在go例程中更新后不返回更新后的值

Question

I am running into a problem where integer value being returned is same as the one set, even after the value is updated in a go subroutine. I cannot seem to figure out whats wrong.

//HostUptimeReporter - struct
type HostUptimeReporter struct {
    updateInterval int
    uptime int
    shutdownSignal chan bool

}

//NewHostUpTimeReporter - create reporter instance
func NewHostUpTimeReporter(updateIntervalInSeconds int) HostUptimeReporter {
    instance := HostUptimeReporter{updateInterval: updateIntervalInSeconds, shutdownSignal: make(chan bool), uptime:59}
    ticker := time.NewTicker(time.Duration(updateIntervalInSeconds) * time.Second)
    go func() {
        for {
            select {
            case <-ticker.C:
                instance.uptime += updateIntervalInSeconds          
                fmt.Printf("updated uptime:%v
", instance.uptime)
            case <-instance.shutdownSignal:
                ticker.Stop()
                return
            }
        }
    }()

    return instance
}

//Shutdown - shuts down the go routine
func (hupr *HostUptimeReporter) Shutdown(){
    hupr.shutdownSignal <- true
}

func main() {

    hurp := NewHostUpTimeReporter(2)
    defer hurp.Shutdown()
    fmt.Printf("current uptime:%v
", hurp.uptime)
    time.Sleep(3*time.Second)
    fmt.Printf("new uptime:%v
", hurp.uptime)

}

https://play.golang.org/p/ODjSBb0YugK

Any pointers are appreciated.

Thanks!

Answer 1

The function that launches the goroutine returns a HostUptimeReporter:

func NewHostUpTimeReporter(updateIntervalInSeconds int) HostUptimeReporter {

Returning a whole struct like that returns a copy of the struct so the goroutine and the NewHostUpTimeReporter caller are looking at different things. You want to return a pointer so they're sharing data:

// -----------------------------------------------------v
func NewHostUpTimeReporter(updateIntervalInSeconds int) *HostUptimeReporter {
    instance := &HostUptimeReporter{updateInterval: updateIntervalInSeconds, shutdownSignal: make(chan bool), uptime:59}
    // ---------^
    ...