I’m having trouble trying to work out how to update a slice from parallel goroutines. I initially came up with this code (that I knew wasn’t the correct way to do it!):

func main() {

    var dwpList = []int {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    var mmrpList []int
    
    var wg sync.WaitGroup

    ch1 := make(chan int)

    cores := 4

    wg.Add(cores + 1)

    for i := 0; i < cores; i++ {
        go func1(&mmrpList, ch1, &wg)
    }

    iterateSamples(dwpList, ch1, &wg)

    close(ch1)

    wg.Wait()

    fmt.Println(mmrpList)

}

func iterateSamples(dwpList []int, ch1 chan<- int, wg *sync.WaitGroup) {

    defer wg.Done()

    for _, dwp := range dwpList {
    
        ch1 <- dwp
    }
}

func func1(mmrpList *[]int, ch1 <-chan int, wg *sync.WaitGroup) {

    defer wg.Done()

    for dwp := range ch1 {
    
        *mmrpList = append(*mmrpList, dwp)
    }
}

Obviously this doesn’t work as there are multiple goroutines appending to the slice at the same time.

The problem is, whenever I try to move the append into it’s own function controlled by extra channels, waitgroups, etc. I always run into compile or ‘deadlock’ issues (which aren’t always deadlocks but a wg Wait or Done issue), or it reverts back to being single-threaded.

Can you please guide me as to how this should be achieved?