goroutine通道在for循环中

huangapple go评论82阅读模式
英文:

goroutine channels over a for loop

问题

我的main函数从文件中读取JSON,将其解组为结构体,将其转换为另一种结构体类型,并通过标准输出打印格式化的JSON。

我正在尝试使用goroutine和通道来为我的for循环添加并发性。

func main() {
    muvMap := map[string]string{"male": "M", "female": "F"}
    fileA, err := os.Open("serviceAfileultimate.json")
    if err != nil {
        panic(err)
    }
    defer fileA.Close()

    data := make([]byte, 10000)
    count, err := fileA.Read(data)
    if err != nil {
        panic(err)
    }

    dataBytes := data[:count]

    var servicesA ServiceA
    json.Unmarshal(dataBytes, &servicesA)
    var servicesB = make([]ServiceB, servicesA.Count)
    goChannels := make(chan ServiceB, servicesA.Count)

    for i := 0; i < servicesA.Count; i++ {
        go func() {
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Address").SetString(Merge(&servicesA.Users[i].Location))
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Date_Of_Birth").SetString(dateCopyTransform(servicesA.Users[i].Dob))
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Email").SetString(servicesA.Users[i].Email)
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Fullname").SetString(Merge(&servicesA.Users[i].Name))
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Gender").SetString(muvMap[servicesA.Users[i].Gender])
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Phone").SetString(servicesA.Users[i].Cell)
            reflect.ValueOf(&servicesB[i]).Elem().FieldByName("Username").SetString(servicesA.Users[i].Username)
            goChannels <- servicesB[i]
        }()
    }

    for index := range goChannels {
        json.NewEncoder(os.Stdout).Encode(index)
    }
}

它可以编译,但返回的消息类似于:

goroutine 1 [chan receive]: main.main() C://.....go.94 +0x55b.
英文:

My main function reads json from a file, unmarshals it into a struct, converts it into another struct type and spits out formatted JSON through stdout.

I'm trying to implement goroutines and channels to add concurrency to my for loop.

func main() {
muvMap := map[string]string{&quot;male&quot;: &quot;M&quot;, &quot;female&quot;: &quot;F&quot;}
fileA, err := os.Open(&quot;serviceAfileultimate.json&quot;)
if err != nil {
panic(err)
}
defer fileA.Close()
data := make([]byte, 10000)
count, err := fileA.Read(data)
if err != nil {
panic(err)
}
dataBytes := data[:count]
var servicesA ServiceA
json.Unmarshal(dataBytes, &amp;servicesA)
var servicesB = make([]ServiceB, servicesA.Count)
goChannels := make(chan ServiceB, servicesA.Count)
for i := 0; i &lt; servicesA.Count; i++ {
go func() {
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Address&quot;).SetString(Merge(&amp;servicesA.Users[i].Location))
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Date_Of_Birth&quot;).SetString(dateCopyTransform(servicesA.Users[i].Dob))
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Email&quot;).SetString(servicesA.Users[i].Email)
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Fullname&quot;).SetString(Merge(&amp;servicesA.Users[i].Name))
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Gender&quot;).SetString(muvMap[servicesA.Users[i].Gender])
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Phone&quot;).SetString(servicesA.Users[i].Cell)
reflect.ValueOf(&amp;servicesB[i]).Elem().FieldByName(&quot;Username&quot;).SetString(servicesA.Users[i].Username)
goChannels &lt;- servicesB[i]
}()
}
for index := range goChannels {
json.NewEncoder(os.Stdout).Encode(index)
}
}

It compiles but is returning messages like:

goroutine 1 [chan receive]: main.main() C://.....go.94 +0x55b.

答案1

得分: 1

你正在打印通道的信息,而不是其中包含的数据。你不需要循环,只需要接收然后打印。

json := <-index
json.NewEncoder(os.Stdout).Encode(json)

现在我需要指出的是,这段代码不会阻塞。如果你想一直读取,直到所有工作完成,你需要一些形式的锁定/协调机制。

通常会看到类似以下的代码:

for {
    select {
        case json := <-jsonChannel:
            // 处理数据
        case <-abort:
            // 退出循环
    }
}

处理这种情况。另外,只是提醒一下,你正在使用默认容量初始化通道(意味着它是一个缓冲通道),这相当奇怪。我建议你查阅一些关于这个主题的教程,因为整体上你的设计需要一些改进才能成为非并发实现的改进。最后,你可以找到一些库来为你抽象出一部分工作,大多数人可能会建议你这样做。这里有一个例子:https://github.com/lytics/squaredance

英文:

You're printing the channels info, not the data it contains. You don't want a loop, you just want to receive then print.

   json := &lt;-index
json.NewEncoder(os.Stdout).Encode(json)

Now I do I need to point out, that code is not going to block. If you want to keep reading until all work is done you need some kind of locking/coordination mechanism.

You'll often see things like

for {
select {
case json := &lt;-jsonChannel:
// do stuff
case &lt;-abort:
// get out of here 
}
}

To deal with that. Also, just fyi you're initializing your channel with a default capacity (meaning it's a buffered channel) which is pretty odd. I'd recommend reviewing some tutorials on the topic cause overall your design needs some work actually be an improvement of non-concurrent implementations. Lastly you can find libraries to abstract some of this work for you and most people would probably recommend you do. Here's an example; https://github.com/lytics/squaredance

huangapple
  • 本文由 发表于 2015年6月19日 23:17:03
  • 转载请务必保留本文链接:https://go.coder-hub.com/30941706.html
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