost" }
      this.withLock {