Golang – 在扇入中进行排序

huangapple
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英文:

Golang - Sorting on fan in

问题

我正在随机生成一堆日志消息，生成后，我需要按时间戳对它们进行排序，然后将它们写入日志。我正在利用sort库的sort.Interface特性，以便根据时间戳进行排序。我正在使用一个并发设计的扇入模式，所以我的排序函数会聚合所有来自goroutine的日志消息，然后对它们进行排序。

以下是我的代码：

  1. type CommonLogFormat struct {
  2.     HostIP         string
  3.     UserIdent      string
  4.     User           string
  5.     Timestamp      string
  6.     Request        string
  7.     HttpStatusCode int
  8.     Size           int
  9. }
  11. type Logs struct {
  12.     Messages []*CommonLogFormat
  13. }
  15. func sortByTimestamp(ch chan<- *CommonLogFormat) *Logs {
  16.     logs := &Logs{Messages: make([]*CommonLogFormat, 0)}
  18.     for i := range ch {
  19.         logs.Messages = append(logs.Messages, i)
  20.     }
  22.     sort.Sort(logs)
  24.     return logs
  25. }
  27. func (l Logs) Len() int {
  28.     return len(l.Messages)
  29. }
  31. func (l Logs) Less(i, j int) bool {
  32.     return l.Messages[i].Timestamp < l.Messages[j].Timestamp
  33. }
  35. func (l *Logs) Swap(i, j int) {
  36.     l.Messages[i], l.Messages[j] = l.Messages[j], l.Messages[i]
  37. }

然而，当我尝试从通道接收日志消息时，我遇到了以下错误：

  1. invalid operation: <-i (receive from non-chan type *CommonLogFormat)

为什么我无法从通道接收值？

英文:

I am randomly generating a bunch of log messages, and after they have been generated, I need to sort them by timestamp before writing them to the logs. I'm utilising the sort.Interface aspect of the sort library so I can sort based on my timestamp. I'm using a fan-in concurrency design, so my sorting function aggregates all the log messages from the goroutines, then sorts them.

Here is my code:

  1. type CommonLogFormat struct {
  2. 	HostIP         string
  3. 	UserIdent      string
  4. 	User           string
  5. 	Timestamp      string
  6. 	Request        string
  7. 	HttpStatusCode int
  8. 	Size           int
  9. }
  11. type Logs struct {
  12. 	Messages []*CommonLogFormat
  13. }
  15. func sortByTimestamp(ch chan &lt;- *CommonLogFormat) *Logs {
  16. 	logs := &amp;Logs{Messages: make([]*CommonLogFormat, 1)}
  18. 	for i := range ch {
  19. 		logs.Messages = append(logs.Messages, &lt;- i)
  20. 	}
  22. 	sort.Sort(logs)
  24. 	return logs
  25. }
  27. func (l Logs) Len() int {
  28. 	return len(l.Messages)
  29. }
  31. func (l Logs) Less(i,j int) bool {
  32. 	return l.Messages[i].Timestamp &lt; l.Messages[j].Timestamp
  33. }
  35. func (l *Logs) Swap(i,j int) {
  36. 	l.Messages[i], l.Messages[j] = l.Messages[j], l.Messages[i]
  37. }

However, when I go to receive a log message from the channel, I get this error:

  1. invalid operation: &lt;-i (receive from non-chan type *CommonLogFormat)

Why can't I receive a value from the channel?

答案1

得分: 2

我认为错误信息已经很明显了。看看这段代码：

  1. for i := range ch {
  2.     logs.Messages = append(logs.Messages, <-i)
  3. }

ch 的类型是 chan<- *CommonLogFormat，也就是一个通道。for range 循环遍历通道，将通道中发送的值存储在循环变量 i 中。i 不是一个通道，而是通道中发送的值，所以它的类型是 *CommonLogFormat。

所以没有必要，也不能从中接收，因为它已经是你想要接收的值了。只需简单地将 i 追加到 logs.Messages 中：

  1. for i := range ch {
  2.     logs.Messages = append(logs.Messages, i)
  3. }

在 规范：For 语句 中详细说明了在 for range 的情况下循环变量的含义：

  1. Range 表达式                          第一个值          第二个值
  3. 数组或切片  a  [n]E, *[n]E, or []E    索引    i  int    a[i]       E
  4. 字符串          s  string 类型            索引    i  int    参见下文  rune
  5. 映射             m  map[K]V                键      k  K      m[k]       V
  6. 通道         c  chan E, <-chan E       元素  e  E
  8. 最后一行适用于遍历通道的情况，第一个迭代值是元素。
  10. > 对于通道，产生的迭代值是在通道上发送的连续值，直到通道被关闭为止。如果通道为 `nil`，则 range 表达式将永远阻塞。
  12.   [1]: https://golang.org/ref/spec#For_statements
  13.   [2]: https://golang.org/ref/spec#Close
英文:

I think the error message is pretty self-explanatory. Look at this:

  1. for i := range ch {
  2.     logs.Messages = append(logs.Messages, &lt;- i)
  3. }

ch is of type chan &lt;- *CommonLogFormat. ch is a channel. The for range loop over the channel yields the values sent on the channel, which will be stored in the loop variable i. i is not a channel, but the values sent on the channel, so it will be of type *CommonLogFormat.

So no need, and you actually can't receive from it, it is already what you would want to receive from it. Simply append i:

  1. for i := range ch {
  2.     logs.Messages = append(logs.Messages, i)
  3. }

The Spec: For statements details what the loop variables are in case of for range:

  1. Range expression                          1st value          2nd value
  3. array or slice  a  [n]E, *[n]E, or []E    index    i  int    a[i]       E
  4. string          s  string type            index    i  int    see below  rune
  5. map             m  map[K]V                key      k  K      m[k]       V
  6. channel         c  chan E, &lt;-chan E       element  e  E

The last line applies in case of ranging over a channel, and the first iteration value is the element.

> For channels, the iteration values produced are the successive values sent on the channel until the channel is closed. If the channel is nil, the range expression blocks forever.

huangapple
  • 本文由 发表于 2016年12月5日 04:05:18
  • 转载请务必保留本文链接：https://go.coder-hub.com/40963042.html
  • channel
  • concurrency
  • for-loop
  • go
  • sorting
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