Golang中的静态全局变量

Question

I am new in Go language and I need some help. I have declared a global variable but the problem is that it does not keep its value. It would be solved with a static variable but no such variables exist in Go. How should I solve this?

gID is a global variable. This function is called twice. On the first call if code is executed. On the second, else code is executed. I want the second struct Learner instance, to get first Learner's instance ID.

I have to mention that NewLearner is called twice from two different files from different packages.

func NewLearner(name string, peerURLs types.URLs, clusterName string, now *time.Time) *Learner {

    l := &Learner{
        RaftAttributes: RaftAttributes{PeerURLs: peerURLs.StringSlice()},
        Attributes:     Attributes{Name: name},
    }

    var b []byte
    sort.Strings(l.PeerURLs)
    for _, p := range l.PeerURLs {
        b = append(b, []byte(p)...)
    }

    b = append(b, []byte(clusterName)...)
    if now != nil {
        b = append(b, []byte(fmt.Sprintf("%d", now.Unix()))...)
        hash := sha1.Sum(b)
        l.ID = types.ID(binary.BigEndian.Uint64(hash[:8]))
        gID=l.ID
        return l
    }  else {
        l.ID = gID
        return l    
    }

}

Answer 1

The fact that the package variable doesn't keep its value might be caused by concurrency. I would solve your problem that way. Use a package variable with a mutex around in case the function is called concurrently.

import "sync"

var(
    gID  uint64
    muID sync.Mutex
)

func myfunc(param bool) {
    var id uint64
    if param {
        id = newID()

        muID.Lock()
        gID = id
        muID.Unlock()
    } else {
        muID.Lock()
        id = gID
        muID.Unlock()
    }
}