Golang：在多个goroutine中发送关闭通道错误

Question

I have 3 channels that get data from together . My code run for first time perfect but when after that I send another data , there is error : send on closed channel.In func FillNotCheckedDeliveryCh that line I closed channel .If I do not close it app stopped and not continue.

func main() {
    receiveBulkIdsCh := make(chan int64, 100)
    NotCheckedDeliveryCh := make(chan CommonType.BasicRequestParameters, 100)
    ResultCh := make(chan CommonType.MessageStateResult, 100)

    var wg sync.WaitGroup
    wg.Add(4)

    /* Every BulkIds that receive from queue , save in  receiveBulkIdsChan channel*/
    go func() {
        defer wg.Done()
        PopQueue(receiveBulkIdsCh)
    }()
    go func() {
        defer wg.Done()
        for BulkId := range receiveBulkIdsCh {
            FillNotCheckedDeliveryCh(data, NotCheckedDeliveryCh)
        }
    }()
    go func() {
        defer wg.Done()
        for item := range NotCheckedDeliveryCh {
            for msgStatus := range DoFuncGetMessageState(item) {
                ResultCh <- msgStatus
            }
            close(ResultCh)
        }
    }()
    go func() {
        defer wg.Done()
        for Result := range ResultCh {
            ReadResultCh(Result)
        }
    }()
    wg.Wait()
}

func FillNotCheckedDeliveryCh(data IntegrateRowsFields, ch chan<- CommonType.BasicRequestParameters) {
    ch <- PackerForNotFinishedCh(data)
    defer close(ch)
}

can help what's wrong ?

Answer 1

When you work with channels in Go always the sender should close the channel. Because that signals that no more data will be send over the channel.

In your code the receiver is closing it. Just leave the channel here opened and remove the close(ch) there.

func FillNotCheckedDeliveryCh(data IntegrateRowsFields, ch chan<- CommonType.BasicRequestParameters) {
    ch <- PackerForNotFinishedCh(data)
    defer close(ch)
}

If something is blocking at that part you could use select:

func FillNotCheckedDeliveryCh(data IntegrateRowsFields, ch chan<- CommonType.BasicRequestParameters) {  
    select {
      case ch <- PackerForNotFinishedCh(data):
      default:
    }
}