frameHeader(
        streamId = 0,
        length = settings.size() * 6,
        type = TYPE_SETTINGS,
        flags = FLAG_NONE,
      )
      for (i in 0 until Settings.COUNT) {
        if (!settings.isSet(i)) continue
        val id =
          when (i) {
            4 -> 3 // SETTINGS_MAX_CONCURRENT_STREAMS renumbered.
            7 -> 4 // SETTINGS_INITIAL_WINDOW_SIZE renumbered.

   *
   * 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 {

    address. Use this to proactively open HTTP connections.

    Connections opened to fulfill this policy are subject to the connection pool's
    `keepAliveDuration` but do not count against the pool-wide `maxIdleConnections` limit.

    This feature increases the client's traffic and the load on the server. Talking to your server's
    operators before adopting it.

    require(keepAliveDuration > 0L) { "keepAliveDuration <= 0: $keepAliveDuration" }
  }

  fun idleConnectionCount(): Int {
    return connections.count {
      it.withLock { it.calls.isEmpty() }
    }
  }

  fun connectionCount(): Int {
    return connections.size
  }

  /**

    assertThat(data2.type).isEqualTo(Http2.TYPE_DATA)
    assertThat(data2.streamId).isEqualTo(3)
    assertArrayEquals("fghi".toByteArray(), data2.data)
  }

  /**
   * Confirm that we account for discarded data frames. It's possible that data frames are in-flight
   * just prior to us canceling a stream.
   */
  @Test fun discardedDataFramesAreCounted() {
    // Write the mocking script.

    redQueue.execute("task") {
      log += "run@${taskFaker.nanoTime}"
    }

    val idleLatch = redQueue.idleLatch()
    assertThat(idleLatch.count).isEqualTo(1)

    taskFaker.advanceUntil(0.µs)
    assertThat(log).containsExactly("run@0")

    assertThat(idleLatch.count).isEqualTo(0)
  }

  @Test fun multipleCallsToIdleLatchReturnSameInstance() {
    redQueue.execute("task") {