如何使用Socket.select

Question

如何在标准 ML 中使用 Socket.select？

根据 docs，我应该将三个套接字列表和一个超时 option 传递给它，并在任何套接字准备就绪时传递函数 returns做某事（我假设，但不确定输出列表中的套接字仅需要注意的套接字）。然而，

输入似乎既不是元组，也不是四个参数。我该如何构建合适的输入结构？
select 获取 returns 的 sock_desc 列表，似乎没有办法从其 [=14] 中获取 socket =].似乎也没有一种构建有效地图的方法，因为似乎不可能订购两个 sock_descs，只能比较它们是否相等。一旦我从 select 获得了 return 值，我该如何使用 returned 套接字做任何有用的事情，比如写出响应，或者在它们上调用 accept ？

Answer 1

输入参数是一个包含四个字段的记录，因此您的代码应如下所示：

Socket.select {
  rds = readSocketDescs,
  wrs = writeSocketDescs,
  exs = exnSocketDescs,
  timeout = SOME (Time.fromSeconds 10)
}

是的，不确定，可能您需要自己使用列表来保留映射。效率不高，但我看不出你还能做什么。

(**
 * Produces a list of all the pairs in `listPair`, whose keys are present
 * in `whiteList`. Example:
 *
 * ```sml
 * - filterListPair op= [(1,"a"), (2,"b"), (3,"c")] [2,3];
 * val it = [(2,"b"),(3,"c")] : (int * string) list
 * ```
 *)
fun filterListPair eq listPair whiteList =
  let
    fun recur listPair whiteList result =
      case (listPair, whiteList) of
        ([], _) => result
      | (_, []) => result
      | ((x, y) :: xs, k :: ks) =>
          if eq (x, k)
          then recur xs ks ((x, y) :: result)
          else recur xs whiteList result
  in
    List.rev (recur listPair whiteList [])
  end

val sockets = [ (* what have you *) ]
val descsToSockets = List.map (fn s => (Socket.sockDesc s, s)) sockets
val { rds, wrs, exs } = Socket.select {
  rds = readSocketDescs,
  wrs = writeSocketDescs,
  exs = exnSocketDescs,
  timeout = SOME (Time.fromSeconds 10)
}

(*
 * The contract of Socket.select ensures that the order in input lists
 * is preserved in the output lists, so we can use `filterListPair`.
 *)
val selectedReadSockets =
  filterListPair Socket.sameDesc descsToSockets rds

如何使用Socket.select

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