var maxRequests = 64
    get() = this.withLock { field }
    set(maxRequests) {
      require(maxRequests >= 1) { "max < 1: $maxRequests" }
      this.withLock {
        field = maxRequests
      }
      promoteAndExecute()
    }

  /**
   * The maximum number of requests for each host to execute concurrently. This limits requests by
   * the URL's host name. Note that concurrent requests to a single IP address may still exceed this