if (pos == limit) return false // Malformed.
        val c = string[pos++]
        val digit =
          when (c) {
            in 'a'..'z' -> c - 'a'
            in 'A'..'Z' -> c - 'A'
            in '0'..'9' -> c - '0' + 26
            else -> return false // Malformed.
          }
        val deltaI = digit * w
        if (i > Int.MAX_VALUE - deltaI) return false // Prevent overflow.
        i += deltaI

      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
   * limit: multiple hostnames may share an IP address or be routed through the same HTTP proxy.
   *