发送通道后 Goroutine 不执行

Question

package main

import (
    "fmt"
    "sync"
)

// PUT function
func put(hashMap map[string](chan int), key string, value int, wg *sync.WaitGroup) {
    defer wg.Done()
    fmt.Printf("this is getting printed")
    hashMap[key] <- value
    fmt.Printf("this is not getting printed")
    fmt.Printf("PUT sent %d\n", value)
}

func main() {
    var value int
    var key string
    wg := &sync.WaitGroup{}
    hashMap := make(map[string](chan int), 100)
    key = "xyz"
    value = 100
    for i := 0; i < 5; i++ {
        wg.Add(1)
        go put(hashMap, key, value, wg)
    }
    wg.Wait()
}

put 函数中的最后两个打印语句未打印出来，我正在尝试根据键将值放入映射中。

以及在这种情况下如何关闭 hashMap。

Answer 1

您需要创建一个频道，例如hashMap[key] = make(chan int)
由于您不是从频道读取数据，因此您需要缓冲频道才能使其正常工作：

    key := "xyz"
    hashMap[key] = make(chan int, 5)

试试下面的代码：

func put(hashMap map[string](chan int), key string, value int, wg *sync.WaitGroup) {
    hashMap[key] <- value
    fmt.Printf("PUT sent %d\n", value)
    wg.Done()
}
func main() {
    var wg sync.WaitGroup
    hashMap := map[string]chan int{}
    key := "xyz"
    hashMap[key] = make(chan int, 5)
    for i := 0; i < 5; i++ {
        wg.Add(1)
        go put(hashMap, key, 100, &wg)
    }
    wg.Wait()
}

输出：

PUT sent 100
PUT sent 100
PUT sent 100
PUT sent 100
PUT sent 100

Answer 2

此外，您的代码可以简化为这样。为什么不必要地传递参数！一个额外的修改是我取不同的值让你更清楚地理解这个概念。

package main

import (
    "log"
    "sync"
)

func put(hash chan int, wg *sync.WaitGroup) {
    defer wg.Done()
    log.Println("Put sent: ", <-hash)
}

func main() {
    hashMap := map[string]chan int{}
    key := "xyz"
    var wg sync.WaitGroup
    hashMap[key] = make(chan int, 5)
    for i := 0; i < 5; i++ {
        value := i
        wg.Add(1)
        go func(val int) {
            hashMap[key] <- val
            put(hashMap[key], &wg)
        }(value)
    }
    wg.Wait()
}

Answer 3

我解决问题的方法是：

// PUT function
func put(hashMap map[string](chan int), key string, value int, wg *sync.WaitGroup) {
    defer wg.Done()
    fmt.Printf("this is getting printed")
    hashMap[key] <- value // <-- nil problem
    fmt.Printf("this is not getting printed")
    fmt.Printf("PUT sent %d\n", value)
}

在 put 函数中的这一行代码 hashMap[key] <- value 中，它不能接受 value 因为 chan int 是 nil 定义在 put (hashMap map[string](chan int) 参数.

// PUT function
func put(hashMap map[string](chan int), cval chan int, key string, value int, wg *sync.WaitGroup) {
    defer wg.Done()
    fmt.Println("this is getting printed")
    cval <- value // put the value in chan int (cval) which is initialized
    hashMap[key] = cval // set the cval(chan int) to hashMap with key
    fmt.Println("this is not getting printed")
    fmt.Printf("PUT sent %s %d\n", key, value)
}

func main() {
    var value int
    wg := &sync.WaitGroup{}

    cval := make(chan int,100)
    hashMap := make(map[string](chan int), 100)

    value = 100
    for i := 0; i < 5; i++ {
        wg.Add(1)
        go put(hashMap, cval, fmt.Sprintf("key%d",i), value, wg)
    }
    wg.Wait()

    /* uncomment to test cval 
    close(cval)

    fmt.Println("Result:",<-hashMap["key2"])
    fmt.Println("Result:",<-hashMap["key1"])
    cval <- 88 // cannot send value to a close channel
    hashMap["key34"] = cval
    fmt.Println("Result:",<-hashMap["key1"])
    */


}

在我的代码示例中。我将 cval 缓冲通道 100 相同大小初始化为 hashMap 并将 cval 作为 put 函数中的值传递。您只能关闭 cval 而不能关闭 hashMap 本身。

发送通道后 Goroutine 不执行

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goroutine