Problems when using channels to pass data from one goroutine to another

In concurrent programming in the Go language, using channels is a common way to transfer data between different goroutines. However, some problems may arise when passing data from one goroutine to another. PHP editor Apple will introduce these problems and provide solutions in this article to help you better understand and cope with the difficulties you may encounter when using channels in concurrent programming.

Question content

I have been able to develop the following code, which is supposed to pass data from one routine to another using go channels:

package main

import (
    "fmt"
    "sync"
)

func generateNumbers(total int, wg *sync.WaitGroup) {
    defer wg.Done()
    ch :=make(chan int)

    sum :=0
    for idx := 1; idx <= total; idx++ {
        fmt.Printf("Generating number %d\n", idx)
        sum =sum+idx
        ch <- sum
    }
}

func printNumbers(wg *sync.WaitGroup, ch chan  int) {
    defer wg.Done()

    fmt.Printf("Sum is now",ch)
    for idx := 1; idx <= 3; idx++ {
        fmt.Printf("Printing number %d\n", idx)
    }
}

func main() {
    var wg sync.WaitGroup

    ch1 :=make(chan int)

    wg.Add(2)
    go printNumbers(&wg,ch1)
    go generateNumbers(3, &wg)

    fmt.Println("Waiting for goroutines to finish...")
    wg.Wait()
    fmt.Println("Done!")
}

I'm trying to pass data (value of Sum ) from generateNumbers to printNumbers routine.

But I encountered the following problem:

Waiting for goroutines to finish...
Generating number 1
Sum is now%!(EXTRA chan int=0xc000102060)Printing number 1
Printing number 2
Printing number 3
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [semacquire]:
sync.runtime_Semacquire(0xc000118270?)
    /usr/local/go/src/runtime/sema.go:62 +0x27
sync.(*WaitGroup).Wait(0x4ba3a8?)
    /usr/local/go/src/sync/waitgroup.go:116 +0x4b
main.main()
    /tmp/tgPhZuPV77.go:42 +0x12f

goroutine 19 [chan send]:
main.generateNumbers(0x3, 0x0?)
    /tmp/tgPhZuPV77.go:19 +0xf2
created by main.main
    /tmp/tgPhZuPV77.go:39 +0xe5
exit status 2

Please help, I am new to Golang.

Solution

There are some errors in the above program.

1. The two functions printNumbers and generateNumbers must use the same chan variable.
2. You should read the data of chan variable from ch.
3. The function generateNumbers should not declare and create chan variables repeatedly.

I modified the above code as follows:

func generateNumbers(total int, wg *sync.WaitGroup, ch chan int) {
    defer wg.Done()

    sum := 0
    for idx := 1; idx <= total; idx++ {
        fmt.Printf("Generating number %d\n", idx)
        sum = sum + idx
        ch <- sum
    }
}

func printNumbers(wg *sync.WaitGroup, ch chan int) {
    defer wg.Done()

    fmt.Printf("Sum is now:\n")
    for idx := 1; idx <= 3; idx++ {
        sum := <-ch
        fmt.Printf("Printing number %d %d\n", idx, sum)
    }
}

func main() {
    var wg sync.WaitGroup

    ch1 := make(chan int)

    wg.Add(2)
    go printNumbers(&wg, ch1)
    go generateNumbers(3, &wg, ch1)

    fmt.Println("Waiting for goroutines to finish...")
    wg.Wait()
    fmt.Println("Done!")
}

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